PART 8 CONTINUED
TROUBLE SHOOTING TECHNIQUES
By Russ Jensen
Clip Lead Testing
One ot the simplest, and almost foolproof methods of troubleshooting game circuits utilizes a simple clip lead (sometimes referred to as a jumper wire). This is used to by-pass suspected circuit elements, in a systematic manner, in order to locate faulty components. As early as 1937. Bally described this method quite well in a small pamphlet provided with a game called LINE UP (and most likely others as well).
The only tools required to perform this test is one (or occasionally more) clip leads. A clip lead is simply a length of electrical wire terminated at each end with an alligator clip (see the previous discussion the November issue of the construction of the test light). These leads can be purchased at most electronic supply stores or home made. I have found it very convenient to have one clip lead at least three feet long that you would almost have to make yourself.
The basic principle of this method of testing is really quite simple. One end of the clip lead is connected to the power source and the other end used to apply power directly to various points in a circuit. This. In effect, bypasses all circuit elements between the power source and the location where your clip lead is connected.
Generally, the lead would first be connected to the load (lamp, coil. or motor) in the circuit being tested (the other end of that lead must, of course be connected to the proper power source for that load: six volts, coil voltage, 110 volt line. etc.). If the load now operates, you know it is good, and the problem is in either a switch or wiring (including connectors) that have been by-passed by the clip lead. If the load fails to operate it is the problem.
NOTE: It is assumed you know that the power source to which your clip lead is connected is providing the proper voltage, and that the other side of that power source is supplying power to the common line to which the other side of the load is connected. If there is any doubt about this you should first test for voltage between these two points using a voltmeter or test light.
If the load operates when connected to the power source via the clip lead, the next step is to move the clip lead back one point in the circuit 'unbypassing' one of the switches in the series circuit, if that switch (or parallel combination of switches) has a normally closed function the load should still operate. If the switch is normally open it must be closed by hand first. If the load still operates you know that switch is operating properly, and the problem must be in the rest of the circuit that is still bypassed. If the load does not operate, you have isolated the problem to the switch (or switch combination) just 'unby-passed' (or any intervening wiring or connectors).
NOTE: If you are dealing with a parallel combination of two or more switches, each switch must be operated by hand separately to insure that all are operating properly (each should energize the load when Closed). If any of these parallel switches are normally closed all of these should be first opened, as any closed switch in a parallel combination will operate the load such that the other switches) cannot be tested. A simple way to open these switches is to place a piece of paper between the two closed mating contacts, pulling the paper out to again close the switch. Remember, only one switch in a parallel combination should be closed at a time during testing of that combination.
You should continue to move the clip lead back one point in the circuit at a time, (closing all normally open switches in the circuit between the point to which you are connected and the load) until you find a point where the load fails to operate (when all switches are closed). At this point you have isolated the problem to the switch (or parallel combination of switches) you last 'unby-passed' with your clip lead (or any intervening wiring or connectors). You should then check these elements to find the problem. The Zero Ohms Test, described in a previous article, or the Continuity Test. to be described shortly, are good test methods to use for this purpose.
NOTE: If intervening connectors are present in the circuit, you may consider them as series circuit elements (equivalent to a normally closed switch) and test them by clipping your clip lead first to one side of the connector pair of mating contacts and then to the other. If the load operates in one case and not in the other the problem must be in the connector.
An example, Figure 7 from the article in the October issue, should serve to clarify the test method just described. Suppose you wish to test the energizing circuit for the "10,000 Relay." You would first connect your clip lead to point "x" (assuming you have already determined that the full coil voltage is present between that point and the point "d" coil common line). The other end of your clip lead should then be clipped to point "g" (the coil terminal on the "10,000 Relay" not connected to coil common). If the coil now operates (i.e. the relay pulls in) you know that the coil is all right; if not, your problem is a defective relay coil.
Assuming the coil is found to be operational, you should next move your clip lead from point "g" to point "h“ on the switch stack of the ‘50,000 Relay." Since the switch involved in the circuit on that relay is normally open you must next close it by hand. If the "10,000 Relay" now operates you know the switch just tested is operating properly. If not, your problem is either in that switch or in the wiring between that switch and the “10,000 Relay" coil. The latter possibility can quickly be eliminated by moving your clip lead to the other solder lug on the switch you have just tested (which is also point “g"). If the"10,000 Relay" now operates the problem is definitely In the switch. If it does not operate there is a problem in the point "g" wiring between the "50.000 Relay" switch and the "10,000 Relay" coil.
