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Problem with Insignia stereo reciever

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henmill

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I bought an Insignia is-hc040918 stereo receiver (200W) from a pawn shop and it was in perfect working order for about 4 months. Then after Christmas break it began putting out a scratchy static-y sound ONLY from the left channel. It usually takes about 10 or 15 minutes before it starts to do this, so my obvious guess is when something heats up enough it starts to exhibit this behavior. It will do it at about a constant volume regardless of whether there is any sound coming from the speakers or how loud the sound is from the speakers, so long as the unit is turned on. I'm an Electrical Engineering student so I have a basic understanding of circuits and am experienced in soldering. I've taken it apart once to look for any clearly damaged components but everything inside looks perfect. Thanks for any help you can offer...I'm hoping it's just a blown component that can be replaced, again thanks anyone.
 
A possible cause might be the infiltration of humidity or moisture into the volume level control potentiometers.
I would suggest getting a spray can of electrical contact cleaner from your favorite electronics store, taking the case apart to where you can give any control pots or other switches a few pervasive sprays of the contact cleaner .... Allow to dry and reassemble.
Also, spray the RCA connectors of the audio outputs. ... Look for any switch or anything else that looks like it might move, and give it a spray or two.
This procedure often yields a performance enhancement, but is not too difficult to accomplish.
If the problem still persists after the spray cleaning effort, you should try to find a schematic of the unit, and proceed from there.

Electrical contact cleaner sometimes comes with a silicone compound. I would suggest that you initially try the version that does not have the silicone ..... I would not use the WD-40 product for this purpose.
 
Your audio switches and volume control are electronic so there's nothing to spray. ;) ;) Spraying the DSP chip isn't helpful. DO NOT spray the membrane switches behind the front panel. :eek:

More likely is a capacitor, failed and becoming leaky as the temperature rises. It would also be good to check all of the solder connections in the output area, as a dry joint can be noisy and temperature dependent. Tap on things with an insulated item (I use a chopstick) and observe what makes it better/worse. Wiggle the "preamp out" and "amp in" jumpers (items 10 and 11 shown in the manual, page 10).
 
... contact spray not appropriate for electronic controls or membrane switches... only mechanical controls and switches.

... Sometimes transient problems are due to the electrolytic type capacitors. You might try just leaving the unit powered up for a while ... a few hours .... days maybe. The idea is to 'normalize' the defective electrolytic that is causing the problem.

If you have the opportunity, you might post a picture of the circuit board.
 
Thanks for the info guys, I'll take it apart again and follow your suggestions and try to get a good picture of it as well. I was hoping it could just be a bad cap or something similar...I'd much rather replace a single or a couple components instead of the whole unit. If it is in fact a leaking capacitor, would there be any physical signs of damage? All I have access to is a cheap multimeter if I need to do any testing..would that be sufficient to test if a cap is blown? I imagine the right channel has the exact same components so if I can identify which components are for either channel I could take some voltage measurements on the functional side and compare. Thanks again
 
It seem unlikely that a newer unit such as yours .... a few years old ... would have a leaking electrolytic capacitor. However, it is certainly possible that one of the electrolytic capacitors on the problem channel side of the circuit board could be defective ... abnormal ... without any outward signs of a problem. You can eliminate the power supply as the problem .... only one channel .... not both.
Just as far as something to try .... when the unit is powered and still essentially 'cold', apply hot air from a heat gun or hair dryer to the problem channel section of the circuit board .... Maybe you can stimulate the problem capacitor into its malfunction mode and giving itself away.
Another possibility ... get a can of chill spray from the electronics supply store, and see if you can chill down individual electrolytic capacitors on the problem channel board section.
I've had mixed results with the hot air and chill spray methods ..... as mneary said, you just have to poke around sometimes.
 
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