The problem described is almost certainly caused by an open circuit video delay line, Z222.
Not sure if that 3rd party video encoder "upgrade" uses the original delay line or not. If it does, then you'll have the same problem after replacing the video encoder.
I've scanned a page out of my service notes
here to help you easily check it using an Ohmmeter. Check both Z221 and Z222. Applies to A600 and A1200.
They can be repaired, which is fiddly but possible, I've done it many times. You need to work out exactly what section is open circuit, then remove Z222 (you need to simultaneously de-solder all 3 cans in the row using hot air), carefully un-crimp the can and remove the ferrite core. The break in the wire will be at one of the legs and should be fairly obvious.
Repair it by using a strand of tinned copper from a piece of IDC ribbon, coil it around and solder to the leg, thread it to the cavity where the inductor coil is. Heat the tinned copper wire that's hanging from the inductor and solder it to the new strand of wire you've just fitted. Insulate and stabilise with some solder resist paint or similar. Test continuity and reassemble.
Keep in mind it's a very delicate soldering job. If you somehow managed to damage PCB pads while replacing capacitors, then you might need to find someone with good soldering experience to help you.
