Tonight I cleared the bench of dead 'scopes and detritus, dug out a 405 TV, spent some time working out why that didn't work only to find I'd nicked the ECC82
...
The Marconiphone VT161 displays stunning pictures, so I thought this would be a good test for the Hedghog.
Well it does work- sort of! It has issues!
The internal test card is quite juddery. It's like each field is starting a few lines vertically displaced from the next one.
Monitoring the video out, the internal greyscale pattern gives a nice stable stairstep waveform on the scope.
Switching to external input and feeding in a greyscale pattern from a 625 pattern generator, the 'steps' are twitching in amplitude.
Feeding in actual video from a DVD player and looking at it on the TV screen, it looks like there are sampling bits missing. The mid greys have a silvery look with no detail and there is noticeable background noise on the video.
I wonder if one of the data lines from the video decoder chip is missing?
My second HH is nearly finished, it just needs the IC's fitting. I can then compare the two and hopefully narrow down the fault. I've still only got one FPGA at the moment, but if the second HH displays the same fault, then it's probably the FPGA that's faulty.
By the way, there is no vertical judder when watching actual video, only when viewing the internal test card.
Cheers
Nick