02-05-2018, 01:19 PM
(25-04-2018, 01:13 PM)Mark Hennessy Wrote: Oh, and people usually recommend checking/changing the 3k3 resistors that drop the supply to the op-amp. I don't think I've come across these failing, but if one does go O/C, that tends to be "exciting"!
(25-04-2018, 02:18 PM)Crackle Wrote: Looks like you were spot on Mark, are these caps related to Callins by any chance.
They have a dry beige deposit on the surface, is that caused by leakage of the electrolyte though the resin case.
There is a 100uf 3v tantalum cap, do you think that would need changing?
I have not tested to see if the hum has gone because I need to order some decent quality capacitors to do justice to the Quad amp, rather than use my cheap ones.
Mike
I've had a 3.3k resistor go open. It even kills the crowbar circuit. The last thing to go after all the silicon is of course the fuses. In an odd Quad mistake the 3k3 resistors (that feed the input op-amp zeners) dissipate more than the resistor power rating, and they are mounted tight to the board. Replace them with at least 0.5W and preferably 1W ROX (it still fits the hole spacing) spaced off the board a couple of mm for air circulation.
The electrolytic caps in mine were Roderstein, and were well cooked with the cases discoloured and cracking. The caps in close proximity to the power resistors should be mounted on the rear of the board when you replace them.
Craig
