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Repairing my Stereo

March 23, 2014

I have a Pioneer SX-3600 stereo receiver that’s served me well for over 30 years.  Just recently, it began to misbehave.  The most annoying thing was a burble in the sound that seemed to be triggered by vibration from the speakers.  The receiver and both speakers sat on a metal shelving unit that could easily transmit vibrations.  I found I could push and release the speaker selector switch to stop the burble, although it started up again sometime later.  Many of the controls and switches had also become intermittent.  I had to jiggle them sometimes to get them to work properly.

It was time to put the receiver on the bench and fix some of these problems.  The first thing I did was to open it up to do a cleaning and visual inspection.  Nothing was obviously wrong.  When I ran it with speakers on the bench, the sound was excellent.  The burble was gone.  Nothing I could do would make it return.  The controls and switches were still intermittent, though.  At least I could fix them.  I did have a can of contact cleaner, but there was no place to spray it.  The slide switches and controls were all completely enclosed.  Before I could clean them, I needed to make an opening for the contact cleaner.  I did this by drilling a small hole in the insulating board, away from the contacts.  Then I sprayed in the cleaner.

When I reassembled the receiver and put it back on the shelving unit, I was quite pleased with the results.  It was much better.  The intermittents were all gone.  I used it like that for a while, but then the burble in the audio returned.  What could be doing that?  It was unlikely to be a switch or control now.  They were all working nicely.  I had to reproduce the problem on the bench.  I ran it on the bench for days, for weeks, until the burble finally returned.  I found a trace on the bottom of the circuit board that showed a reduced voltage whenever it had that burble in the audio.  This trace connected to the centre pin of a large 3-pin device mounted on the other side of the board.  It was probably a voltage regulator, but may have been a power transistor.  The pin itself showed a steady voltage even when the burble was present.  That was it: a bad solder connection.  It was probably caused by heat.  The board was a bit discoloured around that device.

The fix was easy.  First I scraped away the old solder with a small blade.  Then I resoldered the connection.  Once again, I put it back on the shelving unit.  The burble was gone!  It never returned.  At least my major annoyance was gone.  After some time, one of the switches became intermittent again.  That’s a minor problem.  One day I noticed a large backlash in the tuning control.  I only listen to two stations, so that’s also a minor annoyance.  I can fix that if I have to.  Certainly I’ll have to repace the receiver some day.  The new ones available now all have a digital tuner, but otherwise seem to be the same.  I’m going to wait a bit, perhaps until some new technology comes out.  Until then, I’m going to stick with the old Pioneer.

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