F5T how to test outputs

[BigE]

HI. It'seems been a while.

I'm about to repair my blown F5T. I used the store boards.

Is there a way to check the health of an output board without applying rail voltage? I know I have blown some outputs, I just don't know which....

Any ideas that let me test the whole board at once?

Thanks!

 

[Zen Mod]

diode test on DMM, then - to be sure- mosfet matching jig

no free lunch there

 

[BigE]

Thanks!

 

[BigE]

I am guessing that the mosfet matching device can be used on the entire board?

If the current draw is non-zero, from the initial condition ( 0V @ gate) then I know that at least one FET is shorted.

On the other hand, if is zero and appears to operate, I know at least one MOSfet is ok... the other may be open. Do they fail like that?

I strongly doubt that it is feasible to break the diodes, given this implementation -- the OP transistor will short well before diode damage territory.

 

[Zen Mod]

these (input) JFets are depletion devices , so say normally ON - when gate is at same potential as source

these Mosfets are enhancement devices , so say normally OFF , when gate is at same potential as source

so , you need both JFet matching jig and mosfet matching jig , and these two aren't the same

 

[BigE]

My concern is *only* about the output board.

 

[Zen Mod]

well , there is clearly difference between JFet and MOSFet ;

however , when you say FET , ppl usually take that as JFet

 

[BigE]

Sorry zen. I rewrote it so many times I thought I left in mosfet. I did leave in output though. I'll be more clear next time!

Thanks again