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Circuit Board Repair
by firstname.lastname@example.org, 11/02/13.
Copyright 1999-2014, all rights reserved.
Don't Over Estimate your Repair Abilities!
Table of Contents
1a. Before Beginning: Introduction to Pinball Repair
But a very simple thing that is often asked is, "what equipment is needed to fix a pinball?" This document covers the electronic equipment needed, and how to use it. And the other repair guides cover the basic non-electronic tools needed for each system of games. But for completeness (since we mention all the electronic equipment needed below), here are some basic non-electronic tools need for pinball repair.
Beyond the basic tools, a level of "common sense" is also needed when fixing games. Remember the people that designed these games were probably much smarter than you and I, so we need to trust their design (unless I tell you otherwise, ha!) If they have a connector on a board, and it is burnt, it's best to replace it (and not solder wires directly to the board, circumventing the connector, and making the game "unservicable" in the future!)
As my buddy Kirb says, "Now let's start with some basics. Do you know what an amp or volt is? Do you know that electricity can kill you? Are you scared to look under the playfield of your game when it is turned on? Think about all of this before trying to save $100 and fixing a game yourself. For those of us dumb enough (like me) to waste time working games, we should all first learn how to do so." Hopefully this document (and some common sense) should save a new pinball learner some trouble.
1b. Before Beginning: Should you attempt Printed Circuit Board (PCB) repair?
If the answer is "no" to ANY of these questions, STOP! Do not work on circuit boards! Send them out for repair to a professional. In the end, much more money will be saved having the boards fixed professionally, then attempting to repair them yourself.
Keep in mind some pinball circuit boards are not replaceable! So if a board is made "non-serviceable" (unusable), a lot more money can be lost than a professional repair would have cost in the first place. In some cases, it is possible to make a game "junk" if a non-replaceable circuit board is ruined.
This is the key point to this document. Do not think because all the procedures here look easy and anyone can do them! Do NOT become over confident. A "hack" repair can RUIN a circuit board. And most repair facilities will not fix circuit boards that have been unsuccessfully repaired ("hacked") by someone else.
1b. Before Beginning: How did you learn to solder?
I remember when I first learned to solder. My dad taught me with a soldering pencil, some paper clips, and some rosin core solder. I was probably 10 years old, and I thought it was fun! What he had me do first was make a box out of the paper clips. Using needlenose pliers, I constructed one side of the three dimensional box. Then I soldered the points where the paper clips came together. When I was done, it was a pretty nifty 3-D box, and I was proud.
Nostalgia aside, this was a good first experience. It taught me how to solder, at the expense of only some paper clips. If one has novice soldering skills, start small and practice! Sacrifice some paper clips and make a "box".
1b. Before Beginning: Practice makes Perfect.
Basic soldering is pretty straight forward. Get a soldering station and some good quality solder (as decribed below). Having the right tools is 75% of the job! And remember, a good solder job on a coil or switch starts with a good *mechanical* connection. That is, the wire should be mounted to the coil or switch lug before being soldered, and stay put! After that, soldering the wire is just a matter of heating the wire and the lug *together*, and then applying a small amount of solder. The solder should be applied to the wire or lug, and *not* directly to the soldering iron's tip. This ensures the solder will flow over the wire and the lug, and that they are heated to the right temperature. The soldering iron can then be removed from the joint. Now keep the solder joint steady while it cools, otherwise it could produced a "cold" solder joint (one that does not conduct electricity freely).
Once this basic soldering is mastered, the next step (maybe!) is solder on a Printed Circuit Board (PCB). If one has never soldered a PCB before, don't try your first attempt on a (expensive!) pinball CPU or Driver board! Practice on some junk boards first.
Junk circuit boards are easy to get. Video game collectors can often provide some junk JAMMA games board or other boards. Maybe there's an old PC computer (which you couldn't give away!) that's could be used. Practice circuit boards aren't that hard to find. You just gotta look. Even if one has to pay for some junk boards, it's well worth it.
Another alternative is to go to Radio Shack and buy some cheap resistors (about 50 cents for five), and some "breadboard" print circuit board material with holes, part number 276-150 at $1.19, or part number 276-168 at $2.49. Practice soldering the resistors to the board. This is not as good practice as using a real printed circuit board though (there's nothing like the real thing). Remember to clean the copper on the Radio Shack board with some Scotchbrite before trying to solder them (unsoldered virgin copper likes to oxidize, making soldering difficult). But please read the tips and info below before starting.
2a. Tools Needed: Good Lighting and Magnification.
A good magnifier allows examination of circuit boards in great detail, to view repair work quality. There are two types of magnifiers available. One is worn on the head, and it requires an external light source. To focus, move your head to a certain distance from the viewing object. The other (more desirable in my opinion) magnifier is on an adjustable "arm", and has a built in light source. This is what I personally prefer, and I find it extremely useful for finding circuit board defects. MCM Electronics (800-543-4330) sells these, part number 21-935 for $49, but it's often on sale for $39. This is a nice version with a built in circular florescent lamp. There is also a cheaper version with a standard incandescent light bulb for about $29 (often on sale for $19), part number 22-3995, but the florescent lamped model is much nicer.
If one is absolutely cheap and broke, a Magna-Lite lighted magnifier reader is also available. This hand-held device works well too, and can fit in a pocket. It has a high intensity bulb with a switch. Available in 4x, part number 21-6595, for $6.99, from MCM Electronics.
2b. Tools Needed: Get a good Soldering Station.
Buy a Good Soldering Station.
I personally like the Weller brand (USA made) soldering stations. Weller even makes a nice "budget" brand under the Weller Ungar name. If you are really on a budget, the Tenma brand (import) is decent too. I personally use a Weller station for my workbench, and use a Tenma for the garage. Which ever you get, buy some extra soldering tips! I prefer the "chisel" soldering tip shape (1/16" wide), opposed to the "cone" shape.
The important thing to get in a soldering station is temperature control, and not some goofy variable rate that has no reference point (like "1 to 10"). An actual temperature range is important. Soldering is best done at 600 to 700 degrees (personally I usually solder at about 650 or 700 degrees), but a decent soldering station is usually adjustable from 300 to 900 degrees. A soldering station that doesn't provide a temperature guage is probably varying the wattage, and not the temperature. This is far less useful.
