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Rod, Systems Engineer
Category: Consumer Electronics
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Experience:  FCC Commercial Licenses, BSCS, ASEET, 40+years Electronics & Communication Systems
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I recently purchased a vintage Kenwood KA-7100. It works fine

Resolved Question:

I recently purchased a vintage Kenwood KA-7100. It works fine except the right channel distorts and crackles. Why is this?
Submitted: 5 years ago.
Category: Consumer Electronics
Expert:  Rod replied 5 years ago.
Hi Tony,

Does it do this when changing the volume or channel balance (left - right). Meaning to you hear the crackling more or less in the right channel?

Thanks,
Rod
Customer: replied 5 years ago.
No. It distorts and crackles Consistantly from the right channel only, not just when the knobs are turned. It almost sounds like the speaker is blown, although I switched the speakers and still crackles from the right only. Negating the possibility that it's the speaker. I then rewired the speaker to the "speaker B" position and the problem continued. The left speaker sounds perfect.
Expert:  Louie replied 5 years ago.
Hi and welcome to JustAnswer,

The Kenwood KA-711 is a 1977 model. Based on the age of the amplifier, most likely cuplrits would be coupling capacitors specifically in the pre-amp/tone control circuits. Additionally, these year designs uses carbon type volume controls and tone controls which are prone to dead spots, crackling and noise due to age.

Corrective measure for the controls would of course be replacement. Temporary workaround would be to spray the wiper/inside with electonic contact cleaner. The capacitors on the other hand does not have a temporary remedy, they must be replaced. Diagnosis and determining which would require a scope for visual check of no input signal level at the input/output end of the coupling capacitor. Another method would be shotgun approach, replace all of the signal capacitors. This of course would require familiarity with electronic components & circuitry, use of a DVM and a soldering iron. It would be to your added advantage access to a service manual or at the very least a schematic diagram.

Hope this be of initial help/idea. Good luck and thank you for using JustAnswer.

Should the above address your concern, please take a moment to click on the green ACCEPT THE ANSWER button. Appreciate it in advance.
Customer: replied 5 years ago.
I have no electronic experience. Should I even bother trying to fix it myself?
Expert:  Rod replied 5 years ago.
Hi Tony,

You could have leaking coupling capacitors, or near failing (read noisy) power output transistors for the right channel. However, the first thing I try in these type of units is to clean the switches and potentiometers. I think, in your case it may just be the switches that need cleaning. This unit is easy to work on. You just need to remove the top and bottom cover to get to the switches. DeoxIT is the best solution for cleaning the switches which you can obtain here. I don't think Radio Shack carries this, but you can check. I recommend the small bottle (around $15). Use the brush that comes with the bottle and like painting, slide it along the edge of the bottle to remove excess. Then touch the brush to the switch areas and contacts and then move the switches back and forth. Do all of the switches - its good preventative measure.

I've had a lot of success in solving noise from older units with this. If you still have the problem, then the right channel electronics will need to be diagnosed. I could be a simple coupling capacitor, but you will need a schematic and electronic experience. The parts for this can still be obtained, and its a good unit to hang onto.

Thanks,
Rod
Expert:  Rod replied 5 years ago.
Hi Tony,

You do not really need any electronic experience to clean the switches. Just disconnect the power when you remove the covers. What the unit looks like on the inside is available here. Just be gentle with the q-tips, all you are really doing with them is absorbing any excess cleaning liquid. The liquid, and the action of moving the switches back and forth will do the cleaning.

Thanks,
Rod
Rod, Systems Engineer
Satisfied Customers: 4497
Experience: FCC Commercial Licenses, BSCS, ASEET, 40+years Electronics & Communication Systems
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