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Kenwood KR-9400 Humming Sound - HELP

Semanon said:
Everything @spicer said. Something got dislodged or moved or changed. Trying to do non-invasive steps first before digging into the circuitry. Some got changed and we need to figure out what.

After doing Spicer's steps, open up the unit, and post some inside pics. Then, with the amp on, start moving wire bundles with wooden dowel or chopstick to see if you can change the loudness of the hum.

After that, start gently pushing on components in the power supply. A solder joint may have cracked or become intermittent. Gently is the operative word. Don't want to create new problems.

Finally, look over the PCB with a magnifying glass and very good light. Look for bad solder joints. Annular cracks are hard to spot.
View attachment 2437571 View attachment 2437572
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Awesome, will do so when I get back home end of this week
 
spicer said:
What input was selected in the video...?... not terribly unusual for a low level hum to appear on an open phono input at high gain, sometimes they come with shorting plugs on high gain inputs.... the unit has a microphone input if I remember correctly with a control labeled 'sound injection', is that control completely turned down? If you put your ear close to the speaker you can hear it change with the volume control, right? It does sound like 120hz, not 60hz, which is big clue heavily suggesting power supply issues. Just wondering, are there any sources of electrical interference nearby... a light, timer, other electrical devices. You mentioned it was not there before using compressed air to blow dust out of the unit, is that correct? Just because, try reversing the plug in the outlet and see if it makes a difference.... measure the ground side, cold, of the mains at the plug to a known good ground for excessive voltage, it's ac so some will be present measured with a high impedance meter like a DVM...or try another outlet.. kind of a reach but it's worth investigating. Every now and then a curious problem with a unit appears on AK that I'd like to have on the bench, yours is one of them.
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sound injection was off and turned all the way down.
 
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