M2470LU

[mikey122]

Hello. When i got this nice boombox, it created high pitch sound and nothing could be heard. Then, i cleaned all pots, opened and restored every switch including rec/play switch, tested ESR and replaced two e-caps that were out of specs: 0.22uF 10V. Only that capacitors were bad. After that, only when mic is turned on it creates high pitch sound as can be heard on video. Note that this is happening on regular playback mode (and not recording mode) where IMHO mic should be off and there is no good use for mic to be turned on when not recording. This high-pitch sound can be heard on playback mode of cassette and radio (when mic is off, there is very good radio reception). Also, it can be heard on record mode.

Two questions: is it possible that mic can be turned on even if it is NOT on recording mode?
What could be the cause for these harmonics or high pitch sound? I made youtube video so you can see the problem. Thank you for help.
Also, schematics would be helpful if anyone has them.

Video of problem

Arrows on photo are pointed at mic input.

 

[BoomboxLover48]

First simple thing to do is to clean that long record switch.
Squirt Deoxit FaderF5 from both sides and move it back and forth a minimum of 30 times.
Squirt Deoxit FaderF5 is a contact cleaner and lubricant.
Wait for around 30 minutes and then check to see if it makes that high pitched noise.

 

[Fatdog]

Yep, follow BoomboxLover48's advice. From the symptoms you described, it could very well be the record bar.

 

[mikey122]

Thank you for answer. However, i tried that first. I disassembled all switches including rec/play and cleaned them with Deoxit D5. They were dirty but it did not made a change, high-pitch sound still can be heard. I uploaded another video so you can hear this interesting change in pitch. Do you have any other advice what to check? As i said, capacitors measured good ESR but they still might be bad? Any help is highly appreciated. Thank you