Sansui QRX-6001 blowing fuse and loud hum with no other output in one channel

[Reed]

Over the last several years I have purchased two QRX 6001s with the intent of restoring one and using the other as a parts unit, and possibly restoring the parts unit if the first unit didn't need any of the rare parts.

I got the first unit recapped but it still had issues so I shipped it off to be repaired. The unit shipped back and still had issues so I am now inspecting my "parts" unit to see if it is actually in better shape than the unit I recapped.

Surprisingly, the parts unit seems to function almost perfectly with the exception of blowing the fuse in the front right channel and having no music output but just a loud hum in the front right channel before the fuse blows.

Any thoughts as to the cause? This unit is all original (with the exception of the power cord which was cut off when I purchased it and the power transistors on the front left channel which have been replaced with modern standard looking transistors) and all functions seem to be working fine other than the one channel and some burnt out lightbulbs.

I am thinking either bad transformers on the front right channel or a problem on the amplifier board for the front. Any input would be greatly appreciated. Thanks in advance.

 

[par4ken]

Blown output transistor(s) in the right front output channel, you usually loose the driver transistors and circuit resistors as well. Looking at the same repair same as was done to the left channel.

 

[Reed]

Thanks. I swapped out the transistors for two known good ones but the problem remained. I swapped the rear board to the front board position and lost a few resistors on the board. I then took a close look at the other board and spotted a burnt resistor. I will be recapping both boards and replacing the transistors and blown resistors. Hopefully that will cure the problem. If not i will start looking into the power supply PCB.

 

[par4ken]

The driver transistors could be bad as well, and swapping good parts into the faulty unit could possibly damage the good parts, if any faulty parts remain. Check all resistors and transistors when recapping. When you get it working check the bias current if too high the amp will quickly blow again. Good Luck. Or you could just use the QRX-6001 as a preamp and decoder fed to another amplifier.

 

[Reed]

Thanks. I am working on sourcing replacement transistors for the two driver boards as well as the output transistors. I am going to go ahead and completely rehabilitate both driver boards while I am in there.

in the meantime, I need to figure out why my other 6001 (the unit i recapped and had a professional work on) has no right channel in phono mode, has no indicator lights functioning, and has an iffy left front and rear channels. Argh.