Apple IIgs RGB monitor sync issues

edowen55

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Donor 2013, 2015
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I recently picked up a nice Apple RGB monitor to use on my test bench. I wired it all up, tossed on a TMNT pcb, fired it up and it looked great. Turned it off, thought that I wanted to take some photos of the TMNT pcb working so I could sell it, tried to turned the rig back on and it wouldn't sync.

I checked all the connections, tried a new board but it still wouldn't sync. Tested it a dozen times and then it worked fine again. Turned it on/off twice and now it won't sync again.

It's either perfect or horrible, no middle ground.

Any ideas?
 
I think I may have figured out the issue. Replaced the power supply and everything seems to be working now. Still need to test on a few more boards to confirm 100%.
 
I've always had really good luck with the Apple RGB monitor and negative composite sync. +composite sync not so much, and occasionally I'll hook up a board that is using higher voltage levels for the r,g,b signals. In that case the display will be washed out, I guess the chassis in those monitors was particular about a particular voltage range since they were just made to be used with Apple products.
 
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