Kenwood KR-5600 relay/recap project; open relay needs help

tusntuk2

tusntuk2

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What's the best way to check the output relay in a Kenny KR-5600?
This thread is actually about two KR-5600's, one being my trusted old friend that's been working 20 years in original condition, and a second 5600 with an open relay I need to fix, then recap. It is also original, but hints at a frustrated solder monkey poking around...I've already found discrepencies in voltages between schematics and PCB layouts, and also to the "good" machine. Problem is, they don't make sense, so I need help! Eventually I'd like to create and provide a BOM for this receiver, it's a worthwhile solid performer. Figured I'd recap/upgrade my receiver with the new education, my fourth recap project. Thanks AK!
 
Probably do a resistance check across the coil, should be 600+ ohms. The odds of the relay coil going open are remote - if the relay won't close there's likely another reason. Most likely probably a shorted output transistor, next bet would be a problem in the protection circuit. A unit that's been messed with - who knows?
 
You know, I apologize. When I reread my note it sounded kind of mean, almost like a racial slur. I've considered myself a solder monkey for years, but it hit harder when I saw it in print. So I apologize for offending anyone, that's not the intent. I enjoy and need this forum to keep enjoying this wonderful hobby we share. Thanks for understanding my newness in here, I have much to learn.
That said, when I was faced with the relay that would not close I tried checking voltages discussed in other threads about relays, DC offset and bias, power supply regulation, etc. I also have a second working 5600 to check side by side. The confusion I have is that voltages on the "bad" amp seem better than the readings on the "good" amp! For example, "bad" bias is 38mv and 54mv after warmup, while my "good" working amp reads 41 and 56mv. "Good" DC offset is 11mv and 50mv, while the "bad" offset is -4mv and -2mv. Reading around the power supply regulator, the PCB says +/-14v for pins 3, 4, and 13.5v on 5. The "bad" amp shows+/- 19.91v on 3,4 pins, and the "good" amp measures -19.95v on 3, but +36.8v on 4! Digging in the schematic suggests a more correct voltage of about +/-18v. Both amps match 14v on pin 5, off the regulator transistor. +/- B voltage seems correct everywhere, measured at 39v for a 38.5 spec. I have not yet pulled the amp apart to reach all of the contacts on the relay. These are harder to identify on the schematic and on the actual board, and no values are given. What should I be reading? I did not remove the output transistors for testing after the DC offset came up so good - should I pursue that yet? Maybe I could just treat the relay like the Russian cosmonaut did - whack it with a hammer? And since I figure on recapping it anyway, I could recap the power supply board and see if that's all it needs. I wanted to find a problem first if I could before using the shotgun approach. Hope some of this makes sense, I'm still new at trying to describe what it is actually happening.
 
I didn't notice anything mean at all??

On the "bad" one - where are you taking the DC measurement? Since the relay isn't closing, you can't read it at the speaker terminals. Apologies if you knew that. Hopefully the s/m has info on where to read it on the amp board. I've never worked on a 5600.
 
I took a reading at the "0v" point where the emitter resistors meet before the relay. Seemed logical, but maybe not correct?
 
That looks right to this non-expert.

Qm26 looks to be the relay driver - what voltage do you get at the collector?

(...hoping someone smarter than me picks this up and runs with it...)
 
Qm26 reads 8.45v at the collector, if I read the PCB right. That would be one side of the relay, away from the speaker contacts. Reading across the diode to the corresponding side of these two contacts reads similar, at 8.38v. (Relay still open) Of course, if I try to measure the "good" amp the relay closes and gives readings of 200mv and 25.1v, which I would expect to energize the relay. There are no voltages given on the schematic for the relay, darn! Looking through other AK threads, KSC2383 is recommended for a replacement for the 1213, unfortunately I don't have one of those on hand, just common 992 and 1845's.
 
