Kenwood KAC-721 No sound

[mbates14]

Ran into one of these that has absolutely no sound, the offset is 2.1 to 2.3VDC on both channels, replaced all capacitors, half were leaking.

Replaced a bad emitter resistor.

Still the same thing, both rail voltages are fine. the op amp rails are fine as well. any ideas?

[Perry Babin]

Email me if you want the service manual.

babin_perry@yahoo.com

Do you have audio on pin 4 of the UPC1270 driver ICs?

If you still need help, let me know here or via email.

[mbates14]

nope. no audio there. its like the amp is stuck in mute.

I removed output transistors, same deal. Base of all outputs are +26V with outputs removed.

[mbates14]

Mute voltage is at 8V on the ribbon going to the pre-amp board.

[Perry Babin]

With the output transistors out of the circuit, the feedback loop is open so no no drive voltage readings will be of any use. Reinstall the output transistors. Do you still have 8v of mute drive?

[mbates14]

yes, and speaker output offsets are still 2V

[Perry Babin]

Pull the muting transistors. Does the audio return and the DC go away?

[mbates14]

it took forever and finally self-unmuted, but the speaker output is still sounding slightly distorted, and the speaker offset is bouncing all over the place.

[Perry Babin]

With the muting transistors in or out?

Is the signal clipped?

Post a photo of the distorted waveform.

[mbates14]

I grounded the Base to Q1 and Q2, everything works fine. no offset, no distortion, however it gets hot pretty quick and idles at 1.3amps on the 12V line.