I'm working on a Terminator 2 that had a driver board with some nasty issues. The tie back wire on the drop target coil broke off and Q20 along with the diode and resistors in that area burnt up pretty good. It also took out the 74LS374 at U2 which was causing 3 different coils to not work. I got that all fixed up and all the coils are working as they should.

The problem I'm having now is the cabinet flipper switches do not work in switch test, which in turn is causing the flippers to not work (power is good at the flipper coils). All the other switches in the game work fine. Since this is a pre-Fliptronics game, those two flipper switches go thru the 4n25 opto isolators on the driver board. I tested both of the isolators with the instructions on pinwiki and they test fine. I know the MPU board is good as the flipper switches register if I manually test them with a jumper wire.

I tested the wiring from both cabinet flipper switches back to the driver board and it's good. I've also tested the connection from each pin on the opto isolators to their corresponding pin on the MPU board and that's good as well.

At this point I'm thinking that perhaps the opto isolators are testing fine but failing under load. I don't have any and my local parts shop is closed until Monday but thought I would ask to see if there is something else I'm missing that could be causing the issue. Thanks.

Ok made some progress. If I put a jumper across W4 and W5 on the driver board (bypassing the relay) then the left and right flipper switches work in switch test and the flipper coils fire. So that tells me the opto isolators are fine. I swapped the 2N5401 at Q99 (even tho it tested fine) and the flipper relay will still not engage. I never hear it click.

I'm thinking either the flipper relay is bad or there is an issue in the circuit that drives it.

So another update on this. I was also having issues with the GI not working at all. The connectors had all been fixed but I was only seeing around 2v AC at the outgoing GI pins on the driver board (voltage was good coming into the driver board from the transformer).

I thought perhaps the 74LS374 at U1 might be bad as that is in the flipper and GI circuit. I pulled it and tested it with my IC tester and it said it was fine. I installed a new one anyways and now all my GI works! Apparently that chip was failing under load.

Unfortunately the flipper switches are still not working. I’ve got 5v at R208, I tested the diode at D39 and it’s good and I swapped out the 2N5401 at Q99.

At this point it looks like the relay is bad as I can’t see anything else that would be causing the flipper switches to not work, especially since they work fine if I run jumpers on W4 and W5.

I'm seeing 38 ohms on the flipper relay coil (with the meter leads in either direction). I swapped out Q99 (2N5401) again along with D39 but still not working. I've got 5v at the emitter of the 2N5401 but nothing at the collector. Traces are good for everything in that circuit as well.

All that's really left is that relay. I've got one on order so we will see if that does the trick.

For signal T7 at IC1 pin 12, it's high when not in a game and lo when I'm in a game. The odd thing is that if I play a game, the flippers will work but sometimes the GI will flash when you hit the flippers and when that happens the flippers go weak for a quick moment.

In test mode, the cabinet flipper switches or the flippers will not work at all and the GI goes completely out. When you exit test mode, the GI lights come back on.

I'm not 100% positive that the relay is bad but everything is pointing to that. A lot of the time while I'm playing a game, the GI will cut out (meaning goes out completely and then comes back on and does this very quickly) when I engage a flipper and the flipper will go weak in correlation with the GI cutting out.

When I go into test mode, all the GI immediately goes out completely. When I go into the GI test, I can run the dimming test for each of the 5 sections of GI lights and that works fine but when I run the dimming test for all the GI, none of the GI lights up at any of the intervals.

Also, when I go into the all lamp test, none of the lamps light up and flash like they should. But if I test each individual lamp they light up and flash individually just fine. Never seen anything quite like this before.

Pin 1 on U1 stays low in and out of GI test and lamp test.

The display does not flicker when the GI flickers and the flipper goes weak. The flippers only go weak when the GI flickers and they immediately have full strength after the flicker.

Ok so in and out of GI test and lamp test, I'm seeing the following on U1:

Pin 3 - high
Pin 4 - pulsing high
Pin 7 - pulsing high
Pin 8 - pulsing high
Pin 11 - pulsing high
Pin 13 - pulsing high
Pin 14 - high
Pin 18 - high

It's so weird how the flippers will not work in switch test but they do when playing a game and in video mode as well.

FYI I did replace the flipper relay but no change.

I went to a friends house tonight that has a T2 and we tested my MPU board in his machine and it was doing the same things so the problem is definitely on the MPU board. We used his ribbon cable as well.

Tomorrow when I’m back at the shop I’ll dig into the MPU. This one is a Rottendog board unfortunately. I’ve never had good luck with their replacement boards.

Ok so I did some checking on U12 on my Rottendog MPU board. All the input pins are pulsing high/low but the following output pins are high and not pulsing: 5, 12, 14 and 18. Output pins 3, 7, 9, and 16 are pulsing high. The Rottendog MPU uses a 74HCT240N at U12 and I don't have any HCT chips, just the LS chips, so I'll have to order some.

Yeah I was going to try the LS version as I thought I had some but I didn’t. It wasn’t socketed on the Rottendog board. I desoldered the chip and tested it with my cheap chip tester and it tested fine but I’ve had chips test fine with this chip tester only to fail under load.

I’ll report back once I have the replacement. Thanks for your help!

I installed a new 74LS240 at U12 on the MPU board and that fixed the remaining problems with the flippers and the GI. Thanks again schwaggs for all your assistance! It's greatly appreciated.