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In Reply to: Hum in Sansui 9900 posted by SamS on June 12, 2004 at 14:46:28:
Some of the folks here will need a bit more detail to help narrow down the problem(s):* It does it on all inputs, right?
- Does it still happen with all connections to the amp removed?
- Does it do it with no speakers and only headphones?
- Does it happen with other outlets in the house?* What was the last change you made to the entire system since you noticed the hum?
- What was it, exactly, and did you have any problems getting the change made?
- What component was the change made to?
- How long ago was it that this change was made?
- How long did it go before you noticed the hum?That should get us inmates started - hey, they call us inmates for a reason.....
Cheers,
Follow Ups:
The hum was there once it was powered up with no other connections at all. Can see it on the meter too. No change at all just happenned after years and years of use? I have all the schematics, voltmeter but no scope. I can solder. Sounds to me like lost ground or power supply. How to trouble shoot? It is a great tuner even compared to its replacement Magnum. Should I not fiddle with it and at some future date send it off for mods and a fix? I certainly don't want to ruin it. The mod people are firm that you don't screw it up or they won't touch it.
Ok, that helps. So, I'd begin to suspect you've got a power supply problem and would seek to eliminate that from consideration. Logic here is that the bigger electrolytic caps used in the p/s are subject to drying out - a common problem in 20+ year old amps - tubed or SS.Check to see if these are getting warm, which is a clear indication they're becoming resistors as the film becomes hard. If you know what the operating voltage across the terminals is then you can also test to see if its up to snuff, too.
Alternatively, you can temporarily wire another one into place to see if there's any change in the hum - cheap and dirty way but not as scientific.
This, of course, assumes that you've pretty much stripped the system down to its basic parts - amp and speaker - and the hum is still there.
Thanks I agree your logic is sound. I'll fiddle when I get the time.
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