C Audio TR850 repair

[kevvywevvywoo]

Hello, I have a C-Audio TR850 old-timer on the bench for a quick tidy-up following a bodged repair by another. After resoldering a detached bus capacitor (the original complaint had been a snapping sparking noise!) and applying solder to the legs of one output transistor (it had been removed and replaced without solder by someone!), I'm now in a position to check the Quiescent Currents and Offsets. (the pots are chewed up as though someone's been having a merry old time with them!).

Does anyone know the correct procedure? Thanks in advance!

Kevin

[burbeck]

hi Kevin.
we have a c-audio expert here on the forum, do a search for Lee Basham, drop him an email, he is the man to help you.

[kevvywevvywoo]

Well would you believe it's still on the repair bench, there's a weird fault I can't bottom out without schematics. When switched into standby, various relays drop out as I assume they should, then after a couple of seconds or so start to creep back in with a gradually louder buzzing noise. I've changed various electrolytics and drive transistors but this part of the circuit is very complicated and dodges about all over the place.

[digitallake]

Originally Posted by kevvywevvywoo

Well would you believe it's still on the repair bench, there's a weird fault I can't bottom out without schematics. When switched into standby, various relays drop out as I assume they should, then after a couple of seconds or so start to creep back in with a gradually louder buzzing noise. I've changed various electrolytics and drive transistors but this part of the circuit is very complicated and dodges about all over the place.

A while ago! But I have schematics if you need them. Just refurbished a TR850 myself. Very good amps. The soft start circuit is a little over complex IMO, and prone to failure by the sound of it. I designed a simpler one in place of it, quite a lot of effort, but all working now.

[kevvywevvywoo]

Hi Jim, thanks for the offer. I have the diagrams, in a fashion, although the standby switching part of the circuit is different to the one I have here; there have been several circuit revisions in its lifetime and the rest seems the same, just the part that is giving the trouble!!

Yes..it's still here; the customer is no longer interested in getting it fixed but it would be nice to sort it as a spare amp for my own use.

[digitallake]

Haha... ok, yes my one stayed on the bench for several years before I got around to it

How interested are you in getting this going? I could maybe sketch the mods I did to mine on top of the C Audio schematics.... it did involve basically removing all of the soft start control circuitry and replacing it with a different, simpler circuit to drive the relays.