newbie troubleshooting

[triple6]

I have been helping my father in law troubleshoot his kenwood km 106 power amp. I believe its from 1987. He was getting a hum then no sound at all to the speakers. The unit has power, all the lights are working, all the speakers and cables were checked and everything was good. Still no sound to the speakers or headphones. Any help to point me int the right direction would be greatly appreciated. THANKS

 

[bobcat]

Do you have a multimeter if so set on dc volts and disconnect the speakers and check the voltage at the speaker outs should be a few milivolts anything more and you have a dc problem let us know the results

 

[jitter]

The service manual of the KM-106 can be found here.

Wait until the text under the preview picture "This file is downloadable free of charge from the site... processing (please wait)" changes to "This file is downloadable free of charge from the site: Get Manual" and click on "Get Manual".

With the amp switched on, if you press the speaker buttons, do you hear a relay clicking or not?

 

[triple6]

I'm getting no reading on the speaker outs. I downloaded the manual, Thank you. I am not hearing the relay clicking . The protection relay is Omron G5R-2232p. Is a bad relay a common problem?

 

[djoffe]

It could be a bad relay, or it could be a protection circuit sensing too much DC on the output, and keeping the relay open to prevent speaker damage. You'd have to check at the output of the amp before it hits the relay to determine which it might be.


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[jitter]

If the speaker relay doesn't click when pressing the button, and power seems to be working, as you say, then my first suspiscion would be that the protection IC (IC1) detects a fault and doesn't switch on the speaker relay to prevent damage.

The next step would be to measure to see if the DC voltages in the PSU are present and correct. Be careful, high(ish) voltages are present and and accidental slip with a probe might cause a short and blow up components (been there, done that).
Start op page 5, section F1. D13 should output +68 V and -68 V (not stabilized, so could vary by a couple of Volts). D14 puts out 34 V which is stabilized by Q34 to 23.4 V.

If these voltages are present, then the next step would be to measure some voltages at in the input of IC1 to see if it detects a fault. Some voltages are given in the schematic. In the datasheet of the IC, you can find a table with threshold voltages for some of the pins. E.g., if the voltage on pin 2 were to exceed 0.54..0.70 V or fall below -0.23..-0.12 V, then IC1 regards that as a DC-offset fault and won't actuate the speaker relay K1.

Please make these measurements and report back what you find.

 

[lozdan]

I know this is an old post, but hope someone can help. I have a kenwood KA-550 that suddenly stopped working. After doing some research and coming across these posts. I pulled the cover off of the relay to check if it was faulty and it wasn't. As a result I damaged one of my speakers and that obviously means there is to much DC voltage. My question is, now that I know there is to much DC voltage, what component do I need to repair / replace??? Is it the PSU or .... ?????