Pac Man garbage on screen

wishiwas

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Pac Man with garbage on the screen. No need to link to PM troubleshooting sites. Been there, done that, bought the shirt!
I worked on this board over a year ago and put it away after I broke some traces replacing the cpu socket. Just picked it back up and did the trace repairs and rang all the pins out and installed a new socket. I'm 90% sure that not it. I also replaced the cpu, vram and sync card.
What's odd is I get different garbage when I change the cpu or sync card etc but if you look at the pics you will see there is a pattern the way they display.
Based on another thread here, i tested the board with the notch oriented up, and the ground lead of multi meter on the bottom left leg, and the red lead of meter on the upper right leg, Im only getting 1.75 volts. Pin 11 shows 4.90 volts. Cap c51 is reading 0 volts, but i thought that was part of the sound circuit. C7 and 8 are 5.3 volts and c2 and 3 are 4.90 volts. Could the 0 volts @ c51 be the issue and if so, where to look. I'm using a switching dc power supply. Works good on other boards.
 

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I had this on a pac man recently and had me scratching my head as all I did was replace 6f. Turns out it was the 40 pin socket of the CPU at fault. Did you replace the socket or wiggle the chip as it's on to see if it changes?
 
Whoa, this is almost exactly what I'm seeing on my Ms Pac with the HSS multi kit right now. I was thinking 40pin socket or chip also since pushing on it would cause other things to happen, but that was a guess
 

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I tend to agree this issue may be related to the cpu / cpu socket. I mentioned where I probed based on another thread here and my voltage is low. What's causing that low voltage and 0 at C51.
 
AB6 is clearly stuck at to the 2114s.

Could just be a bad connection on the VRA, or 16V might not be getting to the VRA.
I assume you mean the 284 by VRA?
It appears the 284 gets it 16v from 2R pin 11 if I'm reading that right?
I changed the 161 @ 2R because I did not get any power reading from pin 11. (nice clean removal / install without broken traces / pads) and no change.
When I look at the pinout of a 161, pin 11 is labelled at QD so am I barking up the wrong tree? LOL.
As far as the 2114 ram goes, I swapped it all for 911s after reading your post. No change.
May I ask where you came to the conclusion AB6 is stuck on the ram and its not the cpu / traces around cpu? I don't mean that question to sound like I'm questioning your knowledge, I'm actually asking so I may learn :) That's the one problem with the typed word. You can't tell the inflection of person saying something.
B.T.W., thank you for your assistance.
 
May I ask where you came to the conclusion AB6 is stuck on the ram and its not the cpu / traces around cpu?
1739824044207.png

Garbage is duplicated every 2 columns of chars --> 16V --> AB6.

Doesn't mean the CPU isn't hosed too, but if AB6 isn't getting to the RAMs the code won't be able to do much.
 
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