“Don’t troubleshoot unless you need to”
There are many websites and documents out there explaining how to repair EM pinball machines. I did not want to just repeat what has been said. My hope is that this document will help shed some light on functionality to allow you as the repair person to diagnose and repair more complex problems. I want to shed some light on the actual function and what is really happening when the relay is closing or the score motor is running. This document assumes that you have cleaned and adjusted all your contacts, if not stop and do this if you implement anything in this document you will be chasing your tail, a pin that has been sitting around for a long time will have many issues and to apply these troubleshooting techniques to every problem that can be found in an em pin that has been sitting around unused for ages will take way too long. Do yourself a favor and just clean and adjust first and read those other articles first.
Now then you have done the above and you have a lingering problem or two. You will now need a schematic for the machine you are working on as long as it is not a Gottlieb you can usually find it on IPDB – Great resource.
“Look at the trees not the forest.”
Don’t get overwhelmed with the overall seemingly complex array of switches, when you are troubleshooting only one problem, it will usually boil down to 3 or 4 switches. The key is to get on the right track and to correctly identify the circuit that is having the problem. You solution will fall into a narrow range of categories either mechanical, contacts, or timing. Timing is the most complex problem to troubleshoot I may write another article about this later.
“Score motor, or heart beat”
The score motor is more of the heart beat of the machine activated when a multiple step process needs to be triggered. Yes it does allot of scoring but it also will activate features change the ball served, process stored credits. Anything that needs multiple step processing or resetting. On most all schematics the score motor contact will be enclosed in a circle. What is less clear on the schematic is how many times that switch will pulse In one revolution, this can be important to know, especially if you are troubleshooting timing issues. In most cases the score motor only needs to turn one whole revolution to complete a cycle. If you have a score motor that is turning two or three times to complete a process you may have an issue.
“Meat and potatoes”
Ok now I want to talk about the process in detail. When some event is triggered a corresponding relay should close. And stay closed until some other process has completed even after the event that triggered the relay has reset or switch has opened up again. The process does not have to be completed at the time the relay closed. The relay must remain closed until we are sure the mating process has completed. Every relay is like this it will have a contact that will hold it’s self closed. You will notice on the schematic the contact that is the self hold contact, other usually normally closed switches will be in line with this contact to release it once the process has completed if there is a secondary triggering process you would see a n.o contact in line with the self hold contact. If you have a stuck relay or one that will not hold down check this circuit path out, I will explain how to do this later. Another way a relay can stick is if the activating process which will run parallel to the hold process has not released. Parallel circuits can be hard to trace but there is a simple trick to see if it is on the lock hold side holding the relay down or the activating side, simply pull up on the relay it should break the self hold and stay up, but if it closes again then the circuit that is holding it closed is the triggering circuit; witch normally but not limited to a switch on the playfield somewhere. Scoring relays in the back box will have this same self locking contact, even though it will open up as soon as the score has been added. This is because the relay needs to remain closed long enough for the score reel solenoid to push all the way in. That is where an E.O.S (end of stroke) switch comes in. The EOS switch in most cases will be a normally closed contact that when the coil activates will open up causing the lock hold on the activating relay to release, this ensures the process will complete properly. If you have a stuck scoring relay the same trick can be used, if you pull up on the relay and it closes again then the switch triggering the relay is stuck like a playfield switch activated by a ball. But if it stays up you can bet it is a problem with a score reel eos switch or related issue with wiring/mechanical movement in the self hold path.
There is one way that you can get yourself confused when troubleshooting these circuits, I did it in the beginning. Make sure the machine is on and in play on a ball. Game over and tilt will cause many relays to de energize regardless of their locking problem. The game over and tilt relays will be in line with the supply side (opposite of the switches and control side) and will de- energize many locked solenoids and relays. I recommend removing the tilt bob. Jostling around in there you may accidently tilt the pinball there by screwing up your diagnostic process.
In some cases you may find a solenoid or relay that will not have a lock hold directly on the relay, be assured that all relays need some event to open it back up again, either through a stepper or some other process. Remember a relay must remain closed long enough for the intending process to complete, the lock and holding process may be more convoluted but it will be there.
“Resisters and relays what is this all about”
On some relays you will see a resister in the lock hold circuit, (if a capacitor is involved it may be a timing circuit so this will not apply) the resistor will lower the current flow through the coil of the relay causing it not to heat up as much. Relays require much more current to pull in but once it is in it can remain closed with much less current thereby keeping the coil cooler. You will see these on relays that are expected to stay closed for very long periods of time. If you see one of these pulled in for a long time it probably is not a stuck really. This brings me to another point not all relays will be open even when the game is over. The hold really is a good example of this. Generally this will remain closed as long as the machine is on. The purpose of this relay is to control the kick off circuit and the left flipper button on circuit. The lock hold part of this circuit will go to a pin in the bottom of the cabinet that when kicked will drive a pin up and open a set of contacts holding the relay on. And the trigger part will be the left flipper button pressed. If you are trying to understand the locks hold circuit this is the easiest circuit to analyze on the schematic to see how the lock hold design works.
“I don’t have any stuck relays but it still is not working right”
First locate the switch that is to start the process usually on the playfield somewhere, Do you hear a relay click ? – if so watch for this relay and see if it holds down. If you don’t have a click the triggering circuit or the coil it’s self could be bad or there is another contact that must be closed before that relay can close. Check the schematic and follow all the switches in line with the one you are activating. If there is only one in line with it then you either have a bad coil, wiring, switch problem on the activation side of the circuit. Quick check to see if the coil is bad is to press on the relay and manually close it activating the lock hold, if it holds down the coil is good, you have a broken wire or bad contact somewhere. If it clicks and releases without a completing process suspect the lock hold side.
Ok now that we have identified which path we need to check. Time to break out the volt meter. Put it on ac volts and connect one lead with the alligator clip to the coil common side, you will notice this because it will be a wire looping to all other coils. If this circuit passes through the score motor pull the service plug so the score motor will stop thus preserving the switch states as they are, (don’t forget to plug this back in when you are done) This is very helpful when troubleshooting in this manner. We are now looking for good 25-50 (depending on brand of machine) volts on you meter. When you connect to the other side of the coil 10 volts 15 volts don’t cut it, this is just a reminder that you have a problem. If you are on the lock hold side start measuring voltage at every contact in line with the lock hold contact till you see a good voltage, once you see this you have just passed the point at which your problem is located, go back one contact and clean adjust even jump across it to see if you can get a good voltage to the next wire. The same process is true for the triggering side but you will need to hold the triggering switch closed with something so you can track that voltage back from the switch to the relay coil. Once you have identified the switch that is causing you your problem check to make sure the wires are soldered on good and no other wires are touching. After going through this process don’t be too quick to pass on this switch even if it looks good. You are there you found the fault, if you did everything right and you trust what you did look very closely and pull on the wires to see if they break off easily or if some unseen scum is on the contacts. I have seen strange issues at very good looking contacts. You may end up replacing the set of contacts at the worst case.