Quote:
Originally Posted by dsergeant
I would confirm. Intermittent field collapse on TX90s are ALWAYS dries on the output transistors.
|
Thanks for the advice.
The field collapse seems pretty solid now, despite how it was described to me. I resoldered the transistors (and much else) last time the set was on the bench. I've just pulled out the darlington TR105 and it's showing reverse conduction from base to collector (not a short but it shouldn't conduct at all) so I reckon it's had it. I don't see how an output stage fault could stop field drive being present on pin 2 of the TD4500 unless an output stage fault damaged the TDA4500. Unless some odd effect in the feedback loop can stop the field drive.
I think I'll order a TDA4500, TIP112H and TIP29E from Grandata which will only come to about £5 the lot. I'll also recheck the soldering in the output stage and change C172 and C171 since either could have dried out.