Ever since I've had them I had suspected the 2.5V supply to be at fault but had no oscilloscope nor variable PSU at hand, so they have been sitting in my drawer for a few months.
It was a 10 minute job:
- probe the 2.5V output and see it oscillating between 2.4 and 4.2V
- probe the PAL/AV output and see the scope could not get a lock even though it looked almost ok
- bypass the supply and feed 2.5V from a variable PSU
- probe and do a quick run to see everything is stable.
I wish I could do a burn test but my trusty variable PSU is a linear one, getting quite hot at this voltage drop.
Both DVRs have identical 2.5V supplies.
Oscilloscope locking onto the video signal, line 129.
Supply is getting quite toasty, it probably wouldn't be able to run for a full hour.
Image output on my temporary beamer setup.