Now, assuming you have determined that the “50,000 Relay" switch is operating properly, your problem has been isolated to the "Motor Impulse" switch (or the point "h" wiring between it and the "50,000 Relay" switch).
This wiring can, of course, be checked by moving your clip lead to the solder lug on the "Motor Impulse" switch, which feeds point "h," and closing the "50,000 Relay" switch by hand. If the " 10,000 Relay" coil does not operate the problem is in the point "h" wiring (including any connectors).
The testing just described tests the "50,000 Relay" energizing circuit for the "10,000 Relay" coil. Similar testing can be performed on its hold-on circuit (utilizing point "j" in lieu of point “h"). This example, plus the general principles previously described, should give a person a reasonable idea of how to apply this useful testing technique.
"There are three types of tests
for which continuity testing is quite
useful because it gives a quick
visual identification as to whether
or not a closed circuit exists."
The final testing technique to be discussed is called continuity testing. Continuity testing is, in reality, another form of the Zero Ohms Test (described in a previous article), only using a visual indication from a lamp in lieu of reading an ohmmeter
For this reason no specific examples of actual circuit testing will be given here as the reader can refer to the discussion of the Zero Ohms Test. The test device itself will be described followed by a discussion of a few instances where the use of continuity testing is sometimes desirable over the use of the Zero Ohms Test
NOTE: When continuity testing is used in lieu of Zero Ohms Testing one important point must be kept in mind. Zero Ohms Testing actually performs two functions that are related. One is to detect open circuits (infinite resistance) and the other to detect unwanted resistance. The continuity test, for all practical purposes, can only detect open circuits since the presence of unwanted resistance (unless that resistance is fairly high) would only result in a small decrease in brilliance of the test lamp, which normally could not be noticed by the eye.
The continuity tester is actually a simple series circuit consisting of a battery (power source) and a lamp (load) with two clip leads to complete the circuit To construct one you need a lamp (with socket), a suitable battery(ies) with some means of holding them (and connecting the batteries in series when more than one is used), and two wires with alligator clips on one end of each wire.
The lamp chosen should be either 1 1/2 or 6 volts A 1 1/2 volt lamp requires only one 1 1/2 volt flashlight battery, a 6 volt lamp requires four such batteries connected in series (that is the positive terminal of each battery connected to the negative terminal of the next, etc., leaving one of each type of terminal available for external connection). Battery holders made to hold four batteries and connect them in series, are available at most electronic supply stores.
One terminal of the battery (or series string of batteries) must be wired to one connection on the lamp socket. The other battery terminal and the other lamp socket connection should each have a wire, terminated by an alligator clip connected to it When the two clip leads are then touched together a complete circuit should be made thus lighting the lamp.
NOTE, ready-made continuity testers can be purchased at some electronic stores. If you decide to buy one, get one that uses batteries and an incandescent lamp. Some solid-state units are available but these should be avoided, as they will indicate continuity even though a coil might be in the circuit. An incandescent lamp will generally glow noticeably dimmer if you're in series with a coil so you know you do not have a circuit of zero ohms or there-abouts. Some testers use batteries and a buzzer (in lieu of a lamp). These will generally be acceptable but less desirable.
Before discussing the uses of the continuity tester, a word of caution should be given. As was the case with the Zero Ohms Test, all continuity testing must be performed with all power off on the game being serviced. This means that the machine should be unplugged from 110 volt house current before attempting any continuity testing.
There are three types of tests for which continuity testing is quite useful because it gives a quick visual indication as to whether or not a closed circuit exists. These are: wire tracing, testing of quick disconnect connectors, and testing of switches (on relays, etc.). Always keep In mind, however, that the continuity test only gives an indication of an open or closed circuit and Is not a reliable substitute for the Zero Ohms Test in detecting unwanted resistance. In this same light, it should be pointed out that if continuity testing seems to indicate that a circuit is alright, but that circuit still does not seem to function properly, use the Zero Ohms Test to check for unwanted resistance in that circuit
Wire tracing is checking a wire, either run directly or through one or more quick disconnect connectors, to determine if it has continuity (i.e. makes a complete zero ohms circuit). The wire to be traced will have the same colors) wherever it appears in the game, even though it may pass through one or more connectors, One should beware, however, that some color code combinations are used for more than one wire. For this reason you should make sure that each circuit point you test is connected to the wire you are testing by making reference to the game's schematic.
NOTE: The wire we refer to may actually consist of more than one physical length of wire, as long as each of these wires is electrically connected together at solder terminals or by quick disconnect connectors. A wire Is represented on a schematic by a line connecting two or more circuit elements together and may have several branches as long as there are no intervening circuit elements other than connectors.