For cheap soldering irons, the wattage of the iron is a measure of the power that is used to heat the iron. So a 25 watt soldering iron is always running at that level of power consumption (like a 25 watt light bulb would), and is ALWAYS generating heat. The soldering iron's tip absorbs the heat. As long as power is supplied the tip will continue to get hotter until it reaches "equilibrium" (the maximum temperature where heat will be conducted to the air at the same rate heat is applied to the tip). As soon as a soldering iron's tip makes contact with metal, heat will transfer from the tip quickly. The higher the wattage iron, the quicker the tip will heat up again. When a cheap soldering iron is idle, it is MUCH HOTTER than it needs to be for soldering. But the moment you place it on metal for soldering, it cools down. For this reason, if not using a cheap soldering iron for more than 5 minutes, turn it off. Otherwise it will get too hot and ruin the iron's tip (at minimum), or apply too much heat to the solder joint (at worse).
The above is why cheap soldering irons are bad; there is no way to control the actual temperature of the iron! That's why a good soldering station is really a must. The right temperature can be dialed in. Then the station will monitor itself, turning power to the station's soldering tip on and off as needed to maintain the desired temperature. Good soldering stations also provide a level of isolation so static sensitive chips won't be easily ruined by the soldering iron.
Tenma's soldering station with LED temperature display #21-7930 (formerly #21-147) is available from MCM Electronics (800-543-4330) for $75 ($40 on sale). Tenma also has a digital display version of this station for $100 (often on sale for $60) #21-7935. Also get some replacement soldering tips, screwdriver "chisel" style #21-7983 (formerly #21-927, 3/64" wide chisel tip for circuit board work) and #21-926 (1/6" wide chisel tip for bigger jobs like coils) for $2.49 each. Then even sell a complete replacement grounded iron (with tip) for these two station #21-7936 (formerly #21-151) for $10.
Finally Weller's WES50 soldering station is also available from MCM for about $110 (often on sale for $100). This model has adjustable temperature range from 350 to 850 degrees (though the scaling is strange). The Weller brand will cost a bit more, but is probably worth the extra money.
I'm Poor; Must I Spend $70 on a Soldering Station?
2c. Tools Needed: Get good solder!
Rosin core flux is very important. Any other type of flux will not work for circuit board repair. For example, acid flux is designed for plumbing work, not electronics! Most hardware stores only sell 95/5 lead free solder, which won't work for circuit board repair. Radio Shack's solder is made by Kester, and is quite good.
Solder diameter is also important. Anything bigger than .032" is usually too big, and will put too much solder on the circuit board. I use .032" for everything, including coils and fine circuit board work. Some people like to have the larger .040" or .062" solder around for soldering wires to coils, and other larger soldering jobs. But personally I don't see the need for it.
2d. Tools Needed: DeSoldering Tools.
Replacement tips come in a variety of hole sizes. The "standard" hole diameter is about .040". This size will work for most pinball desoldering applications. Personally I tend to go .050" or even .060", as desoldering .156" Molex male header pins are usually too big for a .040" tip.
The downside to solder braid is heat. Usually it takes more heat to unsolder using braid. Also it's not very fast. If doing a lot of unsoldering, it will take some time and lots of patience. It works OK with large holes to desolder. But when desoldering say a chip with small leg holes in the circuit board, I find the braid difficult to use. I personally don't recommend it or use it, but it does work in a pinch, and it's inexpensive.
For the average hobbyist, this is an usable desoldering tool. The Radio Shack desoldering iron is part number 64-2060, $9.99. It is simply a 45 watt soldering iron with a hollow tip, and a red suction bulb. After letting this iron warm up for about 15 minutes, compress and hold the red bulb. Then put the hollow tip over the joint to desolder. After the solder has melted (a couple seconds), release the red bulb, and the solder will be sucked from the joint (this theory is how expensive desoldering stations work). An easy one handed operation that requires minimal practice.
But this style of desoldering tool comes with the same warning as non-adjustable temperature soldering irons; the amount of heat applied can *not* be adjusted! Because of this, the Radio Shack desoldering iron can be dangerous. Too much heat, and the traces and solder pads can delaminate from the circuit board! Just keep this in mind. Remember, it is a 45 watt desoldering iron, so it generates *lots* of heat. With a little practice, the Radio Shack desoldering iron can work well. It's hard to beat for the price, and I personally find it easier to use than most other low-cost desoldering tools. But too much heat can be applied with this tool, making it dangerous for the "newbie". Because of this, I would not recommend this tool for first time users unless they practice a lot on junk board first.
Also make sure to buy extra tips for this desoldering tool. They sell two styles of tips; get the "iron clad" version, which costs about 70 cents more, part number 64-2062, $1.99 (the iron clad version will last much longer than the standard version). A clogged or enlarged tip on this tool will render it useless.
Desoldering Vacuum Pumps (Soldapullt); Newbie Recommended!
The biggest advantage to a Soldapullt tool is a soldering station can be used to heat the joint being desoldering. This means the desoldering temperature can be controlled via the soldering station. This is probably the single biggest advantage to using the Soldapullt desoldering tool (aside from price). Because of this, I highly recommend the Soldapullt tool for first time "newbie" repair people. But remember, practice is necessary to use it! So find some junk boards and try it out (instructions on how to use this tool are below).
Better (more expensive!) Desoldering Irons.
I can't stress how much better these units are than the previously discussed and less expensive desoldering tools. If working on any games that require a fair amount of desoldering, these tools will make the job FAR easier, faster, and less problematic.
Other Desolder Parts to Buy.
Also all desoldering stations also use some sort of filter to keep the old solder from getting into the air source (this filter is usually located in the solder collection tube). The filter could be as simple as a (100%) cotton ball (do NOT use synthetic cotton, as it will melt!) Have some spare filters around, and be prepared to replace this filter every now and then. Another replacement item is the rubber gasket that seals the solder collection tube to the "Y" adaptor. With time these dry out and fall apart. So it's not a bad idea to have a few of these rubber gaskets around too.
