Kenwood KR 4070 Hum in one channel

[Fgx3prak]

Hi,

I have a problem with my Kenwood KR-4070 receiver. Tuner works fine but Phono input has a 60Hz loud hum in the left channel. I used a shorted plug to isolate the hum and the right channel is quiet. Hum varies with volume, if that helps. The same TT and phono cable work without any problem with a different receiver, so I can say the problem is in the phono stage in the receiver.

I have downloaded the service manual but I don't see a detailed schematic. I have cleaned all the contacts and don't see anything like a burned resistor or cap. Does anybody here have experience fixing this issue? I am thinking of soldiering the phono jacks and replace the ceramic caps. Good or bad idea?

Thanks for any pointers,
Praki

 

[sgrossklass]

That can't really be anything more than a bad connection somewhere at the input, a bad transistor or maybe a bad input coupling cap. You've got two channels to compare, time to poke around with a multimeter.

Checking continuity on the jack itself and its joints certainly isn't a bad idea. Sometimes these things break internally, then you're in for some real fun.

It's the electrolytic caps that you may want to replace, leaded ceramics don't fail all that often. Doesn't sound like that's your primary problem though.