Sansui 771 repair

Xeojij

New Member
Hello all nice man, I trouble you little with problem hope understand not with face loss. Sorry due my very poor english quality. I beg not for embargo on me.

I happy to buy SANSUI 771 receiver. But the ampli has some trouble. So sorry for parent hard work money :tears:

I do this:-

A)Clean the indoor with compression air to go away dust many years treasure
B)Clean the pot, switch, connector, check fuse if not corret amp. Every thing said ok
C)Change the negative and positive rail capacitor for the power supply board
D)Change 1000uf capa at volatge regulator
E)Using with variac to slow build voltage and power on

So here it is now:-

A)Left channel sound is getting. Right channel not
B)DC ofset voltage left is minus 157 right is minus 220. When the Relay goes cut

Where to look for trouble maker? If change all capacitor in driver board and power board he will get over being sick?
 
Is the DC offset steady, or does it rise?

If it is steady, try to adjust it down close to 0vdc.

If the dc offset is unstable, it could be the differential input pair transistors.

As for the right channel not working. Is this with all sources? FM, AUX, phono?

Could still be a dirty switch.

Rob
 
Thanks to understnd my english. I asked God send her bless for you.

DC ofset keeps going and then click does the relay i think which is protecting. Once more rotate trimmer again going to 250mv. Same cycle.

Yes heppening with all signal source right output slow.

Sorry does not have one signal tracer
 
diff input

so which is the differential input pair transistors?
 

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it is the pair with R13 and R15 as their emitter resistors. Note that the drawing seems to have incorrect transistor numbering...
 
It could also be a dried up capacitor. I just repaired an AU-717 with the same problem, and it was capacitor.

Rob
 
He is anymore not sick :banana:
All works . But the tuner is dead one. No sound no move of signal meter
one another thing. Phono is not so sweet and teh women's voice is like crack
I have change electro condensers new ELNA type.

Now tell me more so health is more better of him. Thank.
 
This is has start working in tuner osso :banana: yres no power had reached the tuner because t05 has dead then. so now new one put.

My more question is: their is Diode 10dc1 in main power supply. Is it improve if replace skotchy type diode?

So many thanks.
 
This is has start working in tuner osso :banana: yres no power had reached the tuner because t05 has dead then. so now new one put.

My more question is: their is Diode 10dc1 in main power supply. Is it improve if replace skotchy type diode?

So many thanks.

No, I would not advise this, use 1N5393 to replace 10D1.
 
Last edited:
No, I would not advise this, use 1N5393 to replace 10D1.
thank you so many . you good teaching simple line .
one things is still problem. phono is like shout high voice and pained to the eardrum. how it is done to like sweet? how make it to nice ladies voice? it is very importance.

same phono tt sweet in other ampli so it problem with this ampli. No?
 
Possibly, but might more likely be either interconnect leads (turntable to amplifier) or cartridge matching (with the input of the amplifier) OR a combination of both.
 
i am technics mk2 sl1200 where shure V15V xMR catridge is putted. it is got orginal wire to ampli but the RCA jack i put new monster brand. EQ board put ELNA capacitor and WIMA where blocking.

think what is trouble maker?
 
Hard to say what the cause is, but as you now show that you have re-capped the phono amplifier, this widens the search for the cause quite a lot. :dunno:
 
I good news reporting.

Last so meny days the ampli works fine. Everthing. Phono. CD & Tuner. All

So I thinking now go to doing the parts up quality. Oredi changeth elco capacitors well 80%

So now is it good to retirement tatantalum capacitors with MKP types? SOme EC type is bypolar. To replace that with FF type?

Is it well thinking?
 
I speak to early that my ampli is fine. It is one more time gone sick :tears:

Left ch centre volt i try to set to minimum. but something do pfftt do small spark. In the driver board. Negative line fuse burnt.

The pffft thing come with some smoke. i am worry if the out put transistor.

Now i do the replace fuse. measure cureent draw in left channel it is shoot 50ma just press power button. something is very big short. what ?

where i look? hwo testing if transisitor is pffft.


help to me :tears:
 
One another helpfull info is here:-

Right ch is not working also. But it is showing biase current steady 19ma. BUt when connect the speaker it also shoots more than the scale of amp meter.

Wht is it happening? :scratch2:

some pls help to me.:tears:
 
I am thinking output transistor is shorted down in left chanel.

I count the bias current with ampmeter in series with + rail supply. It is more than 100mA. That is the max my needle amp meter measures.

So it is shorted out put transistor in left channel?

Some pls help.
 
my 771 sansui ampli again is fine working. no sicked. the driver transistor left chellen changed Bd139 Bd140. Not more shorty the fuse

my one more problem is phono board. change the input and output capacitor with 1uf mkp.

Now the LP record surface noise is very high coming. And the voice is high with SIBIILIANT . I was thought it improve to sound if electro capacitor change for film.

So what is to do?
 
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