Finally, many desoldering stations also offer a declogging "toolkit" that includes a set of miniature round files. These are used to clear the desoldering tip and adjacent "Y" adaptor of any stuck solder. It's a good idea to have one of these toolkits too, if it didn't come with the new desoldering station.
Buying a Used Desoldering Station (Ebay).
What Ever You Use, PRACTICE!
2e. Tools Needed: DMM (Digital Multi Meter).
An electronic pinball game repair should not even be attempted without a decent DMM. It's probably the single most valuable tool. The best name in DMM's is probably Fluke. But for pinball repair purposes, any decent brand will probably work fine.
Optional, but nice to have:
Auto ranging meters are great for beginners. Manual ranging meters require the user to know something about the part they are testing. For example, if testing a 1 meg ohm resistor, but the meter is set to the 10k ohm range, the resistor will show as "open" (null resistance). The meter needs to be set to a higher resistance range for this test. This means the resistor or schematic needs to be examined before testing it, to figure out what its value *should* be (based on the schematics or the resistor's band colors), Then the DMM is set accordingly.
In the case of an auto ranging meter, it does an initial test on the resistor, and figures out the correct range. All the user needs to do is to set the meter to "resistance", and it figures out the rest.
What are the Disadvantages to Auto Ranging DMM's?
DMM Leads and Clips.
Cheap DMM's are No Bargain.
2f. Tools Needed: Logic Probe.
To understand why these "pulses" are important, some basic computer hardware concepts need to be understood. Simply put, a electronic pinball game is a computer. Computers (at a low level) can only deal with zeros and ones. A "zero" is basically zero volts DC (.8 volts or less). A "one" is basically +5 volts DC (2.4 volts or greater). The relationship between these two signals (voltages) is important. How fast or often a circuit goes from zero to +5 volts can determine how a circuit works. A logic probe can show if a particular pin on a chip is low (zero volts), high (+5 volts), or pulsing. The pulses can be "low pulses" or "high pulses" too. The logic probe shows this with three LED's, and sometimes a buzz tone too.
Unfortunately, a logic probe only indicates state changes (a zero or a one, which is 0 volts to .8 volts, or 2.4 volts to +5 volts, respectively). It is up to you to know if these are the expected changes!
Are All Logic Probes the Same?
Radio Shack used to sell a decent logic probe at for $17.99, part number 22-303, but apparently Radio Shack is discontinuing these. MCM Electronics (http://www.mcminone.com) also sells a nice Tenma logic probe with memory, part number 72-190, for less than $25.
By far my favorite logic probe is made by Wittig Technologies (wittig-technologies.com). It's called the osziFOX Probescope, and it's a "probe style oscilloscope". It is a 5mHz (DC band width, other specifications available here) logic probe with a small LCD display screen, which draws a picture of the signal. It can even be interfaced it a computer through the serial port (giving a larger, more oscilloscope usage), or to a Palm Pilot IIIc! It runs on 9 to 13 volts DC (much like a regular logic probe). A pretty neat device, available from Test Equipment Depot (1-800-517-8431) for $ 69.00, or directly from the manufacturer at wittig-technologies.com. It gives a nice picture of what the signal pulses look like. Though I still recommend having a "regular" logic probe, this device is really cool and more like an oscilloscope. For someone just starting out in repair, this device really helps "see" what signals should look like. I personally find the "picture" which this probe draws as very useful (though it is no substitute for a real oscilloscope, which shows a picture of the signal in a time relationship).
2g. Tools Needed: Hand Crimpers.
3a. How to Use It: Electronic Schematic Symbols.
3b. How to Use It: Short Course in Transistors.
What is a transistor? Transistors are tiny components which amplify small signals using low voltages. Transistors are basic components in all of today's electronics. They are just simple switches that we can use to turn things on and off. Even though they are simple, they are the most important electrical component. For example, transistors are almost the only components used to build a Pentium processor. A single Pentium chip has about 3.5 million transistors.
The transistor has three legs, the Collector (C), Base (B), and Emitter (E). The Base (B) is the on/off switch for the transistor. If a current is flowing to the Base, there will be a path from the Collector (C) to the Emitter (E) where current can flow (the switch is on). If there is no current flowing to the Base, then no current can flow from the Collector to the Emitter (the switch is off).
When current is put into the Base, it changes the voltage characteristics of the entire transistor, and so it is possible to control the current flowing from the Collector to the Emitter. So a small change of current on the base, results in a large change between the Collector and Emitter.
PNP = Pointing iN Pointer. The PNP transistor's arrow points in.
NPN and PNP transistors function in essentially the same way, just the power polarities are reversed. This means a NPN transistor has a higher frequency response than a PNP transistor (because electron flow is faster than hole flow). When a NPN transistor is doing-its-thing, there is always a constant 0.6 volt drop between the base and emitter. That is, the base is always about .4 to .6 volts more positive than the emitter. We will see this come into play when we test transistors using a DMM (digital multimeter).
Bipolar transistors are often used in pinball, and are a current driven device. This means a very small amount of current flow from the emitter to base can control a relatitively large current flow from the emitter to the collector.
Darlington transistors (for example, the TIP102 and TIP36c) are actually two transistors in one package. This is achieved by arranging the two transistors so the emitter of one is driving the base of the next, and by connecting the collectors together. This is known as a Darlington pair, and can be used as any single transistor would be used (common emitter, emitter follower, etc.) The advantage to this style of transistors is it has a larger on-state power dissipation (which means these Darlingtons can handle lots of current for driving big pinball coils such as up-kickers and flippers). The down side to Darlington transistors is reduced power-on/power-off speed.
3c. How to Use It: Short Course in Logic Chips.
Every chip has a "pin 1". Find pin one, because this is the reference point for all the other chip pins. Also pin one is the reference point to how the chip should be inserted into the board or socket. Putting a chip in "backwards" will definitely cause the chip to fail!
Pin one on all chips is marked somehow. Often there is a small dot impressed into the case of the chip signifying pin one. Other times there is a notch in the chip showing pin one. In this case pin one is always to the left of the notch (as facing the chip's top side, with the notch up). Sometimes chips have both a notch and an impressed dot!
