Hi everybody, I could use some help figuring out a display problem on my Totem machine. Immediately when I power on the pin, the player 3 & 4 displays shows all ones (111111). I've taken a picture of this and attached it to this message. I've moved the score boards around - swapped 2 & 4, and 1 & 3, and the problem stayed in the same place. I've disconnected one score board at a time, and the problem persisted. So it seems the problem is either in the main board, or the connectors from the main board. I've cleaned all of the edge connectors and re-terminated all of the pins in all of the connectors on the main control board. So now I am thinking I have a problem on the main control board. Everything is fine when I run diagnostics. If I play a 4-player game the displays will begin to operate normally. But up until that point, I get all 1's.

This pin has a Rottendog power supply, and I've moved the battery backup off the main board. Also, after the game boots the credit display shows something funky - in the photo it looks like a 4 with the bottom segment of the 4 missing. That display is fine - there are not four credits in the machine, it's garbage data.

Has anyone seen this problem before? Does anyone know the cause? I want to fix this problem. Thanks much.

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Thanks for the tip on the credit display, I'll investigate that.

I swapped the 3 & 4 displays with 1 & 2, and the problem remained with the 3 & 4 displays. So it appears the problem is not related to the displays themselves.

I have already repinned all of the connectors on the A1 board. I did a continuity test between all connectors on A1J2 and 3A4J1 and everything is fine. I also made sure chips Z16 and Z17 do not have the 5v pin shorted to ground. I agree this is a "Segments Group B" issue on A1J2.

I decided to trace the problem back from the display. On the display board, chip Z1 (UDN6118A) pin 11 drives the "1" segments. At power on I get 127 V AC there. I see 130 V AC on pin 10, which is the supply voltage. Pin 8 is the input for Pin 11, I get 2.5V DC on pint 8 at power on. This voltage begins to decline, and after a few minutes drops to almost zero.

I traced this back through the connector. On board A1 this is pin 19 on A1-J2 - Segments Group B. But pin 19 isn't driven from one of the 7-segment decoders Z16 or Z17. Pin 19 is driven from Z15, which a 4-input AND gate. Testing that chip, I see the same behavior at power-on. Pin 6 on Z15 immediately gives me 2.5 v at power on, then it slowly drops over time. The four inputs are between 1 and 4 volts. Since at least one input is below 2 volts the output should not be turned on. So I think Z15 is bad.

But here is where I get confused - the output on Z15, pin 6, is also connected to an inverter and a cap and then goes to pin 4 of Z17. So it's possible something along that line is failing, pulling up the voltage at the output of Z15. Does anyone have experience with this? Do 4-input AND gates fail this way, or does someone have another suggestion? I'll resolder Z15 if I have to, but I don't want to start pulling chips off that board willy-nilly, for fear of making things worse.

Z15 was bad! I replaced the chip and my displays are working fine now. Thanks for your help. Incidentally, when I tested Z15 in a breadboard it operated normally. Clearly that isn't a valid method for testing these TTL chips.