Problem: S-video signal of the U64 not working anymore.
Lets start finding the problem
Probed the Chroma and Luma signal on the video port with my scope. Left: Chroma, looks good. Right: Luma, not looking good.
Lets probe it directly on the DAC
That is looking better, but nog good enought..
I did a probe on the capacitor, and it looks like the signal is draining to ground. But after replacing the capacitor it is stil not good. So it must be the DAC.
Lets start finding new DAC
I searched on several sites if I can find the Triple 10-BIT 180-MSPS Graphics and video DAC (THS8136) in the good package (TQFP-48).
Couldn’t find the part. So connected my friend Gideon Zweijtzer if he had a scrap board, and he had some! Yeah! He sended me a few board.
I salvaged the Video DAC from the scrap board..
And placed it on my board, and yes! S-video signal is working again!
Test on my Commodore 1701 looks good.