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Can i ask for some help.. I would like to bias my v7000 but can't figure it out from the scheme.

jogunast ha scritto: ↑

lun 23 nov 2020, 13:00

Can i ask for some help.. I would like to bias my v7000 but can't figure it out from the scheme.

You should measure 20 mV (+ 20% -10%) between A and B (on both channels) by adjusting the R89 and R91 trimmers.

Thank you

left one is now 20mV - it was 12mV before.. for some strange reason I cant get a measurement out of R119 and R121 on right channel. Always measures 0, when i turn off amp it jumps to 500mV and back to 0. Can't understand what am i doing wrong..

Could these corroded parts (09647 022.97 - ferrite beads?) cause a problem?
P.S I'm sorry I started a thread in wrong part of forum.

The trimmer Is good?

Trimmer is fine i think. Problem is that with multimeter i get 0-1.5mV when i measure A and B points when amp is on, and when i turn it off i get >300mV.

*R117 - R118 are both 0.59V and R119 - R121 are 0..
Amp still plays, but I don't think its safe to use it before I find out what's the problem.

I'm sorry but I don't have the solution. I would not use the amplifier until the correct bias is restored. If you have an oscilloscope you can check if the sine wave is symmetrical and possibly understand in which branch the fault occurred.
I'm only an hobbiest... Sorry...

Thank you anyway.. Im only hobbist too.
Cold solder joints, capacitor replacement and biasing is my limit. I will need a professional to take a look..

These are my measurements - green checks with manual within few percent, red is off.. all soldier joints look fine. Amplifier plays fine, with only traces of sizzle on the right channel.
Before I drop >60€ on repair would anyone have some suggestions?

Very strange... the amplifier working fine... Check the diodes D15-D16.

took them out, tested them. they also work.

It was BC637..

Thanks for the info... Good for the next time...

Yes.. Couldn't find bc637, ordered bc638 and bc639 - closest equivalent. Since the legs of bd204 and 203 were shortly cut it would be unsafe to return them after testing. They will be replaced with same nos philips transistors. I hope it wont change the sound for worse.