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Kenwood KR-7200 won't come out of protection

Johnny_Law

Johnny_Law

o.O
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I think I've narrowed it down to Qe13 on the main amp board but I wanted to run it by those with more experience before I figure out the replacement. (If I'm placing an order from Mouser I'll probably replace the others too because why not ... )

I've referenced a couple threads in the course of the diagnosis, namely:
http://audiokarma.org/forums/index....7200-high-dc-offset-relay-wont-engage.554842/

Basically, I turn the power on, everything lights up, but there's no *click* of the protection relay, and I'm getting no sound whatsoever out of the speakers. I haven't measured DC resistance because I'm pretty sure it's just the protection relay seeing too much voltage.

Namely, I read ~50V at pin 14 coming into the protection board, so I kinda figured that has to be what's wrong.

I replaced De6 with a 1N4004 just in case.

Now, here are my measurements ... I just can't figure out the E-B-C arrangement on these transistors. So instead I drew a picture of each and labeled them with what I think is EBC but I'm not sure.

To me it seems like the biggest problem is that I am definitely not getting 0V out of the emitter of Qe13. Instead it looks like ~23V which seems to be the cause of the jacked voltage at the relay.

Would love it if you guys could take a look at my drawing to confirm Q13 is bad (left to right is Q13, Q11, Q14, and Q15):

IMG_20160727_203644343.jpg


(A better copy of the schematic is located here: http://www.hifiengine.com/manual_library/kenwood/kr-7200.shtml)

Really appreciate any help. Thanks in advance,
Ryan
 
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Alright I think I've narrowed it down to Qe13 but I also will replace Qe11, Qe12, Qe14, Qe15, and Ce18. Here are the components I have found that seem suitable, if anyone can quickly confirm that these are suitable that'd be fantastic (I believe all the specs match or exceed):

 
The 48VDC from the collector of Qe13 remains, so this is still staying in protection. :(

I did find that disconnecting the Qe13 emitter from the circuit board fixed the issue and caused the protection circuit to click like normal, and the unit seems to work fine.

I don't want to permanently disable the protection circuit ... any thoughts? Did I use the wrong component for Qe13? I suppose, of course, something must be up with Qe13. But I don't know what else I can do other than order another transistor.

Really hoping someone can weigh in!
 
i need to see the schematic really
reading through the lines . the relay voltages will be high if not activated ,
removing the transistor defeated the protect circuit .
see what dc volts are at speaker terminals first .
 
Pulled Qe13, it was open from B to C but had reverse voltage from E to B. Replaced it with one of the old ones I pulled after testing it, (obviously not the factory correct part) now it comes out of protection. Yay!

However, now I am getting weak speaker output and DC offset issues. I'm at -35mV in the right channel and -68mV in the left. The volume is extremely low. Back to the drawing board.

It's strange since when I had Qe13's emitter totally out of the circuit board, I was getting nice strong output from the right channel.

So I guess the to-do list is:

(1) Order another replacement for Qe13
(2) Figure out what's up with the DC offset / low speaker output
 
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It was just dirty. This morning I removed the bracket to get the board back out, and it came back to life. So I rubbed some 0000 steel wool on the connections and sprayed with some de-oxit connection lube. Came back to life, then died again with the FM Muting button, so that got some de-oxit as well. Now it's up and running and sounds great on all channels!

The only remaining issue is that the A + B and A + C speaker selection locations are dead, but I will call this one finished.
 
Johnny_Law said:
The only remaining issue is that the A + B and A + C speaker selection locations are dead, but I will call this one finished.
Click to expand...

If you're doing this test with just one pair of speakers connected, that's probably not a problem. Kenwood tended to wire the A + B speaker circuit in series, and with just one pair connected it's an open circuit.
 
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