Inverted back plates build

[laatsch55]

Remember rule #1??

 

[grapplesaw]

Have you swapped in an amp that has tested clean??

Clean sine at 20 volts on other unit

Test equipment is good

 

[grapplesaw]

Remember rule #1??

Why is it only distorted on the trailing edge of just 1/2 the sine

 

[laatsch55]

Ok, one more variable down...

 

[laatsch55]

Like I said Glen, time for Joe...I do not know, other than it's related to the negative drive...

 

[grapplesaw]

Like I said Glen, time for Joe...I do not know, other than it's related to the negative drive...

Then we will wait patently

 

[laatsch55]

Amen...

 

[grapplesaw]

Amen...

Going to have food and them come back to it

 

[grapplesaw]

Going to have food and them come back to it

Time to test the low level driver signal

 

[Gepetto]

Time to test the low level driver signal

See if lifting the anode end of D9 on the control board has any effect on your anomaly.

 

[grapplesaw]

See if lifting the anode end of D9 on the control board has any effect on your anomaly.

Thank you Joe
I will have to do that in the morning
I will post results

 

[grapplesaw]

See if lifting the anode end of D9 on the control board has any effect on your anomaly.

Do I lift both d9l and d9r diodes?

 

[laatsch55]

Yep....just one leg...

 

[grapplesaw]

Yep....just one leg...

Right anode end only. I will desolder and lift that leg only from board for both left and right channels. Sounds abit strange but I am not to question only do

 

[laatsch55]

It's the soa protection circuit. Lifting one leg will take it out of circuit....

 

[grapplesaw]

It's the soa protection circuit. Lifting one leg will take it out of circuit....

Thanks for that. I was curious.

 

[grapplesaw]

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?

 

[grapplesaw]

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

 

[laatsch55]

Have you scoped the signal path starting at the input of the op-amps?

 

[grapplesaw]

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

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!!!