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-   -   Yamaha A 720 (http://www.diyaudio.com/forums/solid-state/133562-yamaha-720-a.html)

sylvester 21st November 2008 04:31 PM

Yamaha A 720
 
Hello everybody

My longtime friend has been sick lately and I'm hoping someone here can help me :sad:
When using the cd or tuner I often get static/cutouts mainly from the right channel.
Changing cables and speaker wires did not help.
I accidentally discovered that if I lightly touch or hold the corresponding button on the front I can recreate the problem.
After 20+ yrs. could he just need a good cleaning or is it something more serious?

Also his tuner buddy (T 720) never remembers his radio presets.
Is their an internal battery or something that I could replace?

Thanks in advance

Iain McNeill 21st November 2008 04:56 PM

I think you're on the right track on both counts.

An intermittent switch eh? Has it had a lot of use? If so the only solution may be to replace it.

Cleaning everything out won't hurt and may fix it:)

And on the tuner - yes, I'd expect to see a very old battery somewhere.

Good luck!

sylvester 22nd November 2008 12:55 AM

Yeah, He's been a workhorse. Easily over 10k hrs

Very little if any dust inside.
I used some compressed air and when I put it back together it still does it though not quite as much.
I also noticed that if I lower the loudness or volume knob (more so on loudness) the left channels will create alot of static/cutouts.
Right side does not seem affected now
:confused:
Think some electrical contact cleaner might help?

As for the turner I could find no battery :(

rabbitz 22nd November 2008 04:17 AM

The tuner probably has a super cap that provides the backup power. Look for a fat short cap 0.01-1F about 13dia x 7 high. Yeah, that's F and not uF.

Iain McNeill 22nd November 2008 05:37 AM

Like Rabbitz says, it'll be the same size as a battery. Can you post a picture? Is there a silkscreen? What's the reference designator? More info will get you better advice.

If you can consistently reproduce the problem by manipulating the pots then they must be #1 candidate for remedial action. I find that vigorous exercise (rotate the pot 0 - 10 - 0, 10 times quickly) scrapes most of the crud up to past full scale wiper action and provides temporary relief (just like me, you need to work out every day to keep those pots quiet)

Failing that, there's the cranolin and De-oxit specialty sprays but you need to get one that cleans *and* lubricates. It has to be a formulation for volume pots. WD-40 and the likes will just ruin everything. You don't want an oil, you want a solvent that doesn't leave more residue than it clears out.

edit, the PCB batteries can be very unusual shapes/sizes not aa/aaa etc. Look for some big blob with 2 (maybe 4 ) pins and usually a bright colored shrinkwrap plastic exterior.


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