Condenser is the "old fashioned" name for capacitor, same thing
As for the clock source jumpers, the CSmkII requires these to be in the "internal" position, this is where the clock signal generated by the motherboard's crystal oscillator is used by the rest of the motherboard for timing purposes. Perhaps the CSmkII does not generate this itself for some reason, most of the other CPU boards with built in clock require the motherboard jumpers to be set to external clock.
It could be that there is something wrong with either the motherboard oscillator, frequency dividers, or delay line (U102).
If you have a counter, I think you should have 25MHz on both clock jumpers, from memory.
A lot of those oscillators were fitted into machine sockets, which can become loose and cause an intermittent connection on the oscillator module. Would be worth checking.
If you have an EC030 card (A3630?), you can try that, as they require motherboard clock.
Don't forget the CSmkII uses a few additional lines to the motherboard that the A3640 doesn't, so it can be possible where one card can work where the other one won't.
However, unless you can check the CSmkII on a known working machine, you're only speculating.
Perhaps you can send it to a friend somewhere else to test? Would only cost freight.
