DK Jr PCB Sync Problem

troxel

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Donor 7 years: 2015-2021
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Got this in a lot of pcbs and game will not sync. I replaced the 2 pots and started to trace the sync signal back from the p7 connector. I loose it at Q12, and thought that was my problem and replaced it and get the same problem.

The signal comes from pin 25 on the ribbon cable to R92 (it does not go through K1 due to how it's jumpered). I have the signal on the base of the transistor and then I loose it. The collector and emitter are both high.

On a side note...for some reason all the ceramic capacitors have been cut off from row A1-R1. Would this affect the sync?

One photo shows the jumper and the other shows the missing ceramic caps.

Any suggestions would be greatly appreciated!
 

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Here's the signal going into the video board. Looks like a pretty short pulse, but wondering if this is correct or not.
 

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Figured it out. I inspected the board more after noticing the caps were missing and noticed there were 4 missing capacitors in the hysnc and vsync circuit. Replaced all 4 of those, and it brought the sync back.

Which begs the question... why would someone remove close to 50 ceramic caps varying in capacitance on this board? They weren't desolder, but simply snipped off.
 
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Figured it out. I inspected the board more after noticing the caps were missing and noticed there were 4 missing capacitors in the hysnc and vsync circuit. Replaced all 4 of those, and it brought the sync back.

Which begs the question... why would someone remove close to 50 ceramic caps varying in capacitance on this board? They weren't desolder, but simply snipped off.

Obama, thats why.
 
Figured it out. I inspected the board more after noticing the caps were missing and noticed there were 4 missing capacitors in the hysnc and vsync circuit. Replaced all 4 of those, and it brought the sync back.

Which begs the question... why would someone remove close to 50 ceramic caps varying in capacitance on this board? They weren't desolder, but simply snipped off.

Because that's the way, DaveZ rolls
 
Because that's the way, DaveZ rolls

The board did not come from DaveZ; however, the scope shown in the above post did come from DaveZ :). I am probably one of the few people that had a good transaction with him.
 
63 capacitors are missing from both boards. Looks like a boring project to replace them all.
 
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