When I got the amp the first thing I found was a film cap burned apart at I think C112 which is connected between the two speaker terminals. I have replaced it with a temporary cap until I troubleshoot it a little more.
When I attempt to power the amp up through current limiting resistors, the only thing I find out of place on the 494 is pin 4 is above 3.5V and of course pin 9 and 10 are off.
If I adjust my power supply up a bit to ~14.8V to ~15.1V the amp will bounce in and out of protection. The amplifier's power supply will run enough to charge the rail caps to +/- 103V, but it never stays on long enough to get the +/- 15V on the ICs.
I only find a 10K ohm resistor between pin 4 and ground. I decided to take pin to ground bypassing the resistor. Upon powering it up, amp is still in protect, but pin 16 is now at 4.9V and pin 13, 14, 15 are now at 1.5V.
So something is dragging the 5V regulator down now before jumping the resistor it was 5V.
I think the 494 is damaged or is it still something else because pin 16 is now so high? It was ~2.9V before jumping pin 4 to ground.
When I attempt to power the amp up through current limiting resistors, the only thing I find out of place on the 494 is pin 4 is above 3.5V and of course pin 9 and 10 are off.
If I adjust my power supply up a bit to ~14.8V to ~15.1V the amp will bounce in and out of protection. The amplifier's power supply will run enough to charge the rail caps to +/- 103V, but it never stays on long enough to get the +/- 15V on the ICs.
I only find a 10K ohm resistor between pin 4 and ground. I decided to take pin to ground bypassing the resistor. Upon powering it up, amp is still in protect, but pin 16 is now at 4.9V and pin 13, 14, 15 are now at 1.5V.
So something is dragging the 5V regulator down now before jumping the resistor it was 5V.
I think the 494 is damaged or is it still something else because pin 16 is now so high? It was ~2.9V before jumping pin 4 to ground.
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Finally got electricity, internet, and time.
The 10K ohm resistor at R33, connected to Pin4 was open. Replaced that and lifted Q4. Power supply is up and running I have +/- rail, +/- 15V, and +/- 5V. Protection LED is still lit.
I checked for DC on the various legs of the op amps. Ended up replacing a TL072 and I now have audio signal all the way to the audio driver board. Protection LED is still lit, relays are not engaging and no audio is present at the output inductors.
Out of time for the night but my next planned step is to disable the two IR21844 and check for signal there.
Attached is picture of the audio driver board.
The 10K ohm resistor at R33, connected to Pin4 was open. Replaced that and lifted Q4. Power supply is up and running I have +/- rail, +/- 15V, and +/- 5V. Protection LED is still lit.
I checked for DC on the various legs of the op amps. Ended up replacing a TL072 and I now have audio signal all the way to the audio driver board. Protection LED is still lit, relays are not engaging and no audio is present at the output inductors.
Out of time for the night but my next planned step is to disable the two IR21844 and check for signal there.
Attached is picture of the audio driver board.
Attachments
Just an update to this thread.
After not finding anything definitive as to why the amp would be in protect, I found that the LM293 located on the little board behind the audio driver board was defective which was putting the amp into protect as well as shutting down the IR21844's. I replaced the LM293 with a 393 and re-connected Q4 on the power supply board.
The amplifier powers up, comes out of protection, relays engage, and I have clean audio signal out.
After not finding anything definitive as to why the amp would be in protect, I found that the LM293 located on the little board behind the audio driver board was defective which was putting the amp into protect as well as shutting down the IR21844's. I replaced the LM293 with a 393 and re-connected Q4 on the power supply board.
The amplifier powers up, comes out of protection, relays engage, and I have clean audio signal out.
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