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KA-7300 Newbie

P

pcc514tc

New Member
I just joined Audiokarma and I'm relatively new to repairing vintage gear, so please be patient with me! I have a Kenwood KA-7300 that has various issues, so I started by looking for any obviously failed components. On the power supply board, it appears that someone in the past replaced the Ck8 capacitor, but then I notice that Rk1 and Rk2 were running VERY hot!

I found some previous threads that suggest replacing just about everything on this board. I've done some cap and resistor replacements, but I've never replaced transistors. So here are a couple of newbie questions:

  1. Is it normal for those resistors to run so hot?
  2. If not, what should I try replacing? The resistors? The electrolytic caps? Everything?
  3. I downloaded the service manual from HiFiEngine, but it's a photocopy, so I can't read the DC voltages on the posts. Would these even help? If so, anyone know where I can get a cleaner copy?
  4. Any other initial tests you suggest?
I'm sure I'll have many more questions, but thanks for your help!
 
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As a minimum I would replace all electrolytic caps on the board as well as the relay driver transistor Qk2. Use a ksc2690ays and pay attention to the pinout. Note that Ck8 is a bi-polar cap.

Yes, Rk1 and 2 run very hot, as do the zener diodes DZk1 and 2.

Clean schematic here

Capture.PNG
 
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Another question on this board -- when I first turn on the amp, the relay switches on with a very short delay (not instantaneous, but very nearly so), and a large transient goes out to the speakers. I suspect the relay should be replaced as well, but that looks rather difficult. Any suggestions or tips? Thanks!

Peter
 
Or is this why you suggest replacing the relay driver, Qk2? I realize that it energizes the relay coil, but why is it important to replace that transistor -- what's the failure mode.

Thanks again for all your great help, Al.
 
Qk2 gets replaced because the original frequently fails, rendering the amp inoperable. No other reason

Fast relay closing on power-up is normal for this amp it seems. The pop you're hearing is DC getting to the speakers before the power supply and/or amp boards settle.

Per @hopjohn, replacing Rk8(27K) with a 75K 1/2W resistor should get you about a 4 second delay.

Access to the solder side is difficult. I always replace the relay as it is a wear item, but it is not causing your pop
 
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