Hello, I am repairing 401m. I've had it for a while (Years) and have just gotten back around to it. This one is a weird one and I'm at a loss. I am thinking that the main IC (IC2) may be faulty.
Checked the power supply and output transistors and all check out fine.
I removed Q20 and Q21 because I couldn't get the amp out of protect. Verified that there was not 5v going to pin5 but the amp is still in protect.
Applied 12v to the pwm IC and the power supply powers up fine. Verified a nice solid +/- 62v and 15v rail. Amp pulls a low 2 -3 amps at idle.
Everything outside of IC2 seems to be functional. It just thinks something is wrong for one reason or another. I'm almost tempted to short the emitter and collector on Q22 to get the relay to turn on to see if I can get audio out of it.
Any suggestions are greatly appreciated and thanks for you help~
Checked the power supply and output transistors and all check out fine.
I removed Q20 and Q21 because I couldn't get the amp out of protect. Verified that there was not 5v going to pin5 but the amp is still in protect.
Applied 12v to the pwm IC and the power supply powers up fine. Verified a nice solid +/- 62v and 15v rail. Amp pulls a low 2 -3 amps at idle.
Everything outside of IC2 seems to be functional. It just thinks something is wrong for one reason or another. I'm almost tempted to short the emitter and collector on Q22 to get the relay to turn on to see if I can get audio out of it.
Any suggestions are greatly appreciated and thanks for you help~
Is there audio on the emitters of the output transistors?
Please (and this applies to anyone who needs repair help) use your sig line to list all equipment you have, editing it as equipment changes. Include the model numbers.
Top of page, menu USER CP >> EDIT SIGNATURE
Oscilloscope (yes or no)
Multimeter(s)
Type of signal source (grounded RCA shields preferred).
Soldering iron
Desoldering pump
Power supply
2 ohm current limiting resistor (hollow cylindrical ceramic 100w preferred)
Please (and this applies to anyone who needs repair help) use your sig line to list all equipment you have, editing it as equipment changes. Include the model numbers.
Top of page, menu USER CP >> EDIT SIGNATURE
Oscilloscope (yes or no)
Multimeter(s)
Type of signal source (grounded RCA shields preferred).
Soldering iron
Desoldering pump
Power supply
2 ohm current limiting resistor (hollow cylindrical ceramic 100w preferred)
Yes.
Thanks for your help
Oscilloscope - Yes
Multimeter(s) - Yes DMM
Type of signal source (grounded RCA shields preferred). Chromecast Audio & KDC-P907 (When needed)
Soldering iron - Yes
Desoldering pump - Yes
Power supply - Yes 52amp + 2 30amp (Switching)
2 ohm current limiting resistor - 4 x 225watt 4 ohm tube type & 1 automotive headlamp for current limiting
Thanks for your help
Oscilloscope - Yes
Multimeter(s) - Yes DMM
Type of signal source (grounded RCA shields preferred). Chromecast Audio & KDC-P907 (When needed)
Soldering iron - Yes
Desoldering pump - Yes
Power supply - Yes 52amp + 2 30amp (Switching)
2 ohm current limiting resistor - 4 x 225watt 4 ohm tube type & 1 automotive headlamp for current limiting
If there isn't any significant DC on the emitters of the outputs, shorting Q22 shouldn't cause any problems. Try it but be ready to shut it down if there is a problem.
Update: I shorted Q22. Didn't have any problems. Before I put my 4 ohm dummy load on it I noticed that there was 1.5v across the output terminals. Just for giggles I installed the 4 ohm load and remeasured. It dropped to .01 - .02v. While initially I thought I was getting actual audio on the emitters I was only getting what appeared to be the top half of the audio. I will have to go back in today when I'm don't with work and retest with a pure sine wave coming into the amp. Signal is strong and clean at Q101. I will have to trace the signal from there.