so, got the donor unit and it has a bad power supply as I expected. So first checked out its acquisition board and the only channel that passes self test was CH2. So what I've done and pull the attenuator from the donor first and tried it. No change on my CH2 also no change to CH1.
the CH3/4 attenuator SMB connector was busted on the donor unit so that attenuator is no good.
I have some things to do today but tonight or tomorrow I'll pull the entire CH2 hybrid and socket off the donor and first try the socket then if needed try the hybrid.
one thing I did notice after using the flir one is it looks like the CH2 DAC is running hotter than the rest but i don't think excessively. datasheet says -40c to 80c and it's well within that range at ~50c.
after I replace the socket and swap hybrids I may set CH3 and CH2 up with same signal in and settings and compare the DAC pins.
I'm reaching the point I think there are some other failures on the board hopefully with jelly bean parts