QRX-7001 Surround Modes in Trouble - Help Needed

[vinyleater]

I just acquired a second Sansui QRX-7001. It works fine in 2-channel mode, 2-channel plus back, and Hall Surround modes. That is, I get normal volumes from all four channels using an input to AUX from a CD player. However, when I switch to either Synthesized Surround, QS, or SQ modes, the volume to all 4 channels drops precipitously, making all these modes unusable. I do get some sound from all 4 channels, but it is very low even with the volume knob turned all the way up (which would be deafening in 2-channel mode).

I am wondering whether this could be due to an incorrect supply voltage to the decoder boards (i.e., above or below 25v.) or to some other problem that I could check. I know the 7001 does NOT have the pass through solder joints of the 8001 and 9001, which could cause this problem on those, if I remember correctly. I am not an electronic technician, but I do have some limited experience using a voltmeter and soldering irons.

Is this problem something that I could reasonably check for and correct myself or should I be sending this to a qualified repair tech? Since this is my second unit and acquired as a backup to a fully working one, I would prefer not to spend several hundred dollars having this serviced. Any guidance would be much appreciated. Thank you.

 

[AlamoQuad]

I just acquired a second Sansui QRX-7001. It works fine in 2-channel mode, 2-channel plus back, and Hall Surround modes. That is, I get normal volumes from all four channels using an input to AUX from a CD player. However, when I switch to either Synthesized Surround, QS, or SQ modes, the volume to all 4 channels drops precipitously, making all these modes unusable. I do get some sound from all 4 channels, but it is very low even with the volume knob turned all the way up (which would be deafening in 2-channel mode).

Hmmm... Interesting! Can't help with your questions, but I can certainly sympathize with your situation. My QRX-7001 has very similar problems, but slightly different. It works fine in 2-channel mode, 2-channel plus back, and in 4-channel discrete (R2R) inputs. However, when I switch to any synthesized surround mode, there is suddenly very audible hum/buzzing/squeaking introduced to the audio output. I am stumped!

Good luck. Hope you have made some progress in the time since your original post.