DCP going south??

[laatsch55]

That's typical for what I see too Ray, now try 1khz and go for a clip....

 

[roccus]

That's typical for what I see too Ray, now try 1khz and go for a clip....

not over 40 VAC output on this as well Lee?

 

[laatsch55]

What is your rail voltage when she clips??

 

[roccus]

What is your rail voltage when she clips??

I will get that for you... but again not over 40 VAC for the 1khz?

 

[laatsch55]

Yeah, I got ya....

 

[roccus]

At 1khz I could not get it to start to clip till I hit 42VAC rail voltage was 75.5 VDC

 

[laatsch55]

42 volts squared , divided by 8 is 220 watts, and you are not out of rail voltage yet.... desolder one end of D9, just one end and lift it away from the board. Doing that isolates the SOA protection circuit. It looks like the protection circuit may be triggering too soon. Then run the 1khz test again, but don't go over 46 volts out, see if it clips before 46....

 

[roccus]

42 volts squared , divided by 8 is 220 watts, and you are not out of rail voltage yet.... desolder one end of D9, just one end and lift it away from the board. Doing that isolates the SOA protection circuit. It looks like the protection circuit may be triggering too soon. Then run the 1khz test again, but don't go over 46 volts out, see if it clips before 46....

D9 on the control board?

 

[laatsch55]

Correct, both channels....

 

[roccus]

OK Lee will hold off on that till tomorrow got to pull the face plate it is getting late and I gots to get up early to take care of a few things then I will check it out and let ya know what I come up with.... thanks for help hope we are moving in on the problem

 

[laatsch55]

Yep.....

 

[roccus]

Hey Lee D9 L & R disconnected.....

Right channel goes to 45.3 VAC before it starts to clip
Left channel goes to 45.2 VAC before it starts to clip

DCP never tripped on either side

 

[laatsch55]

Ok, you need to replace R25, R26 in each channel with a 13K resistor. You have 56K in there now.

 

[roccus]

Ok, you need to replace R25, R26 in each channel with a 13K resistor. You have 56K in there now.

OK those are 1/4 watt right?? I'll have to dig through my stock to see if I have them here... after they are in do I run another test with D9's out or do I put them back in and do some other test?? What is going on with those resistors where the values need to be changed from what most people run??

 

[laatsch55]

Yep 1/4 watters, make sure they are the same type as the 56K's.....1% flameproof....

Yes, put D9 back in circuit, You can test again if ya want, but this should cure it...

 

[laatsch55]

The Gain values have changed in the protection transistors that have been procured lately, this resistor change addresses that.

 

[roccus]

OK but why were the 56k resistors working perfectly for near 2 months... this problem all started when I plugged the C-1 in with bad opamps. I heard some horrible noises come out of the speakers when I turned the C-1 on and shut it down right away the opamps also cooked a couple transistors in the C-1. I was sure we would narrow this down to a damaged transistor or diode thinking the C-1 sent a nasty signal or voltage into the amp..... but you feel nothing in the amp is damaged?

 

[laatsch55]

The only way to answer that question is to pull every component and test each and every one, whether your transistors were from this batch is unknown, but this should correct the SOA circuit. I also fixed a 700 that wiped out a lot of components and was still having problems with pre-mature SOA tripping. this fix cured mine too. Give it a try Ray...

 

[laatsch55]

Your amp topped out where it was supposed to with no DCP trip by ISOLATING the SOA circuit, that tells me there is something in the SOA circuit contributing to the problem, this fixed mine....

 

[roccus]

OK.. well I don't have the resistors I need here closest I have is 1/2W 2% 12k so another wait and $7 shipping fee from mouser