I have a very nice Sansui 5000A receiver that has an intermittent phono section 'machine gunning' issue. Very annoying. One will be listening to a record and suddenly a loud thud-thud-thud-thud-thud.... noise is heard. Switching the selector off of phono and back to phono several times clears it up temporarily. The controls have all been de-oxit treated. Any ideas?

I have the exact same problem with my 5000x. It was so bad I could see the cones on the woofers of my Advents going in and out. Took the receiver out of rotation. I'm anxious to hear a solution as well.

'Motorboating' ..?
Self-oscillation in the phono pre-amp most likely if you get no-where cleaning switches.
I would do a re-cap starting with the 470uF/25V cap' that goes from Transistor TR605/Collector to Ground. (Sorry, my schematic is so bad I don't see the position-no.) :thumbsdn:
But isn't this receiver so old that it should be re-capped in full, anyway?

rgds,

/tri-comp

That's called "Motorboating" It is sometimes caused by a poor, corroded ground connection. Look around the phono board for attachment screws and then loosen them and then tighten them down.
DH

I have a very nice Sansui 5000A receiver that has an intermittent phono section 'machine gunning' issue. Very annoying. One will be listening to a record and suddenly a loud thud-thud-thud-thud-thud.... noise is heard. Switching the selector off of phono and back to phono several times clears it up temporarily. The controls have all been de-oxit treated. Any ideas?