Maddening A2000 Problem

[Computolio]

I recently resurrected a "fried" Amiga 2000, and it works fine except for one thing- A520 modulators refuse to work with it. It'll just give a rolling black screen. RGB with an RGB monitor will work, as does the onboard composite video.

Incidentally, a third-party A520 clone called the C-View will work slightly better when I plug it in- I'll get a very, very dark grey black-and-white picture from it.

It looks to be a problem with the CLOCK OUT line - all the other pins (including the power pins, which I checked first) seem to be OK. Thing is, I can't find any broken traces or pushed-in connector pins anywhere near any of the clock signals- they should be working just fine. This means that there's a dead resistor or something somewhere on the board. I don't quite understand what should be done to fix this. Has anyone had this problem before? It doesn't look like a very common one.