Before beginning any continuity test, check your tester by touching the two clip leads together causing the lamp to light. Now connect one clip lead to one connection point (solder lug on any component connected by the wire being tested) of the wire. Touch the other clip lead to each of the other connection points (circuit element solder lugs) for the wire being tested as shown on the schematic If the lamp fails to light when connected to any of these points an open circuit exists somewhere in the wire being checked.
If, when your lamp fails to light, the two points you are connected to are in different areas of the game (i.e. one end in the backbox and the other on the playfield) then the wire you are testing goes via one (or more) quick disconnect connectors, which could be the source of the problem. To check for this remove one of your clip leads from its connection point remembering where you had it. Now go to the connectors in the game area where your other lead is still connected and look for a connector terminal with a wire connected to it of the same color(s) as the wire being tested.
Next, touch the free clip lead to the solder terminals for that wire on each of the mating connectors. If the lamp lights each time, the connector is fine. If the lamp lights on one side of the connector only, the connector must not be making a good connection. If the lamp does not light on either side of the connector, there is either a problem somewhere else in the wiring, or you are testing a different wire on the connector with the same color(s), so look to see if there are any more wires on the connectors in that area with the same color(s) and test them also
The above discussion should give one the basic principles of wire tracing using the continuity tester. Once an open circuit is found you must next determine the cause. It could be a connector (as just described), a loose wire (unsoldered from a terminal or a poor solder connection), or even possibly a broken wire (the conductor severed inside the insulation). The latter condition is rare but I have seen it several times. Once the problem has been isolated to a particular section of the wire you must systematically check for all possible causes
Another common use for the continuity tester is to test a particular set of switch contacts or a pair of mating elements of a connector. In both cases the two clip leads of the continuity tester are connected to the two solder lugs of the switch, or pair of connecting elements of a connector that you wish to check In the case of a connector, or a normally closed switch, the lamp on the continuity tester should glow indicating the element being tested is alright if the lamp glows dimly (dimmer than when the two clip leads are directly shorted together), or not at all, the element being tested is making a poor connection (unwanted resistance) or no connection at all (open circuit). If you are testing a normally open switch you must first close the switch by hand before the lamp will glow.
This completes the discussion of continuity testing (and all testing for that matter). As was implied previously, continuity testing can be used in lieu of Zero Ohms Testing to test for complete series circuits. Remember, however, the warning (which applies to all tests using lamp indications in lieu of a meter) that if the circuit being tested seems to check out, but still does not operate properly, double check using your meter.
Whew! This is it! What I originally envisioned as a two or three article series on pinball troubleshooting has ended up in eight parts, taking twelve issues to publish. What happened, actually, is that I just can't knowingly leave anything out I try to tell everything about everything, which of course is impossible, but I gave it a shot
I have tried to gear this series primarily for the person who has never worked on a game before. This is why I spent a lot of time describing game components in detail and very basic electrical circuit theory. I hope, however, that some of what I have said can also be of help to the more advanced troubleshooters as well, since much of it has come from things I have encountered in working with games over the years.
I have also tried to make this series applicable to both old and more modern machines., The basic circuit theory is the same, of course, and many components are almost identical, the later ones being a little more sophisticated perhaps and possibly better designed. The basic components (relays, stepping switches, etc.) have actually changed very little over the years, other than in the construction.
Before closing one important point should be made. There is no substitute for experience! I am constantly amazed at the new things I discover while working on games. New troubleshooting techniques are developed by necessity when trying to solve a particular problem. New circuit configurations are discovered when working on some more sophisticated game circuitry (those pinball designers were no dummies). You never stop learning. That old adage, "experience is the best teacher" is certainly true when it comes to pinball troubleshooting.
What! No Game?
What if you don't have a malfunctioning game to work on right now? Here are a few suggestions on how to make the information presented in this series more relevant First, copy all of these articles and bind them together like a booklet Next. Read them over again trying to absorb more from each subject When reading descriptions of components, open up a game and look at a typical component as your read the description. Operate It by hand when ever possible. When reading descriptions of circuit configurations, get out a schematic and find a similar circuit. Try to follow the actual circuit while reading the description. You may also perform tests (Zero Ohms Test, continuity, clip lead, test lamp, etc.) on operating circuits to gain familiarity with performing those tests as well as seeing what the indications should be on a properly Operating circuit.
These techniques should greatly help to strengthen your understanding of this subject until you have the opportunity to troubleshoot a real game problem. Good Luck!
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