Inverted back plates build

Like I said Glen, time for Joe...I do not know, other than it's related to the negative drive...
 
It's the soa protection circuit. Lifting one leg will take it out of circuit....
 
Ok I have lifted the anode end of d9 l&r
Result no change

What we have is the trailing edge of the bottom only sine wave breaks into multiply lines on scope

This happens both channels with or without both banks of fuses installed at about 1.5-2 volts output into 7 phm load.
Leads to the DCP board were removed and testing done pre DCP with same results

Before I wholesale change components I want to answer these


Question is the what they call oscillation

Question best connection on control board to scope output to back plates #6 or PNP to see if distortion is comming from that?

Question could this result from one of the four caps mounted on the bridge rectifier?
 
I just tried to rule out the bridge rectifier .

Test connect output to scope before DCP and powered off the amp with oscillation showing on scope.

I then turned off the main power.
The wave did not change as the cap discarged.

So I have ruled out the power supply for now.

Interesting NOTE as the caps continue to put out current at the same level the distortion disappeared just prior to full discharge.

Next step is replace the power caps after seeing what the voltage is over caps were this change happens. I will have to condition some new ones I got from Dennis today and then try thoughs.

Any input is much appreciated. If this sounds wrong please let me know
Glen
 
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Have you scoped the signal path starting at the input of the op-amps?
 
grapplesaw said:
I just tried to rule out the bridge rectifier .

Test connect output to scope before DCP and powered off the amp with oscillation showing on scope.

I then turned off the main power.
The wave did not change as the cap discarged.

So I have ruled out the power supply for now.

Interesting NOTE as the caps continue to put out current at the same level the distortion disappeared just prior to full discharge.

Next step is replace the power caps after seeing what the voltage is over caps were this change happens. I will have to condition some new ones I got from Dennis today and then try thoughs.

Any input is much appreciated. If this sounds wrong please let me know
Glen
Click to expand...


The wave form cleans up with caps down to 15 volts dc

I may just build a new control board and swap this on out for now. To many variables!!!
 
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