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Kenwood KR-6600 relay shutting on and off repeatedly, and pops and crackling with volume at 0

once you get your dbt, post the status of your receiver.

I'd put it back together (I think you disconnected jumpers to the amp boards).

is the dbt bulb bright?

what are the voltages at the protection pins asked above?

let's understand where the problem is located (amp, pre, power supply, ...)
 
DBT is assembled, the relay now does engage upon power up, though I remember this being typical behavior after a long time not being exposed to power. Maybe that gives you some clue as to what it could be? After a while it does start acting up, and although it will play audio fine at first, there are occasional loud pops in one channel after 30 minutes of being powered on, which I assume is a transistor issue. It's around 16-17mv at 10 and 17-24mv at 19. All I was able to find locally was a 200w incandescent which I'm guessing is a bit high for this application, so it is not lighting up at all aside from very faintly for a few seconds upon start up.
 
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Oh boy...

Measure the voltage across an emitter resistor for each channel.

V=IR

Depending on the value of the emitter, you can calculate the current.

Your EE roommate can help
 
I checked with the service manual, yes. 6 and 13 read 21.5mV, while 23 and 16 read 4.2mV. I tried to get a reading on the emitter resistors but it was difficult to reach, I believe one was 2.8mv or 5.96mA while the other was 10mv or 21.28mA. Should I go ahead and adjust using VRe1/2 to get 6/13 and 23/16 up to 40mV?
 
Just hoping you can help me make sense of some of this stuff. Adjusted back to 40mV. Relay still toggling back and forth, what steps would you suggest I take next?
 
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what is the voltage at pins
Left channel: 10
Right channel: 19

if both are under 50mV, the protection relay should be ok. I'd recap power supply 'A'. this is the protection circuit. At least verify voltages are listed on the schematic
 

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They are both under 50mV, I ordered the caps for that board, should be here in a few days. I'll update you when I get them put in, thanks for your help so far!
 
Caps came in today, just put them in and powered it up. The relay disengaged for a second or two at around the 15 minute mark, then re-engaged and has been running without interruption for a good 10 minutes, and just now did the same disengage/re-engage. If that info helps at all.

I only replaced the electrolytics, should I replace the ceramics and film caps? I have them, just not sure if what I have is completely correct. They match up to the service manual spec-wise but the film (mylar) cap looks quite different.

On the plus side the popping seems to have gone away, I'm guessing the bias was the issue there.

What should my next steps be? I can go ahead and try to replace the remaining caps or order some new ones for another board if necessary.

One more thing, the receiver makes a sound like a very quiet cicada, not sure how to describe it, after 10 minutes or so of being powered up. I doubt that is relevant, but on the off-chance it is I thought I'd make note of it.
 
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what board did you recap? Power supply 'C'?

And you used a bi-polar cap for Cr3? This is part of the protection relay driver circuit.

maybe share a pic of the board.
 
Recapped power supply 'A', but just the electrolytics. Yes, I used a bipolar for Cr3, I’ll attach an image of that as well.IMG_1671.jpegIMG_1673.jpeg
 
Check the voltages coming off the regulators Qk1 and Qk5 (pins 2 and 5 coming off the power supply "A" board)
The protect circuit also depends on those voltages being balanced. The voltages are controlled by the zener diodes Dk1 and Dk3.
One common cause is intermittent Qk1.
 
Thank you for your response. I was unsure of where to put my multimeter probes, but with just using one probe on pins 2 and 5 they both seem to be balanced, one at ~-5mV and the other at 5mV. Qk1 is very hot, but I assume that is typical given the giant heat sink. Relay was still clicking on and off while I had it on to test. Anything else I can test?
 
benjaminlee said:
Thank you for your response. I was unsure of where to put my multimeter probes, but with just using one probe on pins 2 and 5 they both seem to be balanced, one at ~-5mV and the other at 5mV. Qk1 is very hot, but I assume that is typical given the giant heat sink. Relay was still clicking on and off while I had it on to test. Anything else I can test?
Click to expand...
:idea:Not sure what or how you are measuring. By balanced, I mean the pin 2 should be +23 and the pin 5 -23 volts. If one is significantly different than the other (but opposite polarity) then the relay will cut out. Are you measuring with respect to ground?
Qk1 is normal to be hot, but many years of heating may make it intermittent. Also, inspect the solder connections as these can be intermittent because of years of heat.
 
I'm not sure what or how I was measuring either. My multimeter was on the wrong setting, sorry about that. Yes they are balanced, I'm getting 23.5 on one and -23.5 on the other. Anything else I can test?
 
First guess is to replace Qk1 - they get intermittent, and are the most common problem. Just about any NPN TO-220 transistor will work - TIP41, Tip 31, MJ15028, Mj15030, KSD526 off the top of my head. Anything with current rating greater than 3 amps and power rating greater than 30 watts. If the transistor is the original C1419, definitely replace it.
If the problem continues, to isolate the problem further, you can try grounding the pin 8 on the "A" power supply board (the one with the regulator transistor NOT the relay). This will prevent amplifier problems from triggering the problem. If it continues, it should be one of the relay controlling transistors (Qk2,3, or 4) oe problem with the solder connections. (resoldering and cleaning the connections can't hurt any way...
 
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