Kenwood KA 4002A arching power switch?

[Daan*]

Looking for some advice for my little kenwood KA 4002. It has been totally restored around 2 years ago (recapped and risky small signal transistors replaced) but has had the same reocurring problem. Every now and then it will make a crackling noise through the speakers for around 10-15 seconds. This happens when i turn it on in about 1 out of 3 times. It never happens when playing or when turning off. I'm i right to suspect the power switch?

 

[rschweitzer]

Probably. If you can hear a little sizzle type noise at the power switch, volume control at minimum, then you diagnose is correct. That being the case, depending on the power switch itself, if it can be disassembled and cleaned, that would be good. If not seek a replacement.

To fix this problem for good, insert a triac. This is what I always do regardless if the switch is good or bad. There are several thread on this issue here on AK. There are others whom have inserted relays, but the triac method has worked well for me.

 

[Daan*]

Thanks, i will do some research on the triac

 

[claneg]

Another way to prevent arching on power switch, is to place an antiarching RC on its terminals. Even a C (x2 type) works. Kenwood and others were used to place a ceramic cap (2Kv capable) on the KA-x100 series and on.
Of course first thing to do, as rschweitzer pointed out, is to clean/substitute the switch.

 

[Daan*]

Finally got around to cleaning the switch. Maybe nice for future reference.
You can clean the switch without major dissambly by prying it open leaving the switch in place. You can then remove the small metal bars. Mine where really dirty (see photo) and one had some minor pitting.





Getting it back together was offcourse the hard part. There are two metal balls that have to aligne with the bars (see photo below). The bars just keep falling out when installing because of gravity In the end i secured the upside off the bar with a very small dap of nailpolish and got the switch back together. Has been working great for the last couple of weeks. Still have to look into a triac.

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