This is a pretty rare Blade M504 amp. Is there any literature floating around about it?
This one powers and draws about 2A idle. Backed the bias down and idles at 1A.
Amp has +-32vDC rail.
No regulated voltage. It appears the amp is trying to power the pre-amp but falls into a soft protect. I can briefly measure +-7vDC regulated on my meter but then drops like a rock to practically nothing.
There is an Output CLIP LED that briefly flashes once or twice on power-up.
I did find U33 near the center of second photo LM393 shorted: 4-8 measuring 218ohms, and 4-7 measuring 33ohms. Replaced, and no difference. I tried tracing back pins 4, 7, & 8 to various components for failures but coming up blank.
It sure is nice to see something new on my bench.
Anybody seen one of these before? I believe D8/D9 are part of the regulator circuitry; center of the first photo.
This one powers and draws about 2A idle. Backed the bias down and idles at 1A.
Amp has +-32vDC rail.
No regulated voltage. It appears the amp is trying to power the pre-amp but falls into a soft protect. I can briefly measure +-7vDC regulated on my meter but then drops like a rock to practically nothing.
There is an Output CLIP LED that briefly flashes once or twice on power-up.
I did find U33 near the center of second photo LM393 shorted: 4-8 measuring 218ohms, and 4-7 measuring 33ohms. Replaced, and no difference. I tried tracing back pins 4, 7, & 8 to various components for failures but coming up blank.
It sure is nice to see something new on my bench.
Anybody seen one of these before? I believe D8/D9 are part of the regulator circuitry; center of the first photo.
Attachments
The board seems very sensitive to heat. I wonder if there is a way to force the pre-amp to come on so that I can find faulty components? I'd rather not remove all the ICs.
It looks like Zapco/clarion amps. Does it have the op-amp that passes the regulated voltages to the preamp op-amps?
Which regulated supply are you referring to? As per the OP, the main voltage rails aren't regulated.
How does an amp "use the op-amp to switch regulated supply"?
I believe I've fixed this amp. Of course the U33 LM393 was definitely failed, and I noticed the other LM393 at U18 was not functioning correctly though it was probably OK.
I thought something was wrong near D6/D7 and then finally found R111 under two laid down ESR caps burnt up. R111 was measuring 4k but was crispy fried.
I first filled R111 with an 100ohm 1/2w, and observed +-8vDC regulated voltage. Then tried:
50Ohm: +-10vDC
10Ohm: +-13vDC <-- Stayed here.
I'm not really sure what R111 is supposed to be.. Thoughts? It connects between secondary ground and D5/6/7/8.
Amp can pass audio to speaker terminals now.
I thought something was wrong near D6/D7 and then finally found R111 under two laid down ESR caps burnt up. R111 was measuring 4k but was crispy fried.
I first filled R111 with an 100ohm 1/2w, and observed +-8vDC regulated voltage. Then tried:
50Ohm: +-10vDC
10Ohm: +-13vDC <-- Stayed here.
I'm not really sure what R111 is supposed to be.. Thoughts? It connects between secondary ground and D5/6/7/8.
Amp can pass audio to speaker terminals now.
Attachments
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Re post #6:
The regulated supply switching is done by the op-amp and supplies voltage to the differential amplifiers. See U9 on page 3 and the differential amplifiers on page 4 of the attached service manual.
The regulated supply switching is done by the op-amp and supplies voltage to the differential amplifiers. See U9 on page 3 and the differential amplifiers on page 4 of the attached service manual.
Can't speak to the specifics of the reference designators you've listed because I don't have a schematic or amp in front of me, but the LM393s in that amp are used in the following circuits:
1) remote/trigger operation
2) thermal protection, turns trigger off if the amp gets too hot
3) optical bias switching, they activate the TIL117 opto-couplers controlling the output stage bias
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U9 in this circuit is an analog voltage reference and not a switching supply. The diff amp is powered by the main voltage rails (Vamp+ and Vamp-) which is switched by the the U10 SG3525 PWM controller.