Pin one is also marked on all sockets too. Again, sockets generally use the "notch" in a cross bar for indicating pin one. This notch helps when replacing a chip, so it is not plugged in backwards! Some sockets use an indented cross bar to indicate pin one, instead of a notch.
Often the circuit board itself is also silk screened to show pin one for each chip. Again, this could be a box that shadows the chip, with a notch in one side of the box to show pin one. Or it could be as simple as a "1" or a "dot" next to the chip's pin one leg.
How are the Pins Numbered? (or where is the last pin?).
Any electronics dealer that sells NTE or ECG parts will have one of these guides available. Often older copy of this guide can be had for free, or just a couple dollars. The latest version is not needed, as most chips being referencing have been out for a number of years.
Online Chip Reference Guides.
Explaination of TTL Chips.
The TTL family has at least six sub-families which offer different speed/power tradeoffs. These are summarized in the following table, where they are listed in roughly the order in which they were introduced:
The term Schottky refers to a technology for making faster transistors. In each generation of the TTL family, the low power representative is about 3 times slower than the other member, but consumes about 1/10 the power. Today, the low-power Schottky (LS) subfamily is the most widely used member of the TTL family.
TTL chips have a standard naming convention of 74xx or 54xx. All manufacturers of TTL chips use this common naming system, as exemplified by the chip name SN74LS00. The prefix SN indicates that the chip was made by Texas Instruments; other manufacturers have their own prefix codes. However if the remainder of the chip name matches, the chips should perform exactly the same function. Additional one letter codes may be added as prefixes or suffixes to this code, for example, RSN indicates radiation hardened chips made by Texas Instruments, and SNM indicates the use of quality control procedures specified by the military specification MIL-STD-883.
The numeric code 74xx indicates that the chip conforms to the requirements of the civilian computer industry, being able to operate over a temperature range of 0 to 70 degrees C, while the code 54xx indicates the ability to operate over the more extreme temperature range of -55 to 125 degrees C required by many military and industrial applications. The letters LS (in the example SN74LS00) indicate which subfamily the chip belongs to. Finally, the last two digits indicate the logical function performed by the chip.
Here is a list of a few common TTL chips:
The descriptions of these circuits are based on the details given in The TTL Data Book published by Texas Instruments. Equivalent data books are published by all of the major chip manufacturers such as Signetics, National Semiconductor, ECG and NTE.
Each circuit description in the TTL collection follows a common scheme.
The input and output pins of the chip have numeric names corresponding
to the pin numbers used for a dual-in-line package; for example,
for a 14 pin chip, these are
HCT and HC Chips.
However don't sustitute HC for LS or any other TTL family without looking at the specifications, as HC chips are not compatible with TTL chips. They are high speed CMOS but with no TTL interface (HC chip expect much higher input levels for a logic "1" and a much lower input level for a logic "0"). The HC parts have similar interface levels to the old 4000 series IC's, except the HC parts usually run much faster.
For example, compare a CMOS 4069 Hex Inverter, which is a functional equivalent of the 7404 TTL (not "pin compatible", which mean you can't just plug a 4069 in place of a 7404). In this case, we know if a given input has a state of high (1) on the 7404 TTL, then it's output would be inverted to be low (0). After all, this is what a "Hex Inverter" does! But the CMOS 4069 would be different; first it's input state could be a voltage range from 0 to the operating voltage, say in this example, +12 volts. So if the input voltage for a given gate was +4 volts, then the output would be +8 volts, which is the inverse proportion of the input relative to the operating voltage (12 volts).
CMOS is useful for handling audio and video outputs, or any situation where the input voltage is not just a "black and white" zero or one.
3d. Component Explainations and How to Test Components Using a DMM (voltage, continuity, resistance, capacitance, diodes, transistors, chips).
Again, if the DMM has manual ranges, the range must be set above the voltage being testing. When measuring DC volts, the black DMM lead goes on ground, and the red lead on the voltage you are measuring. If measuring AC (alternating) voltages, this doesn't matter (since AC voltage changes from positive volts, to zero volts, to negative volts, back to zero volts, many times per second).
For example, if I had to remove a chip from a circuit board and install a socket, I always test each pin of the socket to make sure it connects to the circuit board trace it is soldered. This ensures I haven't broken or cracked a trace while removing the old chip.
With my DMM set to "continuity", I can "buzz out" two points with the DMM's test leads. With one lead of the DMM on a socket pin, and the other DMM lead on the trace that connects to the socket, there should be a "tone" (or "buzz") indicating continuity. No buzz means these two points aren't connected (or are connected with high resistance).
If your meter does not have a continuity setting, just use the lowest range of resistance ohms for this test. Zero ohms (or close to zero, like less than 1 ohm) means you have continuity. The disadvantage to not having a continuity setting is you must LOOK at your meter to see if you have continuity. With a continuity setting, one only needs to HEAR the buzz tone, instead of seeing the meter. This makes checking continuity on a number of test points much faster.
Resistance testing is much like testing for continuity, but usually the value of a resistor is being tested. If a manual range DMM is used, one will need to know the basic value of the resistor being tested (so the DMM's ohm range can be set accordingly). If the DMM is set to the 10k range, and the resistor being tested is 12k ohms, the meter will show no value.
Most resistors can be tested "in circuit". That is, with them soldered right in the circuit board (without removing them). Just put the leads of the DMM on either end of the resistor.
Are Resistors Polarized?
Here is a resistor color code chart for the first three color bands of any resistor. The third band is the "multiplier" band:
The last (fourth) band is the tolerance band (how accurate the resistor is to its stated value), plus or minus. Here are those colors:
With the above info, a manual range DMM can be accurately set. Remember, always pick a DMM range higher than the resistor value being tested, but never lower. If a resistor is more than 10% above or below it's intended value, replace it (even though some resistors are rated at as much as 20% out of tolerance).
On-line Resistor Color Chart.
Put the black lead of the DMM on the banded side of the diode, and the red lead on the non-banded side. A reading between .4 and .8 volts should be seen. If a reading outside this range is noted, remove one lead of the diode from the circuit and test again. If still getting a reading outside of this range, then the diode is probably bad.
Switch the leads of the DMM (red lead on the banded side of the diode), and a null or zero reading should be seen on the DMM. If getting a different reading, remove one end of the diode from the circuit board and test again. If a null reading is not seen, the diode is bad.
