QRX 7001 protection mode and quad boards

[BeoProf]

My Sansui QRX 7001 stopped working today during a long listening session. There was a short buzz from the speakers and then all the channels went out. No smoke or smell or any visual effects. Now there is no relay click after turning it on and the receiver remains silent, but all the lights work. Looks like protection mode, I guess
I am quite worried now, as I really love this machine. From what I'm reading it could be many things starting from a bad relay to problems with the output stage. I have a great tech who can probably fix all the standard issues, but I am most worried about the quad boards and ICs.
Does anyone know if they could have been hurt in this event, or is the relay not engaging keeping them safe?
Thanks in advance!

 

[quadsearcher]

"Quad boards and ICs" implies line level processing, before the driver/output stages, so I would expect that stuff to be OK. That short buzz sound description sounds like what I've heard in other receivers when the outputs short and the description of the event sounds like that is what happened. A bad relay would not, I think, make a buzz sound through the speakers. By not engaging, the relay is keeping your speakers safe from DC. Protection Relay is sometimes described as Speaker Protection Relay. Turning it on like this should be avoided until it is repaired, as more components in the shorted amp section can be damaged by repeat power-ups. In case you are not already aware, make sure there are no speaker strands touching between + and -, even briefly, most common cause of outputs blowing.

 

[BeoProf]

Thanks, if the boards should be unaffected that is what I would like to hear - let's hope that is indeed the case. If it is a shorted output stage then it should be something manageable - the tech I know is really magnificent, and my only worry would be the quad boards. The short must be internal, the receiver was working for a few hours already when this happened and I haven't touched the wiring for months - I am very careful with speaker wires and used pin connectors with isolation to make sure I don't have loose strands sticking out.

About half an hour before the event I did hear some very light crackling, it was so faint that it sounded close to a record surface noise but I am certain it was not that - I thought for a second that it might be connections within the turntable, but it went away. I guess it came back with a vengeance

 

[Circular Vibes]

The crackling sound you heard "might" be and output transistor failing or a power supply issue. I experienced this with my 7001 and my JVC receiver. Do you have pets of the loose 4 legged kind? could there be chewing on a speaker wire where it isn't obvious? I had a cat that chewed my wires once, and no she didn't get electrocuted!

 

[BeoProf]

No pets, all the wiring runs through or behind furniture, I also checked later that the whole setup (4 speakers) worked with another 4-channel amp I have with no issues. I would say the most likely explanation is something internal so my money is on one of those Sankens in the output stage. If so that shouldn't be too difficult for a skilled tech to repair, I guess.

 

[Circular Vibes]

The parts are still available, thankfully. Good luck!