V7000 bias

Problemi tecnici vari - Technical problem? Need help? Post here
Rispondi
jogunast
Messaggi: 51
Iscritto il: mar 11 feb 2020, 18:05

V7000 bias

Messaggio: # 13120Messaggio jogunast
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.

Avatar utente
Gianfranco
Messaggi: 1568
Iscritto il: ven 16 feb 2018, 15:10
Località: Realtà a bassa intensità

Re: V7000 bias

Messaggio: # 13121Messaggio Gianfranco
lun 23 nov 2020, 13:28

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.

Immagine
Gianfranco

jogunast
Messaggi: 51
Iscritto il: mar 11 feb 2020, 18:05

Re: V7000 bias

Messaggio: # 13122Messaggio jogunast
lun 23 nov 2020, 13:35

Thank you 🙂

jogunast
Messaggi: 51
Iscritto il: mar 11 feb 2020, 18:05

Re: V7000 bias

Messaggio: # 13123Messaggio jogunast
lun 23 nov 2020, 16:19

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..

jogunast
Messaggi: 51
Iscritto il: mar 11 feb 2020, 18:05

Re: V7000 bias

Messaggio: # 13124Messaggio jogunast
lun 23 nov 2020, 18:03

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.
Allegati
2.jpg

Avatar utente
Gianfranco
Messaggi: 1568
Iscritto il: ven 16 feb 2018, 15:10
Località: Realtà a bassa intensità

Re: V7000 bias

Messaggio: # 13125Messaggio Gianfranco
lun 23 nov 2020, 18:21

The trimmer Is good?
Gianfranco

jogunast
Messaggi: 51
Iscritto il: mar 11 feb 2020, 18:05

Re: V7000 bias

Messaggio: # 13126Messaggio jogunast
lun 23 nov 2020, 18:27

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.

Avatar utente
Gianfranco
Messaggi: 1568
Iscritto il: ven 16 feb 2018, 15:10
Località: Realtà a bassa intensità

Re: V7000 bias

Messaggio: # 13128Messaggio Gianfranco
lun 23 nov 2020, 22:59

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...
Gianfranco

jogunast
Messaggi: 51
Iscritto il: mar 11 feb 2020, 18:05

Re: V7000 bias

Messaggio: # 13129Messaggio jogunast
lun 23 nov 2020, 23:08

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..

jogunast
Messaggi: 51
Iscritto il: mar 11 feb 2020, 18:05

Re: V7000 bias

Messaggio: # 13131Messaggio jogunast
mar 24 nov 2020, 15:13

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?
Allegati
1.jpg

Avatar utente
Gianfranco
Messaggi: 1568
Iscritto il: ven 16 feb 2018, 15:10
Località: Realtà a bassa intensità

Re: V7000 bias

Messaggio: # 13132Messaggio Gianfranco
mar 24 nov 2020, 15:36

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

jogunast
Messaggi: 51
Iscritto il: mar 11 feb 2020, 18:05

Re: V7000 bias

Messaggio: # 13133Messaggio jogunast
mar 24 nov 2020, 17:47

took them out, tested them. they also work.

jogunast
Messaggi: 51
Iscritto il: mar 11 feb 2020, 18:05

Re: V7000 bias

Messaggio: # 13264Messaggio jogunast
gio 10 dic 2020, 13:46

It was BC637..

Avatar utente
Gianfranco
Messaggi: 1568
Iscritto il: ven 16 feb 2018, 15:10
Località: Realtà a bassa intensità

Re: V7000 bias

Messaggio: # 13265Messaggio Gianfranco
gio 10 dic 2020, 14:22

Thanks for the info... Good for the next time... ;)
Gianfranco

jogunast
Messaggi: 51
Iscritto il: mar 11 feb 2020, 18:05

Re: V7000 bias

Messaggio: # 13267Messaggio jogunast
gio 10 dic 2020, 20:01

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.

Rispondi