Are Diodes Polarized?
Remember a higher amp and/or higher voltage diode can usually be substituted. For example, a 1N4001 diode is rated at 1 amp 50 volts. A 1N4004 diode, rated at 1 amp 400 volts, can be used in its place (the most commonly used diode in pinball is the 1N4004). Bridge Rectifiers (essentially four diodes in one package) are the same way (an increase in peak voltage and/or amps is OK). In pinball 1n4001 diodes are often used on 12 volt switch matrix switches, and 1n4004 diodes are used on 30 to 70 volt coils. But in either application, a 1n4004 diode will work fine.
Zener diodes can not be substituted as easily. These diodes are rated at a particular voltage and wattage. This voltage in nearly all circuits must be the same. Only the amp rating can be increased. For example, a 1N5237 zener diode is an 8.2 volt 1/2 amp Zener diode. A 1N4738 can work too, as it is 8.2 volts but at the a higher 1 watt power rating). And a 1N4196 (8.2 volt 10 amps) could be substituted because it still maintains the 8.2 volts, but at 10 amps. In most pinball applications 1/2 or 1 watt zener diodes are common (I personally always replace a 1/2 wat 1N52xx zener diode with a 1 watt 1N47xx version).
Testing Bridge Rectifiers.
A bridge has four terminals: two AC terminals, and two DC terminals (postive and negative). On the side of each bridge, printed on the metal casing, there should be two labels: "AC" and "+" (also the "+" lead should be offset in position compared to the other three bridge leads). Figuring out the other two terminals is easy: the other AC terminal is diagonal to the labeled AC lead. The negative DC lead is diagonal to the labeled (and offset) positive DC lead. Testing a bridge while soldered in the board (in curcuit) may not give the following results. To test the bridge:
If values outside of .4 to .6 volts are shown for any of the above tests, the bridge is bad. Typically seen is a zero value (a short) or a null reading (a bridge diode is open) in at least one of the above tests.
Transistors and Chips.
For the most part, the most common testing will be on "darlington" transistors (which means they are actually two transistors in one package) such as the TIP102, TIP122, TIP36 transistors. Also most testing is done "in circuit" (installed in the circuit board). For each of these have one lead of the DMM on the metal case (tab) of the transistor (which is usually the center leg of the transistor). Then the other lead of the DMM will test the outside two legs individually. A value of .4 to .6, or 1.0 to 1.2 should be seen, depending on the exact transistor, and which lead (red of black) is on the metal tab. The biggest indicator of a bad transistor would be a value less than .2 (probably a short). Look to the specific pinball repair guides for more exacting details of this. Also remember, a transistor can ocassionally test as "good", but in fact be bad.
To test chips, the ground leg of the chip in question will need to be known (that's why we went through the "short course on logic chips" above). Then put the RED lead of the DMM on this ground leg. Yes I know, it sounds weird. "Why the RED lead on the ground leg? Isn't that backwards?" Backwards or not, that's how to do it. With the red lead on the ground pin, check all the other pins (except for VCC, which is the chip power pin) with the black lead of the DMM. Again .4 to .6 volts should be seen for each leg. If a different value is seen, chances are the chip is bad. The biggest indicator of a bad chip would be a value less than .2 (probably a short).
Capacitor Values and Terminology.
For a comparison, .039 microfarad (uF) is the same as .000039 millifarads (mF).
Another confusing thing about caps are how they are sometimes labels. For example, often ceramic capacitors will say "104" on them. Most caps will have three numbers, but sometimes there are just two numbers. These are read as Pico-Farads. An example, "47" printed on a small ceramic cap can be assumed to be 47 picofarad. If there are three numbers, it is somewhat similar to a resistor code. The first two numbers are the first and second significant digits, and the third is a multiplier code. Most of the time the last digit tells you how many zeros to write after the first two digits (in picofarads), but the standard has a couple of curves. To be complete here it is in a table:
Example: A cap marked "104" is 10 with 4 more zeros or 100,000 pF, which is otherwise referred to as a .1 microfarad cap. A cap marked "103" is 10 x 103 pF or .01 microfarad. Likewise "102" is 10 x 102 pF or .001 microfarad. Here's a table for ease:
In addition there can be a letter after the cap code. This tells the tolerance of the capacitor:
For example, a cap marked "33J" would be a 33 picofarad cap with +/- 5% tolerance.
Electrolytic Caps - Radial or Axial?
Testing Capacitance - Testing Capacitors.
Of course the best way to test a capacitor is to just replace it with a new one! This isn't always cost or time effective, but it is really the best course of action if a capacitor is suspected as bad.
The Best Capacitor Tester - the ESR Meter.
The best deal on an ESR meter is the Dick Smith ERS, available at anatekcorp.com/testequipment/esr.htm. It's about $130 fully assembled. This is generally considered the best ESR meter, especially for the price. Also available is the Capacitor Wizard at about $200. Another assembled meter is the CapAnalyzer 88A, sold by MCM Electronics (800-543-4330), part number 72-6508, $179.
Are Capacitors Polarized?
If testing an electrolytic capacitor (which has "polarity"; marked positive and negative leads), make sure to put the red lead of your DMM on the positive lead of the cap when testing.
Similar Capacitor Values.
Some Williams solidstate games use an inductor or choke, which is mearly wire wrapped around a ferrite core. An inductor filters or chokes out certain signals (frequencies). Inductors are measured in microhenries, and are most often denoted as "L", which is the inductance in microhenries (mH). Nanohenries is denoted as nH. For example, a 10 microhenries (mH) inductor is used on the B.S. Dracula long-range opto board.
Other Component Testing Info.
3e. How to Use It: Logic Probe.
Finding Power Points for the Logic Probe.
Probes have two power clips: black for ground, and red for power (+5 to 12 volts). With the game turned off, connect these leads to known good voltage points. Then power the game on. On pinball games, I like to find power "test points" on the driver board. I use the +5 volt test point for the red lead of the logic probe, and attach the black lead to a ground test point (or even the metal ground strap in the head).
