been trying to track down this problem for months (i am strictly an amateur). displays would flicker and eventually died altogether. i replaced the filter caps and C6 on the power supply. repinned the connectors and added additional grounds. no longer blowing the 69v fuse. cleaned up an accidental solder bridge, replaced a couple of blown diodes (CR3/CR4) and the four diodes that make up the bridge rectifier on the power supply (CR6-9). now instead of dead displays i get this:

http://www.youtube.com/embed/4j0Atzy2qm4

checking the displays in the test menu shows no improvement. something is "working" because they change while scoring, but nothing usable. plugging/unplugging the individual displays didn't improve anything. all connectors are good and clean and snug.

noticed Z16 and Z17 (the 7448 decoders) on the MPU were screaming hot, made me wonder, though the game and sound proms were also hot and they still seemed to be functioning fine....

just found this regarding someone else's issue, but seems like it could also apply here:

"Since you said the problems show up same on players 1 and 2 and same on
players 3 and 4 - you need to look at digit strobes, not segment drivers.
Digit strobes are driven by Z18-Z21."

Z18-21 are 7408's

any feedback much appreciated!

pdman, already been through that document a bunch of times. if there's anything apropos to my situation that i didn't mention in the first post, i am missing it (as i said, i am new to this). was hoping maybe someone had seen a similar display problem and could comment from first hand experience. i've posted this on three different boards and that site is always the first reply posted....

plugging/unplugging the individual displays didn't change anything.

i do have a logic probe and the schematics, though i've never actually used one. if someone knows what the readings on Z16-Z21 are supposed to look like i could dive in there.

alternately, would it be possible for me to buy the 7448 and/or 7408 chips and piggy back them on top of the existing chips to see if it makes a difference (before i go through the trouble of desoldering the old ones etc)? a friend showed me this technique on a video arcade machine but i'm not sure if it is safe/effective in all applications....

the 69v fuse WAS blowing. i think it was due to the solder bridge i left after reflowing a connector pin. it is good now.

when i got the pin everything worked as it should. then one day the scores started to flicker and dim. i thought at the time it was due to the cold weather, but eventually they just went dark altogether. i made a lot of mistakes trying to troubleshoot this due to my lack of experience, but it is back to the point where everything works properly except the displays.

i repinned all the connectors going to the PS. i did not do the other connectors because they are still "factory snug". i am only the 3rd owner of this machine. after a year on location, it spent the next 30 with the guy i bought it from. it is really in excellent original condition and i'm trying to keep it that way. i know buying the pascal or ni-wumph would be the easy way to go about this but i also really want to learn what is wrong and how to correct it.

i do own the genie manual and gottlieb ss manual. i've read all the "big" system 1 sites several times and googled till my fingers are ready to fall off.

i've been plugging away at repinning the connectors. so far no changes.

does anyone have a chart of what the pins on known working ICs on the MPU should show on a logic probe? i actually have a spare boardset now i could cannibalize.

no one's ever recorded the logic probe readings on a functioning board? how about just U6 when all the scores are sitting at 0?

pretty please?

THANK YOU, guilford bob!

i will take a look today and report back. i hate the idea of having to replace the original MPU, but if the spider is bad at least i'd know i can stop fooling around with other possibilities.

update:

after avoiding this problem for months, i replaced Z16 and Z17 and displays are working properly again.