BIG problems

[Gepetto]

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.

 

[laatsch55]

Is the bias tranny trying to compensate too?

 

[orange]

I'm only jumping on that one ONCE. CARRY ON.

 

[NavLinear]

I like the middle fuse Lee.

 

[Gepetto]

I like the middle fuse Lee.

Me too. I am guessing that is Lee's ground jumper.

 

[laatsch55]

Since when is earth ground fused.??

 

[NavLinear]

Since when is earth ground fused.??

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.

 

[laatsch55]

I know you were just F*&^%^% with me!!!!

 

[laatsch55]

No OP today??

 

[Michael F]

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.

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?

 

[Gepetto]

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?

With respect to Ground Mike.

Ground on the negative DMM lead
Q5-C on the positive DMM lead

 

[Gepetto]

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?

If you have a leaky predriver you will develop heat. Are R38 and R39 good? These are the 10 ohm bias resistors.

 

[Michael F]

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.

 

[Michael F]

If you have a leaky predriver you will develop heat. Are R38 and R39 good? These are the 10 ohm bias resistors.

No heat anywhere, 10R`s are good.

 

[laatsch55]

Joe in a previous post, R38 was unattached at the buss bar, it has since been reattached.

 

[Michael F]

With respect to Ground Mike.

Ground on the negative DMM lead
Q5-C on the positive DMM lead

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?

 

[laatsch55]

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.

 

[Michael F]

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.

With or without B+/B- 200R`s?

 

[laatsch55]

Without.

 

[laatsch55]

Mike, what are you running for drivers??