First make sure the "TTL/CMOS" switch on the logic probe is set to "TTL". Then after the logic probe has power, the metal "point" on the logic probe is now touched to pin on a chip in question. BE CAREFUL! Don't touch two chip pins at once, shorting them together! If this does happen, I personally turn the game off and start over (and hope nothing is damaged, which is usually the case).
The logic probe will tell if the pin chosen is either "high" (at +5 volts), "low" (at zero volts), or "pulsing" (changing it's state quickly from high to low, or vice versa). This information is important, as seen in our working example below. For example, with a logic probe, it can be seen if the CPU chip is "running" (pulsing), or if it is locked in a high or low state.
Unfortunately, a logic probe only indicates state changes (a zero or a one, which is 0 volts to .8 volts, or 2.4 volts to +5 volts, respectively). It is up to you to know if these are the expected changes!
Logic Probes usually have three LED's (and some have a buzz tone too). The 3 LED's indicate:
Using the Logic Probe.
Before starting, the game's schematics are absolutely necessary. So grab those, and open up to the CPU board's schematics. The board has already been checked for proper voltage (it does have a good +5 volts, right?). The logic probe should be connected to a good power source on (or near) the board (on a WPC board, use the driver board power test points).
Turn the game on (make sure the "TTL/CMOS" logic probe switch is set to "TTL") and test the probe by touching the tip to a +5 volt power source on the CPU board. A solid, steady red LED should be seen, indicating high (some probes may also have a tone). On a WPC pinball, I personally like to test pin 40 of U4 (+5 volt power to the CPU chip) for a high signal.
Next probe a ground point on the board. A solid steady green LED should be seen, indicating low state. Again on a WPC pinball example, I personally like to test pin 1 of U4 (ground for the CPU chip) for a low signal.
Now that the logic probe is tested, it's time for some real work! Look at the schematic, and find the RESET pin for the CPU processor. For an example, looking at a Williams WPC CPU schematics, it's processor is a 68B09 at position U4 on the CPU board. The schematics label the reset pin as "RST", which is pin number 37 of chip U4. Probe the RESET pin; the logic probe should indicate a High state (red LED). When the game is first turned on, the reset line should be low, and then go high and stay high. This is pretty much how all reset lines work on any CPU; if the reset line is pulled low, the CPU resets and goes back to being high.
To power off just the WPC CPU board, leave the game's main power switch on, and remove CPU connector plug J210. This will power the CPU board off. With the logic probe on pin 37 of U4, the pin should be low. Replace plug J210, and the CPU board will "boot". Pin 37 of U4 should, after just a moment, go high and stay high.
Simple enough, right? So now probe pins 8 to 23 of chip U4 (any one of those, not necessarily all of them). These are the address lines A0 to A23, respectively. The logic probe should show these pins as pulsing. Likewise pins 24 to 31 are the D0 to D7 data lines. Any of these should show a pulsing signal too. Probing these address and data lines shows that the CPU chip is "doing work", accessing memory and moving data.
When to use CMOS Setting.
A Real Life Pinball Example (more Probing Fun).
Test the Input Side.
To simulate a short to row one of the switch matrix (a fairly common problem), get an alligator clip jumper wire. Connect one end of the alligator clip jumper wire to pin 1 of connector J208. Connect the other end to ground (metal ground strap at the bottom of the backbox). The display should immediately show all switches in row one as closed ("boxes").
Now probe pin 11 of U18 again. The logic probe should indicate low. Remove the jumper wire from ground, and pin 11 should go high again. Now remove connectors J206 and J207 (the switch matrix column connectors). Touch the alligator jumper wire from J208 pin 1 to connector J206 pin 1 (this is column one of the switch matrix). Pin 11 should now have a "high pulse" (pulsing, but still mostly high).
Test the Output Side.
Again touch the alligator jumper wire from J208 pin 1 to connector J206 pin 1 Pin 13 should now have a "high pulse". Also the display should indicate row 1 column 1 (switch 11) as closed (a "box").
Using this input versus output probing technique, failed chips can be found. The only problem in the equation is the repair person must know what the signals should look like in a working game! That's a big problem, but often the schematics or probing a working game can reveal these secrets. Here experience is the best teacher. Working with a logic probe is the only way to get experience.
3f. How to Use It: Soldering a Circuit Board.
What Exactly is Soldering?
The alloy that we know as "solder" is made of various metals. For jewelery, the solder's metals are usually silver and gold. For plumbing and electrical work, lead and tin are usually used. Because we are discussing electrical work, only lead and tin solder will be discussed here.
Electrical solder is usually a combination of 60 percent tin and 40 percent lead (or even 63 percent tin and 37 percent lead). Electrical solder also has a hollow core that contain a rosin "flux".
The flux melts at a lower temperature than the solder itself. Its purpose is to prepare the surface for soldering. It does this by removing oxides from the metals to be joined. It also prevents the heated metals from oxidizing as they are heated. Oxides form when metal is exposed to air. Even "corrosion-proof" metals like stainless steel can oxidize.
When soldering, the molten solder joins metallic surfaces by dissolving into the metals and forming a amalgam (mixture) with them. Often the soldered joint is stronger than the individual components it holds together.
But this mixing of metals can only occur with surfaces free of oxidation and other contaminants. Oxidation can be removed by sanding the parts first, but some chemical cleaning is still needed, since as the parts are heated oxidants can form. The rosin flux is the chemical cleaner.
The rosin flux core in 60/40 solder can normally do all the cleaning necessary on new parts or pre-tinned parts (pre-tinning is the process of adding solder to a part before it is joined to another). But there are some conditions when the rosin flux core is not enough.
The perfect example of this is trying to solder a circuit board that had battery corrosion. Oxides (caused by the battery corrosion) prevents solder from joining with the metals. Oxides also prevent heat transfer. Even a thin layer of oxides can act like an insulator, reducing the heat flow from the soldering iron to the metal(s). The only way to solder a circuit board that had battery corrosion, is to sand the corrosion off, leaving bright and shiny copper traces behind (this also assumes the battery corrosion was first washed with a vinegar solution, to neutralize the battery's base).
