@crustytv
May be other sets but doesn’t the RBM 823 chassis use the burst to ring the Xtal so the oscillator only runs with a burst.
Must admit to forgetting most of my PAL colour theory so again I may have a false memory, I.e. wrong on this point.
Frank
That gave me a crazy idea, Frank! I thought, what if I take the burst signal from the burst amplifier, and feed it back to the oscillator stage? So Ive connected a cap straight from the output of the burst amp (pin 14 on the TA7169P chip) to one side of the crystal, the result was the picture turned some very odd colours! A bit of fiddling with the oscillator coil got the colours almost correct, and further fiddling with other coils has resulted in a passable colour picture! There's quite a bit of patterning on the picture, but at least I have locked colour once again. Maybe I'll try a new chip, my thoughts are the oscillator section of it has died for some reason, the chip does seem to be quite warm, but all the voltages check out OK, maybe static killed it? it is very close to the CRT when it's all assembled.
Regards,
Lloyd.
Ok, there are some issues with the colour still, but they are to be expected I suppose! It has some problem deciding whether something is green or blue! On the test cards from the DVD player all the colours look correct, but on live TV from Freeview or from the Sumvision media box thing quite often blue comes out as green, red seems unaffected. I'm not going to investigate further now, I've shoved the back on! Damn thing can get out the way for a bit so I can do something else, and I'll keep an eye out for either another complete set, or just the chip that I suspect is faulty, a complete set would be better, as it'll probably work, and then I can test the chip from this set in it!
Regards,
Lloyd
Some photo’s,
Unlocked colour, using function generator to feed in 4.433Mhz
both sides of decoder showing my bodge!
the picture resulting from said bodge!
Regards
Lloyd
I recall certain models of Sharp VHS recorders that developed faults on particular chips, but the chips weren't cheap, or were hard to source, and a good few enterprising engineers worked out just what had failed within the chip, then set about building an external "bridge"? circuit to replicate that specific function. I even copied one or two of those mods on machines that came my way - Sort of reverse engineering the fix.
