Wanted: Schematic for vintage CJ SA Amp

[ducz]

Hello,

I have a vintage CJ Sonographe SA400 power amp, and am looking for a schematic to help me adjust the bias, the left heat sink is warmer than the right side.

If you have even a schematic for SA250? will help

Many thanks

 

[huggygood]

 

[ducz]

Thank you huggygood, exactly the same unit. It have 2 trimpots per channel, suspecting they are for adjusting the bias voltage but without the schematic/service manual, i have no clue where to begins

 

[rayma]

The amp looks simple enough to easily reverse engineer the schematic. Surely someone has done that.

 

[huggygood]

That was the goal of my photo, a fairly simple amp in appearance
You need at least two “good” multimeters.
What we're missing are the original values and knowing which channel still has the right bias value (and if that's really the case) and knowing why one channel is hotter than the other and that's maybe that is the right question.
By the looks of it, these must be Bourns potentiometers which are of good quality, they seem to have been touched, does the amp seem original, intact ?
Have you tried sending an email to CJ ?

 

[win33]

CJ Sonographe SA-250 schematic

 

[ducz]

Awesome! Thank you so much win33

Greatly appreciated!

 

[rayma]

So what DC voltages do you measure across the 0.47R emitter resistors?

 

[ducz]

both channels are ~73v. will looks into more details on the weekend

 

[rayma]

Is that 73mV?

 

[ducz]

Hi rayma, its 0 across it. Also add its only heat up when source applied.

 

[DCE1198]

Looking at the schematic, there are pots adjusting the balance of the input pair of transistors, so they will set the DC offset. They should be the two pots towards the center of the amplifier.

Dan

 

[rayma]

Do all the 0.47R resistors have 0VDC across them?
If so, check the bias circuit. The bias adjust transistor may be shorted, or the pot open.