Hi - got a -35 on the bench. U15 was buggered so replaced that and the board booted but after the 7th flash when it should go to a half LED the LED either locks on (like an 8th Flash) or Resets and then goes in to a reset loop for a few cycles then eventually locks on.

The Reset voltages U9 Pin40 always stays high 5.2v
VUA stays good throughout
Replaced all socketed chips but no change
Very minor acid damage along the bottom earth line but generally much much better than most I've seen.
IRQ line is good to U10 U11 and seems to stay good through the cycles

Where to start? Never has this before...

#2 4 years ago

AMS

barakandl

nvram.weebly.com

12y 132K 10,417

OP
Quoted from crazi:
Hi - got a -35 on the bench. U15 was buggered so replaced that and the board booted but after the 7th flash when it should go to a half LED the LED either locks on (like an 8th Flash) or Resets and then goes in to a reset loop for a few cycles then eventually locks on.
The Reset voltages U9 Pin40 always stays high 5.2v
VUA stays good throughout
Replaced all socketed chips but no change
Very minor acid damage along the bottom earth line but generally much much better than most I've seen.
IRQ line is good to U10 U11 and seems to stay good through the cycles
Where to start? Never has this before...

Check the display interrupt and zero cross frequency. 120Hz at U10 P18 and 320Hz-420Hz at U11 p40. A lot of DMMs have a frequency test setting. If the display or zero cross interrupt is to far out of time it can be the cause of 7 flashes then crashes.

#3 4 years ago

DAD

crazi

Pinside member

Coatbridge

15y 41,400 307 8 6

I'm getting 100hz (UK) and 300hz - so both looking ok.

#4 4 years ago

DAD

crazi

Pinside member

Coatbridge

15y 41,400 307 8 6

It has stopped resetting - it is a constant 8th Flash now and hangup/crash... replaced U10 socket but still the same

All the data/address lines on the Processor seem to be pulsing even after the crash. The vma/vua seems fine to.

Yet it's an immediate crash after the 7th Flash...Stumped...

#5 4 years ago

PIP

Quench

Pinside member

8y 114K 8,029

Post some clear high res pics of the board (front and back).
Which game ROMs are you using?

#6 4 years ago

DAD

crazi

Pinside member

Coatbridge

15y 41,400 307 8 6

Been at it all day today but got it fixed

Was getting the 7 flashes and then LED lock on...

So replaced U11 socket and then I had some weird stuff happening. The board would "skip" the 1st flash but then got 2nd and 3rd flash and stop... WEIRD! I never thought it could skip the 1st Flash and carry on!

So Pinned out U11 and it looked good. So I pinned it out again right up to it's next component and found an issue and when I found that issue I noticed another one next to it. The two through holes bottom left of U8 running to U6 Pin1 and U8 Pin21 where not making contact properly. So wasn't getting the 1st Flash (U6) and stopped at 3rd Flash U8...

Fixed the through holes and booted and stable.

So I think a mix of the through holes and U11 socket. Perhaps the heat when soldering on U11 opened up the bad connection on the through holes. So was getting 7 flashes but maybe "just" and then crashed which would make sense because basically poor connections.

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