Sansui QRX 7001 hum

[kpm0526]

Im a New member , I just bought a sansui qrx 7001 off the bay and it has a hum coming from the speakers . The hum is present when power is to the speakers on both front and rear channels and both A and B outputs. Its present in FM and Aux connect to a bluetooth streamer. With are only inputs ive tested so far. All controls are clear not scratchy. I checked speaker cables no issues. Polarity is correct. Any ideas what it could be. Im going to open it up and clean/deoxit but that is my extent of knowledge in repair. Thanks for any help.

 

[aldena007]

A hum on all four channels would indicate there are grounding issues in the pre-amp side being passed on to the power amp side of the unit. Check the ground points of the various circuit boards. Often there is a grounding pad/screws on one of the attachment points grounding the board to the chassis. When you setup your unit make sure you have the ground lug on the back of the unit wired to earth ground. If there is other units connected to the main amp the hum can be coming from them and being fed into your power amp. Tighten all screws on the various PCBs, ground the unit to the earth ground on you wall socket per instruction manual and disconnect any units like the phono, tape decks, tuners, decoders, etc.

If the hum is still there then you will need to dig into the unit a little more. You will now be looking for defective components. This will require some assistance with someone who is more knowledgeable at this point, Hum sometimes called "ground loops" are tough to track down.

 

[par4ken]

I would check the power supply capacitors first. Any signs of bulging or ooze coming out is a sure fire indication. If you need to replace them you will find that modern replacements are smaller than the originals. That opens up the possibility of increasing their value a bit for better than original filtering, performance.