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Old 18th October 2011, 10:02 PM   #1
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Join Date: Nov 2004
Default Another diagnosis question?

I have a little Realistic STA-7 receiver that entertains my workshop adventures.

Yesterday it commenced to announcing the following complaint....

... a jarring, approx six cycles per second, "THUP THUP THUP THUP THUP THUP" via the connected speakers when powered on. Not severe enough to damage the speakers short term, but sufficient to wiggle the woofers and my ears uncomfortably. The condition persists despite any change of function via the controls... aux, phono, tuner, etc. Presently I'm using it connected to a cd changer via AUX outputs.

I'm not well versed in electronics beyond rudimentary function/repair. But I know I've heard this exact complaint from amplifiers in the past when they were in need of either loving attention, or a trip to the landfill.

Instinctively, as much as this will pain the purists here, I whacked the chassis with the palm of my hand and it cleared up!!!. It's working fine. But I'm pretty sure that this will return. My hunch is that a capacitor somewhere is on it's last legs and I was able to correct it temporarily with a mild physical shock. If that's correct, can anyone suggest a means to isolate the bad one? I'm comfortable replacing parts on a board, even smd's (tho I think amplifier this predates those).

Otherwise, any other suggestions as to what this portends? Like I said, I seem to recall this specific symptom from troubled audio gear in the past.
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Old 18th October 2011, 10:11 PM   #2
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Join Date: Apr 2008
Location: Carlisle, England
First port of call is a dry joint. Visual inspection theN solder any dodgy looKing joints.
If its of any age then I would also replace the electroltyics.
Murton-Pike Systems PCBCAD51 pcb design software.

Last edited by nigelwright7557; 18th October 2011 at 10:24 PM.
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