SVT-2 Pro

[JC@]

The amp I have for repair does have this problem:
The standby / power / fault led is always red. It is supposed to go green as soon as the stanby is switched off, indicating that there is HV present. The led is ok, as sometimes it blinks green for a fraction of a second when I turn on or off the amp.

This svt-2 pro has been like this from the first day it was purchased, but now that it needs a bias adjust and it has a little hum (maybe because the incorret bias setting I'm guessing here), the owner want's the led issue solved.

I'm ready to look for a schem, but meanwhile maybe someone here has some experience with this amp and could make me some suggestions about this issue.

Thank you.

[drewl]

I had one with a defective bias monitoring/control circuit.
If I remember correctly replacing IC4 (TL072) and IC5 (NE5532) fixed the problem.

[JC@]

Great, I'll take a look there as soon as I manage to dismantle this thing..
Thank you

[drewl]

No problem.
You have the schematic?
If not I'll try and figure out how to post it....this forum is weird for me.

[Enzo]

I find it a lot easier just to email schemos, especially multipage things like this amp.

[JC@]

Yes I now have the drawing, and the EQ board comes out easily.
Best of all, I have some TL072 and 5532 on hand so I will check that.
thanks a lot

[Amp Kat]

Check your 10 ohm resistors on that main board also as that path to the TLO-72's are in that direction and a tube short is a likely candidate so check the 6550's too.

[JC@]

Fixed!
Thank you all.

[drewl]

So tell us.....was it the opamps in the bias control circuit?

[JC@]

So tell us.....was it the opamps in the bias control circuit?

Well I can't give *the answer*, sorry, because I didn't go step by step because of the hassle of testing every repairing step in a multiboard amp.
But here's what I did: first of all I changed both opamps because looking at the schem to me that seemed (sp?) quite a correct diagnosis, thank you about that.

Then I tested those strange looking phase inverter / part of the bias?
12au7's and they BOTH had a cathode to heater "soft" short. No wonder how those first generation chinese tubes won such a bad reputation

Firing the amp showed those lovely green leds on