I have this older Kenwood KM 205 amp that I fixed a few months ago. When I received it, it had blown quite a few resistors, transistors, and a capacitor or two. I finally got it operational but there is just one weird quirk that I can't seem to figure out. If I turn it on, after it has been off for an hour or so, the power indictator comes on but the fault or "antithump" relay doesn't click, so I get no sound. I can turn it on and off, hooked up to sources and speakers or not, and I get the same thing. But after leaving the unit on for a minimum of about 4 minutes, I can turn it off, then back on, and the relay clicks and it will operate just fine from then on out.
I have noticed that the idle current on one channel takes a very long time to increase to 18mV (which is what is recommended by the factory, and is what I have it adjusted to on both channels). Once that measured voltage is about 9mV or so, the amp can be turned off and then back on, and it will be operational.
So what gives? Is there a faulty resistor somewhere? Maybe a tempermental capacitor? I have looked at it a few times now, but can't find the faulty part. Any ideas?
Everybody has "projects" they feel obligated to bring back to life. Sometimes those projects just aren't going to be fully restored. This is probably a problem you could spend more than enough time on and too much money. If you are just hacking away at this with nothing more than a soldering iron and a DVOM, you are probably better off just leaving the unit on all the time, if this problem bothers you. Otherwise I would be looking first at the capacitors in and along the power supply rail which feeds this channel.