25K7000 with multiple issues

[Peale]

did you get the black hole fixed on your chassis? If not, test Q8....if it is working then your problem is in IC1
Good luck.

Q8 tests good, but replaced anyway with a known good one. No change.

IC1 replaced with one from a donor chassis. No change.

However; I do note a difference in reading from one chassis to another, when reading Q8 in circuit. Methinks something is off down the line. Now, I just need to track it down.

 

[Peale]

I can get the blob to disappear when adjusting the VSIZE upward, but then it's too big. But, only just.

 

[modessitt]

Hmm. i think there is a transistor or diode near IC3 that handles the trigger pulse. Maybe check along that line...

 

[Buffett]

i have seen several chassis that R69 and or C28 were bad and needed to be replaced.

added them if they were not there or replaced the bad parts and it came back to life.

Peace
Buffett

 

[Peale]

i have seen several chassis that R69 and or C28 were bad and needed to be replaced.

added them if they were not there or replaced the bad parts and it came back to life.

Peace
Buffett

Somehow I missed this reply the first time around, but this thread:

http://forums.arcade-museum.com/showthread.php?t=234817&highlight=k7000+blob

Led me to the solution. The add-on board, on the left, as you face the back, was missing the 27pf ceramic cap. Replaced it, and was good to go.

That thread should be added to the K7000 sticky.

 

[paul400]

4) while going over the chassis for abnormalities, I note that the 4th wire on P202 has been cut out. I can't seem to find any technical docs on why removing that might be a good idea, so I'm just about to replace the assembly with one from a donor chassis. If I've traced the neckboard correctly, this may help with the blue that appears to be nearly completely on, all the time.



I was working on a 25in k7000 yesterday and noticed this wire was also cut. ever find out why?

 

[Peale]

Whatever the reason why, it was done at the factory. Some are like this, some are not. I put it back the way it came.