PINBALL TROUBLESHOOTING
PART 8
TROUBLE SHOOTING TECHNIQUES
By Russ Jensen
Well, what do you know! Many months ago we started a series of articles called "Pinball Troubleshooting" and we are now up to Part 8 and finally getting around to the actual business of "troubleshooting." Well, that's not exactly the case. Before anyone can troubleshoot anything they must be able to understand basically how it works. For this reason we have spent the bulk of this series describing all the basic game components, how they operate, how they are used, and the basic circuits by which they are connected to perform actual game functions.
It is also not true that trouble-shooting has not yet been described. Two very useful and basic techniques, the Zero Ohms Test and the Voltage Drop Test, were described in a previous article. In addition, a simple method of testing relay hold on circuits was also described, as well as other miscellaneous troubleshooting hints scattered throughout the previous articles. In the final part of this series other important fault isolation techniques, and associated test equipment, will be described. First, however, the concept of trouble-shooting (or fault isolation as it is sometimes called) will be discussed.
The first step in fault isolation is to determine what is wrong. To do this you must ask the question, "What doesn't the game do?" This is the first question I ask of anyone who tells me of a malfunctioning game. The answer to that question should provide the clues to the source of the problem. When troubleshooting, all clues are important and should be considered, no matter how insignificant they appear to be.
The next step is to use the clues (symptoms) to help locate (on the schematic first, and then in the game) the circuit components that are involved in performing the game function(s) that are not being properly performed. For example, if the symptom is the game's bonus feature is not scoring properly, the bonus scoring circuitry (relays, bonus step up unit, etc.) is most likely at fault. But if there is an additional symptom in which other scoring (in addition to the bonus) that occasionally malfunctions, you must consider that a malfunction in the basic scoring circuitry (score relay, score step up, or drum unit, etc.) could be interfering with the proper operation of the bonus circuitry. The point to be emphasized here is that all symptoms must be considered collectively in trying to isolate the cause of a problem. Of course, you must also allow for the possibility that more than one (sometimes many) problems can exist at one time.
The next step is to perform organized tests on the suspect circuitry to try to locate the faulty components). The test methods to be described shortly, as well as those described in previous articles, can be used for this purpose. After a little experience you should be able to more easily decide what tests to perform under what conditions.
NOTE: There are two general types of malfunctions, intermittent and sustained. The latter type is much easier to troubleshoot because the failure is always there and all you have to do is systematically track it down. The intermittent failure, on the other hand, represents the most difficult (and sometimes seemingly impossible) type of malfunction to track down. This is true of intermittent in not only games, but any other device for which servicing is required (automobiles, TV sets, computers, etc.). There are two possible situations involving intermittents. Hopefully the problem will eventually worsen and become a sustained problem, thus simplifying troubleshooting. If not, you must very carefully study all clues and try to make a logical guess as to the possible causes of the problem, and check these out one by one.
Game troubleshooting requires certain test tools to aid the "mechanic" in fault isolation. One of the most important of these, the Volt/Ohmeter, was mentioned in "Part 6" of this series, when the Zero Ohms Test and Voltage Drop Test were described. Other simple home made devices will be described in conjunction with the test methods describedin this article.
Test Light Techniques
Probably the handiest tool a game troubleshooter can have is a home made gadget I call the test light. While it is true that any test using the test light can also be made with a voltmeter, the test light is, in general, more convenient and easier to use, because it provides an easy visual indication of the presence of electric power without requiring one to look away from the area being tested to observe a meter reading. I will first describe the construction of this simple device and then present some examples of how it can be used for fault isolation in a game.
NOTE: The examples of various testing techniques will often refer to Figure? (Complex Game Circuit), which was included in "Part 7" (the September and October issues of The Coin Slot of this series.
The test light simply consists of a miniature lamp with suitable socket, with two wires connected one to each side of its two connections, each terminating in an alligator clip a spring loaded electrical clip on connector available at most electronic supply stores). The lamp should be chosen with a voltage rating consistent with the voltage in the circuit being tested. I have found that a 50 volt lamp is suitable for testing game coil circuits with supply voltages between 25 and 50 volts (the lamp glowing at about half brilliance at the lower voltages). For testing 6 volt lamp circuits, a 6 volt lamp should be used. When using any test light one should be keenly aware of the voltages present in the circuits being tested so as not to burn out the test lamp (50 volt lamps are fairly expensive and will be destroyed by 110 volt circuits). For testing these circuits use either a 110 volt lamp or your voltmeter.
NOTE: The alligator clip used should have insulated grips to prevent electric shock when connecting them to higher voltage circuits. The schematic diagram for the game (if you have one) can be used to determine the voltages in each circuit. If you do not have a schematic, a volt-meter should, at least initially, be used to determine circuit voltages.
