This voltage shouldn't be present without remote power. If your circuit resembles the D3 schematic posted then try and find the equivalent of Q21 and post the voltage on all 3 pins in format:
E:
B:
C:
E:
B:
C:
Power to sg3525a pin13 (vcc) is fed from b+ through diode d31. Sg3525a pin15 (vcc) is a 56uf 25v to ground.
Pin 15 is not obtaining it's voltage out of thin air. Are you visually obtaining it's connection point? Or walking the PCB out with your meter?
I have not worked on one of these but multi-layer boards are a thing in car audio. My experience is with the older generations of these amps and the Earthquake D3. Which is close but my attempts to determine how close in this thread are hit or miss. You mentioned it's more like the Fusion but the Fusion schematic I have here uses a 494 not a 3525. My ability to walk you through this has become limited. You need to find the voltage source for this pin and determine why it has voltage with no remote applied.
I have not worked on one of these but multi-layer boards are a thing in car audio. My experience is with the older generations of these amps and the Earthquake D3. Which is close but my attempts to determine how close in this thread are hit or miss. You mentioned it's more like the Fusion but the Fusion schematic I have here uses a 494 not a 3525. My ability to walk you through this has become limited. You need to find the voltage source for this pin and determine why it has voltage with no remote applied.
He was referencing the bridge rectifier and voltage regulator for the fusion. The earthquake is deffinately way closer. I have continuity between pin 13 and pin 15 of the sg3525. So it's getting voltage how I explained. I visually inspect motherboards then check and double check with dmm. I also use a flashlight from the other side of the board for some of the not so obvious stuff.
Fair enough. But the D3 schematic doesn't source VCC to B+ via a diode. In fact, the way it's being explained here the PWM control chip is powered up at all times. Do you believe that's true?
I double and triple checked every component on the board with dmm. The sg3525 is always on with b+ and b- connected
Without a valid schematic or the board in front of me I can't help you trace the circuit out. I can only tell you what direction to go. Based on the voltages you posted I suspect a component leaking B+ into the remote line. I know you feel it's designed this way. But I can't recall every seeing an amplifier with constant power where it's being displayed. This is the best I can do from here with what I have to work with.
If you want to post a CLEAR photo of the entire BOTTOM of the PCB and the entire TOP (One of your photos was blurry) then I or someone else may be able to visually follow the line. Perry may have some valuable suggestions as well.
If you want to post a CLEAR photo of the entire BOTTOM of the PCB and the entire TOP (One of your photos was blurry) then I or someone else may be able to visually follow the line. Perry may have some valuable suggestions as well.
As of this moment, he has 11 volts on the VCC pin of the 3525 without the remote applied. He has about 8 volts on the VCC of the comparator driving the protection LED. Also without remote voltage.
Funny you said that. I went down this morning cause I was wondering why all the other op amps had power and it was shorted. Will replace shortly.
i Replaced q20 and the amp is working good. getting a power supply toroid making noise that is audible through the speaker as well. although i do have 3 output fets missing. please listen to attachment.
It definitely is in the speaker as well. Gain or frequency does not change it nor does putting pressure on any part.i have not tries heating any parts but I can. The only thing I found that affects it is input voltage higher voltage is louder noise.however I do have 3 fets out of the amp. It's the right toroid making noise not the left.