Sansui G9000 driver board

Hi All,

I'm trying to fix a Sansui G9000. One of the driver boards (F-2806) had some melted resistors. I replaced the melted resistors, all transistors, D1, all electrolytic caps.

I reinstalled the board. When I bring it up on my variac, as soon as I reach 20VAC mains voltage, the amp draw starts to oscillate, swinging between 0 and 2A. If I bring the voltage up further the oscillation gets proportionally wider. The other driver board does not have this effect and swapping which side they are installed on makes no difference.

What else should I try on this board? Does anyone know the specs of the zener diodes D3, and D3? The service manual is too blurry to make out a part number, but it is here: https://www.hifiengine.com/manual_library/sansui/g-9000.shtml

What happens if you hit it with straight 120vac?  Some SS amps do not like to be variac'ed.

But the driver board from the other channel works fine on the variac.

Sam

samgraysound said:

..... anyone know the specs of the zener diodes D3, and D3?...

Click to expand...

D02,03  stv-3h
http://audiokarma.org/forums/index.php?threads/replacing-the-stv-3h-and-4h-diodes.279530/
ZD01,02 EQB01-22
http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=EQB01-22

Have you checked output transistors?

moamps said:

D02,03  stv-3h
http://audiokarma.org/forums/index.php?threads/replacing-the-stv-3h-and-4h-diodes.279530/
ZD01,02 EQB01-22
http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=EQB01-22

Have you checked output transistors?

Click to expand...

Thanks. I have checked the output transistors.