The purpose of the test light is to detect the presence of voltage at any point in a circuit. For this to be done, the game must first be turned on (and normally a new game started, if possible), of course. If the game shows no sign of being energized, the 110 volt power circuits supplying the transformer's primary must be checked using a voltmeter, and any problem found corrected so that power is supplied to the transformer.
Since most test light testing is done on the game's coil circuits, examples of this type of testing will be given utilizing the typical complex game circuit, illustrated in Figure 7 in last month's article. All references to circuit points by letters will refer to the lower case letters in parenthesis shown on that figure. Similar testing can, of course, be performed on lamp circuits using a 6 volt lamp.
Normally during testing one side of the test light would be connected to some common circuit point (usually a power return line) and the other side moved from point to point to detect the presence of voltage. Since the object of most testing is to determine why voltage is not being applied to one of the loads (coils in the examples to be given) this common point is usually the game's coil common line (point "d" in Figure 7). This can easily be accomplished by clipping one lead of your test light to the coil common side of one of the game's coils. The proper coil terminal can be determined by the color of the wire corresponding to the color code indicated for this line on the schematic diagram.
As you can see from Figure 7, the coil common line in this example is not connected directly to the transformer, but through the fuse and a normally closed switch on the "Tl LT' relay. (In some games utilizing a "GAME OVER" relay, a normally closed switch on that relay would also be in series with this line.) In addition, there are quite possibly one or more intervening quick disconnect connectors in this line.
Any one of these circuit elements could have a problem itself (open circuits or unwanted resistance) preventing the coil common line from getting the proper voltage. So, before you use this line as a reference point for testing, the coil common line itself should be tested.
This can be accomplished by connecting the other side of your test light to the opposite side of the transformer's secondary (point "x" in the Figure). If the light lights you know the coil common line is receiving voltage from the transformer, and hence the fuse, "TILT' relay contacts, etc., are all operating properly. If the lamp fails to light you have a problem in one of those components (or there is no 110 volt power to the transformer's primary). A check of these circuits can quickly be made using your test light. Since this itself is a good example of test light testing techniques, this procedure will be described.
NOTE: Unless the game has a major malfunction, one symptom ofwhich is most of the game's coils are not operating at all, this coil common line would most likely be operating properly, therefore the tests of the circuit to be described would normally not be necessary unless that symptom existed.
Leaving one lead of your test light connected to point "x" (one side of the transformer winding), move the other lead from point "d" to point "b." If the light now lights, you know you have a problem in the normally closed "TILT' relay switch (or possibly an intervening quick disconnect connector). If the light still fails to light, move your lead to point "a" (the transformer itself). You now have your test light connected directly across the transformer's secondary (point "x" and point "a"). If the light now lights, your problem must either be a blown fuse, a bad connection in the fuse socket, or a faulty contact in a quick disconnect connector.
If the light still fails to light, you either have a bad transformer (very unlikely!) or most likely no 110 volt power to the transformer's primary. Get out your voltmeter and check the voltage across the primary terminals, and if none is present determine why and correct the problem. If voltage should be present on the primary, then you have a bad transformer. (In all my work with games I have never found a faulty transformer.)
After you have located and repaired any problems in the coil common circuit (your test light lights when connected between points "x" and "d") you are now ready to use your test light to find further faults in the game.
NOTE: The example used here shows the fuse and "T l LT' relay connected in series with the coil common line. This is not always the case. In some games the coil common line may be connected directly to one side of the transformer and the other coil power line (labeled "x" in the Figure) may be fused and/or broken by the "T l LT' and/or "GAME OVER" relay switches. Consult your schematic to determine your configuration, modify the test just described to suit it in order to determine if your coil common line is receiving power from the transformer. You should also be sure that the coil you use to make your coil common test light connection is one whose common power is broken by the "TILT'(and/or "GAME OVER") relays, if your circuit is so configured.
There are two initial choices that can be made prior to performing a test light test; whether to test from the load up or from the power down. Both methods provide the same end result (finding the source of the problem), the difference being in the amount of time it takes to find the fault. Some examples should clarify what is meant by these two types of testing. In the example to follow it will be assumed that one lead of your test light is connected to the coil common line (point "d" in Figure 7), unless otherwise noted, and that this point has the proper voltage applied to it
Load up testing is generally chosen when you suspect a bad load (burned out coil, lamp or motor). Assume, for example, that the symptom of a malfunctioning game is "10,000 points" are never scored. You might therefore suspect a bad "10,000 step up" coil. To test for this clip the other lead from your test light to point "k" (using the coil terminal) and operate the "10,000 relay" armature by hand so as to close the "10,000 relay" contacts, which energizes the "10,000 step up" coil. At this point three possible results can occur.
