Lift D26 & D27 (1N4148) and check for Rail to Rail output on Pin 13 IC4 and note any Vdc differences on IC4 Pins 1 & 2 and around IC5.
With the output transistors in. Monitor If they heat up shut down. Are they 200N15's?
Mike I will PM you.
Mike I will PM you.
Bumping this thread...
So, I removed those two diodes. The amplifier will start and idle, I attached a scope shot below of what I am reading on Pin 13 with the scope probe in X10 mode, so its 50V per division. However, it will not start with the speaker attached, it just pops/cycles. So, I measured the speaker output while starting, and theres a few volts DC offset there during first-start and then it goes away.
Pins 1 and 2 are both at 10.3V
If I were to fathom a guess, the condition thats causing the amplifier not to start with the speaker attached with loud popping, is probably the same condition thats triggering the protection circuit.
Once the amp starts an idles, I can connect the speaker but there is no audio.
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I did find this, which was a completely missed solder joint from the factory, and its not soldered down:
That fixed the audio problem. The amplifier is now producing proper audio. I did have to ground the RCA ground to the main ground, otherwise I get RCA buzz...
Still does not fix the startup problem with the speaker attached (10A current limited PSU) and the protection problem.
Still does not fix the startup problem with the speaker attached (10A current limited PSU) and the protection problem.
Just out of curiosity, I reinstalled both diodes after resoldering that broken joint, and now it starts up outside of protection!
It still has a pretty strong turnoff thump though.
It still has a pretty strong turnoff thump though.
Is the CSD voltage dropping immediately as remote voltage is removed?
Are you removing only remote voltage when switching the amp off?
Are you removing only remote voltage when switching the amp off?
No, I shut the whole power supply down via the bench supply, that's probably why.
I ran the amp up to near rated power, it seems to be working ok now. So, it must have only been that missed solder joint from manufacturing.
I ran the amp up to near rated power, it seems to be working ok now. So, it must have only been that missed solder joint from manufacturing.