When solder isn't sticking to the joint surfaces, it tends to ball-up like mercury. If solder doesn't have anything better to stick to, it sticks to itself. Solder in a bad solder joint can sometimes only be held in place by the rosin flux! Properely soldered joints tend to have a very slight concave appearance. The solder feathers out to a thin film when heated. This happens because molten solder flows towards the heat source. If a joint is clean, the right amount of heat applied, and a good 60/40 rosin core solder used, the solder will flow through the joint easily. Also don't be mislead that "more is better" when it comes to soldering. Too much solder can cause problems too.
Cold Solder Joints.
A Clean Connection.
A Good Mechanical Connection First.
When installing components, bend the component leads so they go straight into the printed circuit board holes. Components should go in gently; don't jam them in as some components can be damaged easily. Don't pull the leads through the board; instead push the component into the board (pulling leads can damage the component). Double check the component's value before installing it. If the component is polarized (many capacitors and all transistors and all diodes), make sure to install it correctly (yes it often does matter which way the part goes!) Most components should be mounted snug against the board. There are some exceptions though. Any component that could run "hot" should be installed with air clearance below the component. Typically this applies to resistors, diodes and transistors. Before soldering the component, double check the value, orientation and position. It's easier to fix a problem now than after solder has been applied.
Examine the Un-Soldered Connection Before Soldering.
"Tin" Your Soldering Iron.
Heat the Joint.
Apply the tapered surface of your soldering iron's tip to the connection being soldered. The tip should *not* be perpendicular to the solder joint, but at an angle (for greater surface area contact of the tip). It's better to directly heat the circuit board pad, instead of the component leg itself (most electronic components are heat sensitive). Allow the joint to become hot (a second or two), then apply the Rosin core solder to the JOINT (not to the iron's tip!). I usually apply solder to the circuit board pad, and solder will spread across the pad, allowing heat to transfer more efficiently across the joint and to the component's leg. After the solder begins to flow, lift the iron's tip away from the joint carefully, keeping the joint stable.
There are some important things to remember here. First, let the joint melt the solder, not the iron's tip itself. Second, keep the joint stable until the solder solidifies. If you fail at either of these two point, you may create a "cold" solder joint (a solder joint that fatigues, cracks or becomes non-conductive later; the term "cold" came about because there wasn't enough heat used to solder the connection). A cold solder joint will not provide a good electrical connection. When the solder solidifies, it should be shiny. A gray solder joint indicates either not enough heat was applied, or the joint moved while the solder was solidifying (making an instant "cold" solder joint that will probably fail later).
Soldering a circuit board with too much heat can "lift" (delaminate) the traces from the circuit board. Traces are the thin metal "wires" that connect the components electrically to each other. These traces are basically epoxied to the circuit board. If you apply too much heat to a solder pad, it will delaminate the pad and it's connecting trace. Though a lifted trace can be tediously repaired, this is the easiest way to ruin a circuit board.
The Right Amount of Heat.
The Right Amount of Solder.
Use cutting pliers and cut the excess component leads. Cut them at about the point where the solder has risen up the component lead. Do NOT cut into the solder mound on the circuit board! This can cause the solder joint to crack later, and fail electrically.
Remove the Flux after Soldering.
Inspecting the Solder Joint.
3g. How to Use It: DeSoldering a Circuit Board (Chip Sockets & Installing/Removing Chips).
IMPORTANT: Keep this in mind when Desoldering!
Always install a new Socket!
Desoldering the "HARD" Way.
Plated through holes are how a circuit board trace gets from one side (of a double sided circuit board), to the other side. They are also used for component soldering. When a component (chip, resistor, cap, etc) is soldered into a PTH, solder files the hole and surrounds/attaches to the part's leg. This makes an incredible bound. If the part is desoldered improperely this bound will still exist to at least some extent. When the user removes the part, the part's leg comes out but the PTH stays attached to the part leg, and is ripped from the board. Now the conductivity from one side of the board to the other side is questionable, even when a new part (or socket) is installed.
Desoldering the "EASY" way.
Note there are some times when you don't want to cut the old part out. For example, if the old chip is needed for some reason, or it is a component that just can't be cut out. But in most cases, a component is being replaced, so if damaged, it is no big deal. Remember, it's the circuit board that you don't want to damage. Cutting out a part that is being replaced anyway is just the cost of repair. Chips are cheap, circuit boards are not.
What to use to Cut off the Old Component.
Another method to cut a chip out is with a Dremel tool and a Dremel cut-off disc. This works great, but is not recommended, especially for the newbie, as a slip of the Dremel could cut traces on the circuit board. Better to use a "flush cutter".
Now that the chip body is out of the way, remove the chip's cut legs, one at a time. Using a soldering iron, heat each cut leg of the chip, and remove it with a needle nose pliers. If a Hemostat (used largely in the medical fields) is available, these work really well for this task too.
After all the pins are removed, use your favorite desoldering tool to clean out the old solder from the solder pads. See the tips below on using a particular desoldering tool.
"Machine pin strip sockets", also known as SIP sockets (Single Inline Package), are a good choice for repairs. Buy them in the longest length possible, and just cut them to the length needed. This way, there is no need to keep specific sized sockets around (just cut them to the length needed). The reason many repair people like them is the ability to see completely around the traces, AFTER they are installed in the board. If by chance a circuit board trace is broken, it can be found much easier.
Another reason many novice repair people like machine pin sockets is the ability to soldered on the TOP side of the circuit board too (though this is not suggested, and should only be done if absolutely needed). If the "plated through hole", which the socket pin goes through, cracks or becomes damaged, the socket may need to be soldered on both sides of the circuit board to maintain continuity from the solder to component side of the board.
Note soldering on the top side of a machine pin socket is only a last resort when there is no continuity between the two sides of a circuit board. Top side soldering can lead to a variety of problems such as increasing the risk of shorts between socket legs, heat damage to the circuit board, and its virtually impossible remove flux because the sockets is in the way. Also machine pin sockets are not designed to be soldered in this manner (often melted socket plastic can be seen where someone has tried to get the soldering iron tip close to the socket pins).
"Dual wipe" plastic sockets are also excellent sockets to use. If the old part was properely desoldered without damage to the plated-through holes, dual wipe sockets are more than acceptable for repair. The important part here is the "dual wipe" part. That is, the inserted chip has metal wipers on both sides of the chip leg. Quality plastic sockets uses dual wipers. This is the only variety of plastic socket that should be used.
