Gottlieb 80b:

While trying to diagnose the most bizarre of needle-in-a-haystack issues I've ever come across, I was checking all the voltages coming from my transformer. All the DC voltages are close but not exact. ~6.5v where it should be 6v, ~6.8v where it should be 6.3v. All the AC voltages are much lower than the schematic lists: ~12vAC where it should be 24v, ~16 where it should be 27vAC.

All fuses are good, transformer ground mods have been done. What is the problem?

At the jumper on the transformer which receives 110vAC from the power cable (wall>cable>power line fuse>transformer jumper), the pins which go to the transformer itself and to the service outlet both read ~117-118vAC. Both 110vAC Return pins read ~0.3-0.4vAC

The original problem involved eight controlled lamps which would run at (~)half power. Eight spread across three different latch flip-flop IC's (four on one [Z8], three on the next [Z9], one by itself [Z11]). All three IC's tested fine. Every once in awhile the 8 would come back on to full power, but only briefly. Sometimes, they'd stay at full for what seemed like 3 minutes (during game play) but usually once the game went back into game over / attract mode, they'd go back to half power. For sure every time the machine was powered on, they'd be at half power even if they were holding at full when the machine was turned off.

The eight lamps would also dim further when the ball release solenoid would engage. Another strange thing is the three faulty lamps controlled by Z9 which stay completely lit until their corresponding target is hit, would fluctuate in time with the blinking of the faulty lamp from Z11 when it was blinking. The speed of the blinking increases based on the level of the "play field multiplier" feature, and with it the Z9 lamps would also increase their fluctuating speed.

Different things would cause them to come on to full, but most often full-power could be produced by manually holding the left flippers up (so the NO EOS would close) and tapping the left flipper button repeatedly, sometimes holding the button for a little bit and then a couple taps.

If you notice, I am talking about this all in past tense because just today the problem (knock on wood) has seemingly ceased. I had the play field up to get in to the cabinet, started a game and tried the "left flipper rapid button push" trick I mentioned. It eventually brought the eight lamps to full so I let it just sit for a bit to see how long until they went back to half if nothing else was happening (because usually they would go back to half after no more than 30sec). They stayed on full. I let it sit for maybe 4 minutes and then put the play filed down, added the balls, and played a game. They stayed on full. One-by-one, I tried everything I could think of that normally would put them back to half power. They stayed on full. Eventually I let the game end because game over / attract mode almost surely always put them back to half power. They stayed on full. I held my breath and cycled the power. They came on full. It's been all afternoon, I've played several games, turned the machine off and on, and they are holding at full.

The worst (pinball related electrical) problems are the ones which fix themselves because you can never be sure what caused them in the first place.

The big issue which has started this all is no more, but there are still little things like light taps of either flipper button briefly sends a little power to some of the flashers or heavy/rapid use of the flippers causes a ever-so-slight dip in the brightness of the GI. Little by little....

I'll take pics.. one moment

Two pics showing the pins (1 and 3) receiving what should be 110v, two pics showing the AC return (pins 2 and 4), two pics trying to just show the jumper. The three ground jumper wires are in the correct placement for 110v operation (according the the manual)

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I have done the main ground mod as demonstrated in Todd Tuckey video. As far as grounds for the boards, the CPU is a Swemmer board and the driver is a Ni-Wumpf. I have them connected with a 40-pin ribbon cable, so they have the grounds and the Ni-Wumpf has a ground lug which I have connected to a main ground strap.

Also, two-wire jumper next to the main 12-pin in the photo should have 115vAC on both wires and they read ~30v and ~1.4v.

Ok, just double checked the first jumper I mentioned at the top of this thread, guess I was mixing numbers and ac / dc before.

27vAC send and return both read 16.222v. 6.3vAC send reads 3.22v, return reads 4.77v

I did have one lead on ground when measuring the AC. Let me go check again with out the ground.

...you learn something every day.. Thank you GRUMPY. Still reading 118vAC from the wall outlet. Where the transformer should be putting out 27vAC, it is putting out ~29. Where it should be 6.3, putting out ~7.1.

Are these acceptable ranges to be over?

All were going bright/dim together. And also as mentioned, when one would be blinking as it was supposed to, 3 of the others would dim in time with the blink (which were supposed to remain lit). Of all the testing I did, I am pretty sure it wasn't a purely physical thing, but somehow electrical.