Hello,
After using K2 on the potentiometers that were spluttering, I was unpleasantly surprised to see the amp go into safety mode after reassembly.
I checked the supply voltages and found:
+14V at the output of Q13 (LM317) and -14V on Q12 (LM337) for +/-15V ===> correct.
However, I'm reading +25V instead of 32V on R4 and -28V instead of -35V on R7.
R4 and R7 are fuses, and their checked value is consistent with the schematic.
If I disconnect the preamp, I find +60V and -60V across R4 and R7.
I think the problem is with the preamp, but I don't know how to investigate the fault. Any ideas welcome...
Thank you for your help.
After using K2 on the potentiometers that were spluttering, I was unpleasantly surprised to see the amp go into safety mode after reassembly.
I checked the supply voltages and found:
+14V at the output of Q13 (LM317) and -14V on Q12 (LM337) for +/-15V ===> correct.
However, I'm reading +25V instead of 32V on R4 and -28V instead of -35V on R7.
R4 and R7 are fuses, and their checked value is consistent with the schematic.
If I disconnect the preamp, I find +60V and -60V across R4 and R7.
I think the problem is with the preamp, but I don't know how to investigate the fault. Any ideas welcome...
Thank you for your help.
+-35 volts are used in the preamp as shown below:
Measure some voltage drops across the resistors to see how much current is being drawn. However much it is must account for the lower than expected voltage.
Regarding the safety circuitry, that doesn't seem to be shown.
Measure some voltage drops across the resistors to see how much current is being drawn. However much it is must account for the lower than expected voltage.
Regarding the safety circuitry, that doesn't seem to be shown.
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I made a mistake; the preamp isn't responsible for these voltage drops.
Continuing my measurements, I went back to the amp and noticed that both speaker terminals are grounded. Continuing, I also found grounds on R61 and BR2, R54, BR3, L1, among others, but I still can't determine the faulty component.
What could be the methodology for pinpointing the culprit?
Thanks for your help.
Continuing my measurements, I went back to the amp and noticed that both speaker terminals are grounded. Continuing, I also found grounds on R61 and BR2, R54, BR3, L1, among others, but I still can't determine the faulty component.
What could be the methodology for pinpointing the culprit?
Thanks for your help.
I continue to search... and I find that a transistor is in contact with the radiator because I no longer have ground when the PCB is removed, but I have not yet found which one, the contact is random when I screw back ...
There is no schematic for the protection circuit? If not, and if the manufacturer won't provide one, then I might try to reverse engineer it by inspection of the boards. Maybe the manufacturer will at least reveal what signals the protection circuit monitors? It is just DC offset at the output of the amplifier?