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?
Replaced a bad emitter resistor.
Still the same thing, both rail voltages are fine. the op amp rails are fine as well. any ideas?
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.
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.
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.
I removed output transistors, same deal. Base of all outputs are +26V with outputs removed.
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?
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.
With the muting transistors in or out?
Is the signal clipped?
Post a photo of the distorted waveform.
Is the signal clipped?
Post a photo of the distorted waveform.
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.
That shouldn't have affected the DC offset unless it also pulled down the voltage on the bases of Q3 and Q4. Did that happen?
The bias may be a bit high for it to run out of the heatsink.
The bias may be a bit high for it to run out of the heatsink.
The DC on the outputs was causing increased current flow through the outputs (with speakers connected) which could cause them to heat up.
removed Q3 and Q4, offset is now gone, the Mute signal coming out of the pre-amp board jumped from 8V to 13V.
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