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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 17th Jul 2017, 10:53 am   #1
kevinaston1
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Join Date: Aug 2014
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Default Yamaha repairs

A pair of interesting Yamaha repairs, not particularly vintage, but interesting.



Firstly, a Yamaha MCX-1000 Musicast Digital Audio Server arrived on my bench faulty; it would not read CDís

Although it is an immensely complicated system; stupidly, I presumed it would be a nice easy one, a new CD drive and away we go. New CD drive fitted, now reads CDís but horrendous audio distortion. Playing a test tone CD, the audio was being chopped up at 100Hz.

I finally traced the offending signal to the PMUTE line, which was chopping up the audio signals at 100Hz. This signal comes from the power supply board, which is buried under every other board in the unit Ė and there is a lot of electronics in there.

When I finally extracted the power supply board, I found R420 open circuit, D420 short circuit, C433 and C441 open circuit. Replacing these and rebuilding the unit, it gave the unusual superb Yamaha audio performance.





Secondly, a dead Yamaha RX-V381; someone had decided that it needed a drink of Cola during a party. It arrived on my bench stuck in protect mode, and with a series lamp in the mains, if I brought it out of protect, it was drawing A LOT of current.

I had a quick check around the output stage, and every device seemed to be short circuit. After giving the customer the bad news, I was told to go ahead with the repair.

Removing all the electronics, I first of all cleaned the nasty sticky goo out the cabinet. That done, I set to work cleaning the said goo off of the amplifier board with cleaning solvent. After a thorough scrubbing and cleaning, all the shorts had gone. With the rest of the electronics cleaned up, I reassembled the electronics, and the amplifier happily came out of protect.

It passed all of its self tests, apart from the FM tuner module, which would not recover, even after a second cleaning. A new module gave the unit a clean bill of health.

Full marks to the Yamaha designers. Their comprehensive protection circuits worked a treat and prevented any damage to the unit.


Kevin
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Old 19th Jul 2017, 5:39 am   #2
Diabolical Artificer
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Default Re: Yamaha repairs

Nice work. I'm a bit of a fan of Yamaha kit, which on the whole is well built and designed. I'm talking about their older stuff, though it looks like they still design good stuff. If only Honda made electronics.

Andy.
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