The 8.38 volts on the relay coil is way too low. With the relay not energized, you should see about 38 (B+) volts on both sides of the coil. So check RM70 (390 ohms) resistance with no power, and voltages on both sides with power. It also looks like QM26 is not turning on. The base should be at about 0.7 volts - if it is then transistor is probably bad. If it's lower, then you have to go backwards and check Qm25. It should have near zero on the base, and emitter is connected to ground. It should be 19 on the collector (voltage in the schematic).
 
tusntuk2 said:
Reading around the power supply regulator, the PCB says +/-14v for pins 3, 4, and 13.5v on 5. The "bad" amp shows+/- 19.91v on 3,4 pins, and the "good" amp measures -19.95v on 3, but +36.8v on 4
Click to expand...
The voltage on pin 4 is set by resistors RK2 and RK4. 38 volts means RK2 (470 ohms) is probably open. Other possibilities are open solder connection or open trace. However, these voltages do not affect DC offset or relay operation, but could shorten life of other components.
 
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Many thanks, gentlemen! Petehall, I'm a fellow brandy coffee man from up 'Nort, ya know? Now enjoying southern hospitality. On Qm26, B= .578v after some warm up. C= 8.0v, and E= 2.5mv. Qm25 shows B= 10mv, C= 13.4v, and E= 2.6mv. Thanks. too, to Steve for joining the thread!. Measuring the 1W Rm70 I get 39.1v on the B+ side, and the 8.0v on the other, as noted before. The resistor measures 400 ohms (.400k) on the meter. Hmmmmmmm. Guess I need to dig a little deeper in the well. (Jim)
 
try jumping qm26 emitter to collector briefly and see if relay clicks . i dont think it will but best be sure .
if no click remove one end of dm8 and see if relay clicks in then .
there is barely enough voltage on qm26 base to turn it on .
cm38 might have a problem and its going short . maybe change it first and see if relay clicks then .
 
If the 390 ohm resistor is dropping 30 volts, the current is going somewhere. Is the resistor hot? (it should be at that voltage). You may be correct in thinking the relay is bad. Thoughts- is diode across coils in correct, and not shorted. Should be reversed and not conducting under normal operation (it is a "flyback" diode which shunts voltage when relay is turned off). You can run the circuit for testing without the diode. Also, measure relay coil resistance. Somebody said it should be around 600 ohms which sounds correct to me. Something is definitely odd here!
 
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Wow, you guys are good! Lifted one end of the Dm8 diode and it looked odd, all right. Nestled down between a larger can and the side of the relay it was very hard to see, and easier to overlook. It was an oddball, a round red/green thing that tested both ways as 2.72 ohm resistor, and not as a diode at all. It would not show short on my tester or on the DMM, just the little resistance. With the Dm8 "diode" removed, the relay clicked quickly. I got so excited I forgot to listen to see if the amp was working! Here are new voltages, with NO diode - Qm26 b= .716 c= 151.mv e=1.1 mv and on Qm25 b=17.7mv c=13.46v and e=1.1mv.

Rm70 showed 39.5v on the B+ side and 25.5v on the relay side. The relay coil measured 605 ohms. I see I have some work to go, but I wanted to report the positive progress. Thank you again. Back to the project. I would post a picture if I could figure that out. How big a file should an image be?
 
Update: Got some parts ordered, and meanwhile I tacked the receiver back together and Voila! Music! Actually sounded very good, and it has not been recapped yet. I'll be glad to leave another update as I go along, but once again a HUGE THANK YOU! to all who offered help.
 
:thumbsup: Did you ever address the +36 volts on pin 4 or the power supply on the other 56000? Just curious....
 
No, Steve, did not get back to that yet. While putting the "bad" 5600 back together to hear it I popped the tuner dial string and a comedy of errors ensued...at which point the "good" 5600 became an excellent example of how the string should look, even if Fumble Fingers here couldn't make it look that way! The registration of the pointer has likely been lost, but I'll cross that bridge later.

Wonder where to look for the high voltage problem on pin 4? I have new caps ordered, and I even ordered new diodes and a new voltage regulator for Qk1 but that transistor is back ordered until February! It's an MJE15032G, so another replacement might be needed. I have NOT tested it yet, or even gotten any voltages yet, as I was too busy amusing myself with a very awkward little string! That stiff little string gave a new meaning to the phrase "like trying to push a string!"

I'll stick with it. I appreciate the follow up attention. These are fine amps, and AK is a fine forum!
 
Pin 4 problem should be bad resistor (RK2 open) or bad solder joint or crack in trace.
 
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