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NBA jam "dead"

R3Demon

R3Demon

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Hello there,

Tell me if this is the wrong section.

I have a NBA jam pcb that doesn’t work. Symptoms are :
Only one led is on.
There is sync (but black screen).
In like 8 to 10 seconds, second led briefly lights on for a fraction or a second followed by a reboot.

Did anyone have these symptoms before?

I am starting to dive in this system without any experience with midway units.

Checked both program eproms, they are fine.
Battery is new
Full recap done
 
Last edited:
I have a bunch of Midway boards that only boot when flexed , or at least pressure applied to a certain place on the board

If you're getting the one red light and you've recapped , it could be something like that.

Tey applying pressure to different parts of the board with it on and see if you can get the BMMMP boot sound even for a moment
 
R3Demon said:
Hello there,

Tell me if this is the wrong section.

I have a NBA jam pcb that doesn’t work. Symptoms are :
Only one led is on.
There is sync (but black screen).
In like 8 to 10 seconds, second led briefly lights on for a fraction or a second followed by a reboot.

Did anyone have these symptoms before?

I am starting to dive in this system without any experience with midway units.

Checked both program eproms, they are fine.
Battery is new
Full recap done
Click to expand...
take a look by the JAMMA edge, there will be a large inductor coming off the +5V. the solder seems to break down here, you'll lose the +5V circuit that's supposed to power the chips.

also if you do dumb things like I have in the past using a Y-unit style sound board harness or one missing the key plug you can get it off a pin and blow that trace open like a fuse. lol

it's also been a number of years since I've done anything with these games. I yearn for a day where I can actually enjoy playing my games again someday.
 
I am testing without sound board anyway, on a T unit. Can’t find it but another nba jam i have starts fine without it.
What i found until now is that 5V is ok all over the board but not on those 4 caps next to each other near jamma connector. I am following that lead for now. Picture for reference attached, but with 4 caps instead of 2
 

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So I narrowed this down after few days away. Signal is pulled by the TMS34010 itsel or it's PLCC socket. Ordered few sockets from amazon, will be delivered in few hours and already got the original socket out (which is partially broken).
In fact I followed the reset signal, starting from PIN 3 on the TMS. Every auto reset, it's only at about 3.5V instead of 5.
Follwed the trace and found same result on many components ahead. And my oscillo decided to die on me so no easy way to find the real suspect.
Then i decided to just pull out the TMS, surprise, bad voltage disappeared on every other component.
I will update tomorrow!
 
Okay so after a new socket and anoter TMS tested, no luck, same problem continues. Old TMS installed on MK1 bootleg, works fine. I need to go deeper it seems.
 
Yeah that’s good. Now i identified TPC1020 as dead, swapped it and we have "better result". Both led are on and no more reset but still black screen
 
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