BIG problems

Mike
I think you are at the predriver only level right now. Make sure that you do not have a leaky predriver in the upper half location on the right channel. If you have a leaker, you will be developing some heat in the right hand channel heatsink as the lower transistor tries to compensate.

A good clue to a working board is to measure the voltage at the collector of Q5 on the right hand channel. If your control board is working properly, you will have a negative voltage on the Q5 collector trying to compensate for the positive voltage on the output.
 
I'm only jumping on that one ONCE. CARRY ON.
 
laatsch55 said:
Since when is earth ground fused.??
Click to expand...

It isn't - just having some fun. It cracked me up to see the fuse jumpered and my first thought was it was your ground connection but my second thought was to fc#k with you.

I have found fuses that were replaced with large diameter wire at work a time or two.
 
Gepetto said:
Mike
I think you are at the predriver only level right now. Make sure that you do not have a leaky predriver in the upper half location on the right channel. If you have a leaker, you will be developing some heat in the right hand channel heatsink as the lower transistor tries to compensate.

A good clue to a working board is to measure the voltage at the collector of Q5 on the right hand channel. If your control board is working properly, you will have a negative voltage on the Q5 collector trying to compensate for the positive voltage on the output.
Click to expand...

The transistor terminology is confusing me, do you refer to Q`s 11 and 12 as pre drivers?
If so, I could not tell you whether one is leaky or not, would you suggest swapping the two channels Q 11 and Q 12 to see if the problem follows suit?

As for measuring Q5 collector voltage, what is the other measuring point?
 
Michael F said:
The transistor terminology is confusing me, do you refer to Q`s 11 and 12 as pre drivers?
If so, I could not tell you whether one is leaky or not, would you suggest swapping the two channels Q 11 and Q 12 to see if the problem follows suit?

As for measuring Q5 collector voltage, what is the other measuring point?
Click to expand...

With respect to Ground Mike.

Ground on the negative DMM lead
Q5-C on the positive DMM lead
 
Michael F said:
The transistor terminology is confusing me, do you refer to Q`s 11 and 12 as pre drivers?
If so, I could not tell you whether one is leaky or not, would you suggest swapping the two channels Q 11 and Q 12 to see if the problem follows suit?

As for measuring Q5 collector voltage, what is the other measuring point?
Click to expand...

If you have a leaky predriver you will develop heat. Are R38 and R39 good? These are the 10 ohm bias resistors.
 
OK, sorry for the retarded questions.. please bear with me. I just got home from work, give me a few minutes and I`ll report my findings.
 
Joe in a previous post, R38 was unattached at the buss bar, it has since been reattached.
 
Gepetto said:
With respect to Ground Mike.

Ground on the negative DMM lead
Q5-C on the positive DMM lead
Click to expand...

Quote Originally Posted by laatsch55 View Post

" Take the dbt out of circuit and briing the variac up to 80 volts. Then see what you have bias and DC offset."

I`m still in that mode, I have not brought the variac up beyond 90v without DBT.
Should I revert back to DBT/Variac combo?
 
As long as rail voltage is over 60, it's probabaly ik. I'd like to see you take the variac to 100% without the DBT in circuit.
 
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