I recently picked up a can't-test-it-no-speakers KR-9600. Luckily, it turns on and both relays engage, but there's no sound. If I plug a source directly into main-in, I get sound out of both channels. The problem is in the preamp. Are there common preamp problems with the KR-9600? Nothing looks burnt or disconnected. I cleaned the controls and there was no change.
Kenwood KR-9600 no sound from preamp
- Thread starter sruchris
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I did more troubleshooting today..... When plugged into my 100w DBT, the DBT bulb starts bright and dims just a little, but the relays engage and I can get sound of the the main amp. When plugged into mains, no relays engage, and, of course no sound.
When the main in/pre amp jumpers are in, and we're powered via the DBT, I do hear some slight popping through the speakers when I turn the selector switch.
Does this mean I have a short in the preamp section?
When the main in/pre amp jumpers are in, and we're powered via the DBT, I do hear some slight popping through the speakers when I turn the selector switch.
Does this mean I have a short in the preamp section?
After more troubleshooting, here's where I'm at.... On the DBT, on power up, the bulb glows very bright for a few seconds then slightly dims. With a source plugged directly into Main In, I get sound but it's distorted. With the preamp/main-in jumpers inserted, I get no sound. Both relays engage.
Yes, all of the internal fuses test good when continuity testing using my multimeter.
I did more troubleshooting today and found Q15 on the power supply was bad. After replacing it, I get good clean sound out of the speakers when plugged directly into Main In. I'm still getting no sound from the preamp. Connecting the Pre Out to another stereo's Main In produces no sound. So no sound from AM, FM, AUX, both phonos and both tape monitors. The FM tuning meters do move when tuning, which is good.
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Semanon
Super Member
Lots of ways for the signal to get lost between input and the pre-amp output, so what I would do is check for continuity through all the selector switches (tone, tape monitor, both if it has A and B monitor switches, source, loudness, etc) in all positions. Classic failure of one channel is a dirty contact. Also verify that the volume and balance pots have correct and variable resistance and that all solder joints are good.
Verify power supply voltages ON the pre-amp board as noted, wires break and solder joints crack on wire wrap pins, it's entirely possible to have good voltage at the power supply and nothing on the board itself. The fact that the DBT does not dim down quite a bit tells me you probably have shorted components on the pre-amp board, the outputs are fine and within DC offset parameters since the relays operate. Check voltages at all the transistors, should give you a clue as to where the issue is.
Solder joints on the RCA connector are often cracked, but not on all inputs for only the left channel as a rule.
Best tool for this is an oscilloscope, will let you see what happens to the signal throughout the signal path by testing at each component. That is how I found the missing carbon resistor in the volume pot on my KA-88 -- signal is fine going to the pot, nothing on the other side, and no connection even after disassembly and cleaning -- no carbon track for one channel and very poor connection for the other. Still looking for a pot for it.
Verify power supply voltages ON the pre-amp board as noted, wires break and solder joints crack on wire wrap pins, it's entirely possible to have good voltage at the power supply and nothing on the board itself. The fact that the DBT does not dim down quite a bit tells me you probably have shorted components on the pre-amp board, the outputs are fine and within DC offset parameters since the relays operate. Check voltages at all the transistors, should give you a clue as to where the issue is.
Solder joints on the RCA connector are often cracked, but not on all inputs for only the left channel as a rule.
Best tool for this is an oscilloscope, will let you see what happens to the signal throughout the signal path by testing at each component. That is how I found the missing carbon resistor in the volume pot on my KA-88 -- signal is fine going to the pot, nothing on the other side, and no connection even after disassembly and cleaning -- no carbon track for one channel and very poor connection for the other. Still looking for a pot for it.
I dragged this KR-9600 back onto my desk today. It still has no sound out of the preamp. I don't see any broken wires. However, the preamp board voltages are off. Here they are with the service manual voltages in parentheses for each pin.
3: 3.6v (4.4mv)
5: -1.3mv (125mv)
7: 4.5mv (125mv)
9: -1.0mv (112mv)
11: -2.5mv (112mv)
19: 35.5v (34v)
20: -34v (-33v)
3: 3.6v (4.4mv)
5: -1.3mv (125mv)
7: 4.5mv (125mv)
9: -1.0mv (112mv)
11: -2.5mv (112mv)
19: 35.5v (34v)
20: -34v (-33v)
After more troubleshooting, I am getting sound only out of the left speaker when I have a source plugged into the Tape Monitor 1 and 2 Play inputs. When powering on, should I hear the reed relay on the mic board click? I'm not hearing it. I'm only hearing the two main relays click in about 5 seconds after power on.
I should be getting 10v on pin 21 on the mic board, but I'm only getting 2.5v. That's why the reed relay isn't energizing.
I should be getting 10v on pin 21 on the mic board, but I'm only getting 2.5v. That's why the reed relay isn't energizing.
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Something is drawing too much current on the other side and pulling the voltage down.
The power supplies on these are the worst.
The power supplies on these are the worst.
Here are my power supply voltages. There's definitely something wrong here. Service manual voltages are in parentheses.
After replacing DK3 and DK4, my voltages are looking better.
Pin
3 = 67.3v (67v) good
7 = -33.7 (-33v) good
9 = -9.6v (-8.2v) maybe
10 = -30.5v (-33v) maybe
11 = 2.6v (10v) bad
14 = 35.3v (34v) good
15 = 67v (67v) good
17 = 13.3v (13v) good
18 = 12.7v (13.2) good
19 = 13.4v (13v) good
21 = -15v (-13.5v) good
22 = -34v (-33v) good
23 = -67v (-67v) good
25 = 67.7vdc (67v) good
29 = -35.1vdc (-33.9v) good
30 = 67v (67v) good
33 = 26v (25.2v) good
Q5 E
Q5 C = -59v (-60.2v) good
Q5 B = -35.1v (-34.5v) good
Q6 E
Q6 C = -35v (-34.5) good
Q6 B = -0.6V (-0.55v) good
Q12 C = 17v (17v) good
Q12 B = 0.2v (0.1v) good
After replacing DK3 and DK4, my voltages are looking better.
Pin
3 = 67.3v (67v) good
7 = -33.7 (-33v) good
9 = -9.6v (-8.2v) maybe
10 = -30.5v (-33v) maybe
11 = 2.6v (10v) bad
14 = 35.3v (34v) good
15 = 67v (67v) good
17 = 13.3v (13v) good
18 = 12.7v (13.2) good
19 = 13.4v (13v) good
21 = -15v (-13.5v) good
22 = -34v (-33v) good
23 = -67v (-67v) good
25 = 67.7vdc (67v) good
29 = -35.1vdc (-33.9v) good
30 = 67v (67v) good
33 = 26v (25.2v) good
Q5 E
Q5 C = -59v (-60.2v) good
Q5 B = -35.1v (-34.5v) good
Q6 E
Q6 C = -35v (-34.5) good
Q6 B = -0.6V (-0.55v) good
Q12 C = 17v (17v) good
Q12 B = 0.2v (0.1v) good
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On the other side? Do you mean the Mic board? I cut the wire that connects Pin 11 of the power supply to Pin 21 on the Mic board and I get 35v on Pin 11.