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Kenwood KR-4600 Repair

Spenser

Spenser

Mostly Discrete
Subscriber
Hi. Starting on Kenwood KR-4600. I've cleaned the pots and switches twice front panel and rear (has two rods to geared switches on the back panel board). The problem persists.

Here it is. Right channel great. Left channel weak in power, lacking in mid- and bass-range. If I could describe, it's like the signal is going through a strainer and much of it is getting left behind. I would estimate the left channel is 5% the strength and robustness of the right channel.

EDIT: PLEASE SKIP FORWARD TO Post #14. Problems in the power amp (left channel). Also, mains are reading high in the power supply. THANKS.

Loudness push-button brings up the bass some. Thought maybe the issue was there. Drilled a tiny hole in the tail end of the switch case in order to be sure cleaner was getting in there. No change. Thought maybe the monitor switch. After working the monitor switch rapidly and repeatedly (also dousing with cleaner -- or attempting to -- it's one of the ones on the back panel), no change. Boy are those switches in the back a pain to get to. This whole unit is fairly tight quarters. Nice looking from the outside.

What do you think?

I don't have a service manual for this one yet. I only put it up on the bench to check the lamps before putting in an order with Messr. Wojnarowksi for a single lamp for a KR-5030 ... and, of course, had to see if the KR-4600 worked, and NOW THIS KR-4600 HAS SUCKED ME RIGHT IN! You know how it is.

Let's see I have a second-hand, generic signal generator and a scope which I have not yet put to use. Is this my opportunity to get my feet wet on tracing a signal? Probably there is more to do before going there.

Should probably in any event put in my order with Rick Stout for the service manual. There is not a service manual on HiFi Engine that I could see and I like to work from good paper.

Thanks man.
 
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I've never found a freebie manual for the 4600/5600. Just as well since most freebie manuals suck.

Before you get too carried away diagnosing clean all of the switches and pots. I don't like the idea of drilling holes to get cleaner in unless you've had one apart and know exactly what's in there that might be damaged. And even then...yikes!
 
Yes. Probably got a little carried away there on the push-button switch. I took care. Might even plug the teeny new hole in the tail end before closing up the work. Made sure no fragments got in to pollute the workings. ALL switches and pots done twice, some three or four times. Hard to get to a couple things. Would need to unstring I think to really get in there on the volume pot?
 
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Hey turboyam. Thanks. Yes ALL inputs. Also, mono switch no change. Tried headphones. Almost as if there is a bad connection somewhere. On that score, gently poked around components in power amp board, too. Visually inspected underside for any badness a person could see.

Note: I like the treatment of the component lead solder work on this Kenwood KR-4600. From the factory almost 100% straight out, therefore easy to desolder and snip with no fuss as opposed to bent or bent over hard, with just the right amount of tail left that a mini-grabber can hang onto. Nice.
 
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Common Smalls, you Primantis Bros lovin' fool, (quaddriver), I know you got an idea, now give it up, you!
 
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look up elektrotanya (sp?)

they have the scm in a very hi res scan, still faint, but very hi res
 
I found the site but am frightened by the Russians and the PDF reader the site is asking me to download ... but the $21 price of the manual might get me to overcome my trepidation. "Is it Safe" (from the movie Marathon Man).
 
no dont download, just click on the manual and scroll down,,,, there is a status msg that says 'preparing' then it says ready. norton has always told me its virus free
 
HORSEFEATHERS! Missed this earlier. I took a closer look. SOMEONE'S WORKED ON THIS RECEIVER.

Looks like C29 on the power amplifier board was replaced. Looks like neighboring R41 and R43 were taken out and put back in. (Note one of the soldering pads for C29 got wiped out in the process.)

The schematic I got from the Russians is so faint cannot say for sure BUTT -- if C29 is where I think it is -- it could be shunting the base of the upper left channel driver transistor AND the base of a transistor pair that feed back off the emitter of the output transistor, and then circle back into the base of the aforementioned driver transistor, if that makes sense.

IF the problem indeed IS in this vicinity, it might comport with how the problem sounds to the ear (guessing we have around 95% weakened signal strength, AND it-is-as-if only intermitent pieces of the waves are making it through).

Thanks.
 
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Before I start testing individual components, here are some readings and a picture of the power amp schematic for your consideration.

Power Supply
-Power supply mains should be 21V and are 26.5V. Almost 30% high is weird Edit: When I connect one lead of a multimeter to the chassis -- other probe free-- I'm getting a reading of 5.6V.

Power Amp
-Voltage at Pin 8 should be 30V and is 35.3V. Look for Pin 8 above Q9. Likewise Pin 7 should be -30V and is -35.3
-Left Channel emitters Q9 and Q13 should be 1.16V and are .01-.02V.
-Test point between R27 and R29 should be .5V and is .02V.
-Output resistors (Bias), R53 and R55 are swinging wildly between 18-33mV. Should be set at 40mV.
-Right Channel good. Bias is too high and unstable but not as wildly varying as the other side.

WHAT DO YOU MAKE OF THESE READINGS?

Kenwood KR-4600 Power Amplifier 03-05-18.jpg
 
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Hi,
recently I've worked on this one with the very same problem. I changed all electrolytics on the amp board and the problem persists. Voltages in my unit are also high. Weird behavior I encountered is, when left turned on for few hours, the problem seemed to disappear and both channels sounded very nice then. That leaded me to electrolytics, but the idea was probably wrong.
If you were able to take readable photo of the whole schema for me, I would be the happiest person. I'm servicing the unit for a friend and I want to get that thing working just fine. I hope we both will achieve that. It's tough job to work on this unit.
 
I don't have the camera or copying capabilities to do the job (readable photo of the whole thing). It's five times the size of the above segment. That large a piece, predict will lose sufficient resolution. I mean we can try it but that is my forecast. You can get a super quality reproduction on paper from Stereo Manuals for $21. He does computer file copies, too, I think for less. A bonus is the service manual also covers the KR-5600.
 
Oh, I see, no problem. I looked at those paper offers, but I'm afraid shipping to my country (Czech Republic) would rise the price too high. And I don't really believe this baby will land on my desk any again. Well good luck with it. I'll report if any progress will occur. I guess you're stuck at the point, or maybe you can mention some new info on the subject?

Many thanks.
 
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