John Moote
New member
I am refurbing a Sansui QRX-6500. The quad sections do not work well so I am in the process of recapping boards F-2047 and F-2048 and replacing transistors. I got the schematics and parts list for the Variomatrix boards from the QRX-5500 service manual which uses the same boards.
Just to be sure, I checked the actual components on the PCB's. A few minor changes to some capacitors but here is the quandary. The schematic identifies TR05 and TR08 as pnp's (2SA726) but the PCB has npn's (2SC871 which was a replacement used throughout this board for the SC1222). And it all looks factory original.
Here's the schematic, the two transistors in question are circled in red:
It looks like the npn's will work but it looks like the intent of the circuit is to phase invert two of the channels compared to the other two.
Maybe they ran out of the pnp's and they just stuck in the npn's? The capacitor replacements look like that is what happened. The only two 2.2uF replaced with 3.3uf, the only other two small electrolytics on this board. It seems like this would be an odd tweak, such a small change to a coupling cap.
The npn's probably work fine except for the phase inversion which would hardly be noticeable. Does anybody have this F-2048 board that they could check? Or does anybody know how this circuit is supposed to work?
Here's the board with the transistors in question circled:
Thanks for any assistance! An unusual find...
Just to be sure, I checked the actual components on the PCB's. A few minor changes to some capacitors but here is the quandary. The schematic identifies TR05 and TR08 as pnp's (2SA726) but the PCB has npn's (2SC871 which was a replacement used throughout this board for the SC1222). And it all looks factory original.
Here's the schematic, the two transistors in question are circled in red:
It looks like the npn's will work but it looks like the intent of the circuit is to phase invert two of the channels compared to the other two.
Maybe they ran out of the pnp's and they just stuck in the npn's? The capacitor replacements look like that is what happened. The only two 2.2uF replaced with 3.3uf, the only other two small electrolytics on this board. It seems like this would be an odd tweak, such a small change to a coupling cap.
The npn's probably work fine except for the phase inversion which would hardly be noticeable. Does anybody have this F-2048 board that they could check? Or does anybody know how this circuit is supposed to work?
Here's the board with the transistors in question circled:
Thanks for any assistance! An unusual find...