Is there any advantages of dual wipe plastic sockets over machine pin sockets? Machine pin sockets hold the chip better, and that's why the military requires their use. But for pinball applications dual wipe plastic sockets are excellent, and there is less risk of chip damage when inserting a chip. Machine pin sockets have a much higher incident of bent "accordian" chip legs upon insertion.
Machine pin strip sockets are available from Mouser at www.mouser.com (800-346-6873). They sell a variety of lengths, and can beut to any length needed. Shorter strips may also be combined into one long single strip too. I personally try and get the most length for the dollar. For example, 32 pin tin exterior and gold interior plating, part number 575-193132 is $0.93. Going much longer than that, and the price really jumps. Another source of this is KCC (Keltron) Connector Corporation in Bohemia, NY (800-346-3532) at www.connectworld.net/keltron/kelt21.html. They have SIP sockets available with standard leads, selective gold plating, and 100 contacts for about $1 each. But you'll need to buy 100 of them at a time, as they don't sell in any smaller quanities.
Most pinball circuit boards are "double sided". This means they have traces on both sides of the board. If a trace needs to go from one side of the board to the other, a "plated through hole" (PTH) is used. When the board was constructed, a hole was drilled in the board, and metal plated on the INSIDE of the hole. This way a trace on the top side of the board can continue to the backside of the board, through this hole. If a component doesn't go through the hole, plated through holes are soldered closed to help maintain their electrical continuity.
The problem with plated through holes is they are easy to "strip out" or crack when desoldering. If a component is difficult to desolder, sometimes the plating inside the hole will delaminate, and pull out with the old component. This means the ONLY connection between the traces on either side of the board is the component going through the hole! If the component isn't soldered on BOTH sides of the circuit board, there may not be continuity between the two traces.
Again the reason machine pin sockets are desirable is their ability to be soldered on both sides of the circuit board. Though not suggested (and really a "hack"), machine pin sockets can be top-soldered if needed. But remember the warnings mentioned above - top side soldering is not suggested and should only be done if absolutely needed.
General Desoldering Tool Tips.
For first time repair people, the Soldapullt tool and a *temperature controlled* soldering station is the best tool to start with. This way the amount of heat applied can be controlled.
The syringe like vacuum Soldapullt tool requires using a soldering station too. In one hand have the soldering iron, and in the other hand have the "cocked" Soldapullt tool. First heat up the solder joint to desolder with the soldering iron. Then put the Soldapullt over the joint at an angle (trying not to touch the soldering iron's tip). Now move the soldering iron away, and quickly position the Soldapullt perpendictular to the board, and quickly press the trigger. This should suck the molten solder from the joint.
Try not to put the Soldapullt tool tip right on the soldering iron's tip. This is not always possible if you're in tight quarters, but practice helps. For instance if desoldering a lead on the underside of a board, put the tool right next to the lead you're heating, but not touching it. Then in one motion pull the iron away and put the Soldapullt straight over it and hit the trigger. It's tempting (and easier) to just do that without pulling the iron away. That will eventually wear the Soldapullt's tip. It's up to you whether to learn the technique or just feed new tips to the Soldapullt over time.
The absolute best technique for removing IC's is to heat against the IC leg on TOP of the board, while holding the Soldapullt against that lead on the BOTTOM of the board. Gently pushing on the IC leg with the soldering iron to center it in the hole while "sucking" is worth bonus points. Then when the Soldapullt's trigger is pressed, it will usually suck all of the solder out cleanly (normal cautions about not overheating an IC leg or circuit pad apply here.)
Note: If a lead is being stubborn, or if your first attempt didn't get all the solder out, here's a tip. Resolder the lead with the soldering iron and some solder. This will give the iron more solder to heat, and the Soldapullt more stuff to pull on when sucking it out. Often, on really fragile or older circuit boards, I will just resolder all the points I am about to desolder, before even attempting to use the Soldapult.
After done "sucking" a solder joint, cocking the Soldapullt blows most of the old solder back out. It is a good idea to open the tool up from time to time and dump out the bits and pieces that hang out in there. Plus, a cake of solder tends to build up on the face of the piston; peel that off too.
Desoldering Stations: Do NOT Use Until it's HOT.
Desoldering Station Maintainence.
All desoldering stations also use some sort of filter to keep the old solder from getting into the air source (this filter is usually located in the solder collection tube). The filter could be as simple as a (100%) cotton ball (do NOT use synthetic cotton, as it will melt!) Be prepared to replace this filter every now and then. Another replacement item is the rubber gasket that seals the solder collection tube to the "Y" adaptor. With time these dry out and fall apart. So it's not a bad idea to have a few of these rubber gaskets around too.
Also many desoldering stations also offer a declogging "toolkit" that includes a set of miniature round files. These are used to clear the desoldering tip and adjacent "Y" adaptor of any stuck solder. It's a good idea to have one of these toolkits too, if it didn't come with the new desoldering station.
Using Desoldering Braid.
To use it, just take a small length of braid, and put it right over the solder joint you want to desolder. Then put a hot and tinned soldering iron on the braid. The braid will heat up, and melt the solder joint below it. The molten solder will be "absorbed" by the braid, leaving the solder pad clean and clear. Do not reuse this section of solder braid; always use a new fresh section for the next solder joint to desolder. Cut the old section off about a 1/4 inch from the absorbed solder (the flux probably melted out of the braid any closer).
Desoldering braid works well, but it requires additional heat to make it work (your soldering iron needs to be hot!) Excessive heat is bad for a circuit board, as it can cause the solder pads and traces to lift from the board. Also adjacent electrical components can be damaged from the heat.
Because this device is essentially a 45 watt iron, I don't recommend it for the first time repair person. But it is an easy desoldering tool to use. Here are some tips:
3h. How to Use It: Summary of Tool source and part numbers.
These are the various models and sources for the above mentioned tools. I list them in my personal order of perference with the best usability per dollar items listed first.
Digital Multi-Meters (DMM)
End of Beginning Circuit Board repair document.
* Go to the Pin Fix-It Index