dead TAF

elfyhead

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my TAF went kaput in the middle of a game a couple of weeks ago, and i'm finally getting a chance to get back to it. when i turn it on now, i just get a single fart out of the speakers, and nothing else, totally dead.

i've checked the fuses, and that's not the problem. so i'm about to dig into the "When things don't work" part of pinrepair, but i want to be sure of one thing.

there isn't a chance of actually damaging anything further by turning the machine on and leaving it on while i look at LEDs, check voltages, etc., is there? i just don't want to make the problem worse than it is now.
 
Well..

If you're worried about damaging stuff due to voltages, disconnect power to everything but the regulator board and then start checking stuff from there. That's what I'd do in that case.
 
OK, well, i poked at it tonight.

i turned it on, and first thing that happened was that it started to boot up like normal (D19 solid for a few seconds, then off and D20 flashing). that lasted about 5 seconds - about long enough to rotate the bookcase, then D20 went dark and D19 lit up, and everything went dark.

all the voltages looked good on the LEDs and test points on the power driver board.

so i unhooked all the cables but J210 from the CPU board, and powered it up, and same kind of thing. it turns on for a few seconds, then shuts down.

tested the voltages at the connector to J120 and they're all good - +5 on pins 4 & 5, +12 on pins 6 & 7.

so, looks like i've got a dead CPU board. i'm a sad panda. now i have to decide whether to spend the time debugging it myself (i haven't done a CPU board before, only driver boards), send it out for repair, or just replace it.

sigh...
 
is the f115 fuse blown? if so its likely your switch matrix on the mpu has crapped out, more specifically u20...
 
f115 never blew.

i reseated the ASIC tonight and no change. dead to the world. have to decide now how deep to go with the debug...
 
i followed the old pinrepair guide, and checked pins 3 & 37 of U4 (reset and IRQ pins).

both are supposed to be at 4.5V, but both read about 3.6V. would this be low enough to cause it not to boot?

the guide says to suspect U10, so i was going to check some voltages on U10, but in my WPC schematics manual i can't, for the life of me, find U10, so don't know which pins to test.
 
looking at the schematics, i'm suspicious of C31. it could be C32 or C33, but C31 is the electrolytic, so probably the culprit. i'll be testing voltages tonight...
 
voltage at the + of C31 is 5.08, so that's not the problem. sigh. found U10, it's the reset generator IC (34064) which look like a plain old transistor - i wasn't looking for that either on the schematic or the board, since i was thinking the U's are usually bigger ICs.

pin 2 of U10 measures 5.07V, and pin 3 is grounded, as it should be. pin 1 reads 0V - is that what it's supposed to read?
 
just to close the loop on this.

i got frustrated with the pace of my own repair and sent it off to coin-op cauldron.

it turned out to be the microprocessor itself (U4).

now, while that's a $5 part (or so), it'd have taken me forever probably to narrow it down to that, so i'm happy with my decision to send it off for repair. and happy with clive's communication, work, shipping, etc. the time and frustration it saved me is easily worth the $90 it cost. and i got the latest game ROM as well :).
 
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