Have you tried to vary voltage w/o signal as Russell suggested in post #15?
I believe I have seen an issue with the UVP back in the day. Take voltage measurements around U2-TL494. Use power ground for black probe. Also check around Q28-KTC4401 and D30-1N5237B-8.2v zener diode.
The noise may be the cause of a burnt ground trace and be be why the amp is shutting down. You will have to examine the bottom side of PCB to determine. This was not an uncommon problem and is easily fixed.
I believe I have seen an issue with the UVP back in the day. Take voltage measurements around U2-TL494. Use power ground for black probe. Also check around Q28-KTC4401 and D30-1N5237B-8.2v zener diode.
The noise may be the cause of a burnt ground trace and be be why the amp is shutting down. You will have to examine the bottom side of PCB to determine. This was not an uncommon problem and is easily fixed.
The voltage around U2 are normal. Pin 3 is staying at 0v and the chip is producing PWM on 9 and 10.
So I just figured out even with no load on the speaker outputs the amp will while increasing sine wave input, start to draw excessive current and shut down at the same point everytime. Pin 3 on U2 stays at 0V, then there is a transient spike on Pin 3 and it shuts down.
So I just figured out even with no load on the speaker outputs the amp will while increasing sine wave input, start to draw excessive current and shut down at the same point everytime. Pin 3 on U2 stays at 0V, then there is a transient spike on Pin 3 and it shuts down.
Cannot get the low voltage up and running. It appears the regulators originate via aux tap on the main transformer thru D13 and D14. Have a "square wave" on trans side of diode and no voltage on the regulator side. Not sure if transformer is being driven hard enough but the main rails are ok.
D13 & D16-1N4934 are the negative full bridge rectifier and D14 & D15-1N4934 are the positive side. If you are missing D15 & D16 the rectifiers on both sides will be disabled.
When did you lose the +/- 12v and +5v supply?
Do you have any voltage at the TP's on preamp or Class D card?
If you remove the preamp board or the Class D card, is there a change?
When did you lose the +/- 12v and +5v supply?
Do you have any voltage at the TP's on preamp or Class D card?
If you remove the preamp board or the Class D card, is there a change?
Look at the U202-LM361 with an Oscope Pins 3,4,9 & 11 and measure DC volts around U200,201,202 & 203. Post voltages and screenshots.
It's possible the problem is the Drive circuit underneath the card. Q100,102,OPT100,101 & U100,101.
To check this circuit you may want to modify the Class D card, so that you can stand card upright to get to the drive circuit underneath. I have done this by bending the pins by 90 degrees on one side and extending the pins on the other with ribbon cable.
It's possible the problem is the Drive circuit underneath the card. Q100,102,OPT100,101 & U100,101.
To check this circuit you may want to modify the Class D card, so that you can stand card upright to get to the drive circuit underneath. I have done this by bending the pins by 90 degrees on one side and extending the pins on the other with ribbon cable.
Russell, you may know this, but Kamen Vasilev designed this amp. For the most part it's not a bad amp to work on but the drive circuit underneath the daughter board does add a challenge.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.