First, the coil might be energized and the light will glow, which indicates that that circuit is operating properly. The second possibility is that the light glows, but the coil does not energize. This indicates a bad coil and your problem has been found. The third possibility is that nothing happens, which indicates that either the "10,000 relay" switch is malfunctioning or that an intervening quick disconnect connector (or a broken or loose wire) is the culprit. To check for this, move your lead from the coil terminal to the solder lug on the "10,000 relay" switch, itself connected to the wire of the same color as that connected to the coil terminal you were just connected to (you are still connected to point "k," only at a different place to check intervening wiring and connectors).
Again operate the "10,000 relay" by hand. If your test light now lights, the "10,000 relay" switch is OK and the problem lies in the wiring (including any quick disconnect connectors) between that switch and the "10,000 step up" coil. If the light still fails to light, you would move your lead to the other solder lug of the switch (connected to point "x"). You now have your test light connected across the power supply lines to the circuit If it now lights the problem must be a faulty "10,000 relay" switch. If it still doesn't light, power is not being supplied from the transformer(point "x") to the "10,000 relay" switch (we are, of course, assuming that the coil common line (point "d") has been tested as described previously). You should then check all wiring and intervening quick disconnect connectors between the transformer (point "x") and the "10,000 relay" switch.
NOTE: In the proceeding example, it was assumed that you knew the "10,000 relay" coil was not the problem because it operated when energized and therefore the "10,000 stepup" circuitry was suspect.
Power down testing is generally employed when you have reason to believe that the load itself (lamp, coil or motor) is functioning properly and you suspect one of the switches controlling it to be faulty. For example, lets say you know the "50,000 relay" coild is alright because it energizes when you hit one of the "50,000 bumpers," but the hold on circuit does not seem to operate on that relay. You would first connect your test light to the power supply to that circuit (points "d" and "x"). If the light lights, you know power is being supplied to the circuit
The test light lead originally connected to point "x" should now be moved to point "f." If the light still lights, you know "Motor Switch 5A" is operating properly. If the light fails to light that switch is either not making good contact, or there is a problem in the intervening wiring or connectors.
If the light lights when connected to point "f," move your lead to point "e" and operate the "50,000 relay" by hand. If the light now fails to light, the problem must be in the "50,000 relay" hold on switch (or intervening wiring or connectors). NOTE: As was pointed out earlier in this series, all points on the schematic, such as point "e" in the above example, actually have two or more connections in the game (i.e. both ends of the wire plus any terminations at intervening quick disconnect connectors). Point "e" terminates at both the "50,000 relay" hold on switch and the "50,000 relay" coil. If current is found to be present at one of these points and not the other, a problem must exist in the intervening wiring or quick disconnect connectors This is a very important point to keep in mind and often overlooked by inexperienced troubleshooters.
The examples given above should give the reader the basic ideas of test light troubleshooting. Once one becomes familiar with these techniques, he should realize that they are a quick and easy way to track down most game malfunctions.
Before leaving the subject of test light testing two points should be made. Several times during the above discussion I have referred to operating relays by hand. By this I mean pushing the armature against the coil (or tripping by hand a latch-trip or relay bank relay), so that the switch(es) on that relay will operate. In the above examples only one relay was involved, but sometimes it becomes necessary in testing a series circuit to operate more than one relay simultaneously. In these cases you may want to short out a switch using a clip lead (more about these later) rather than physically operating the relay. To do this, you would simply clip the two ends of the clip lead to the two solder lugs of the switch you wish to close.
NOTE: The clip lead method is fine when you just need to operate one normally open switch on a relay, but you should keep in mind that other switches on that relay (and the normally closed side of a single pole double throw switch) are not operated by this method, which could cause abnormal circuit operation. An alternate method would be to place some object between the top of the armature and the metal stop (which keeps the armature from coming up too far when the relay is not energized), such that all switches of the relay are operated as if the relay were energized).
The final point to consider is the major weakness of test light testing. Testing circuits using a test light is similar to the Voltage Drop Test, described in a previous article, with one major difference. In the Voltage Drop Test the actual voltage of each point in the circuit is measured rather accurately. In test light testing the light merely gives an indication of the presence or absence of a voltage. If the voltage is less than it should be, the lamp will glow somewhat dimmer, but it will take possibly a 20% decrease in voltage before most people might notice the difference. The point to be made is, even if the lamp test seems to indicate that a circuit is operating properly, if problems still exist double check that circuit using your voltmeter.