phase linear 400

Gepetto said:
If I follow correctly, you have gone from too little bias to too much bias. DId you note what you changed to get this to occur?
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no sir ... i dont know....something is so wrong with this one....i can normally figure it out ...at leadt now i just have high bias on left channel ...
 
gene french said:
no sir ... i dont know....something is so wrong with this one....i can normally figure it out ...at leadt now i just have high bias on left channel ...
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Tim had high bias as I added rows of outputs (PL back planes, WO board). It ended up being the 10ohm bias resistors on the backplane were my problem.
 
If all the fixed values(resistors, diodes, caps) are within spec, then I'd suspect the bias transistor itself.
All three leads connect to the control board, correct? Unsolder the leads from the board and swap them to other channel. Then retest.
 
George S. said:
If all the fixed values(resistors, diodes, caps) are within spec, then I'd suspect the bias transistor itself.
All three leads connect to the control board, correct? Unsolder the leads from the board and swap them to other channel. Then retest.
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i do have 4 new transistors...i changed one out...no difference...but i am sure there is / was multiple problems...i should revisit...i would be afraid at this point to install a white oak board...as the problem has changedveven swapping sides at one point...i even swapped control boards...
challenging!!!
 
Gene, many times I've had apparent issues, but they really weren't there, the issue was my test equipment settings and connection points.
Ran into this yesterday eve after bringing up my second 400 WOPL. Needed to review Joe's documentation for proper connection points and DMM settings.
Remember Joe's #1 rule, "It's often your test equipment".
 
George S. said:
Gene, many times I've had apparent issues, but they really weren't there, the issue was my test equipment settings and connection points.
Ran into this yesterday eve after bringing up my second 400 WOPL. Needed to review Joe's documentation for proper connection points and DMM settings.
Remember Joe's #1 rule, "It's often your test equipment".
Click to expand...
i have 3 meters and a cheap chinese transistor tester...i never trust one...found a bad cable last week...
 
Soooo. ...the difference between low bias and hi bias on the one channel was you swapped driver boards?
 
swapped out 2n3403 on left channel....no change....
tis93 left channel open.....changed it...a bit better....
now left bias within limits with dbt engaged....
when full ac goes up to near 450....
right channel within specs dbt or full voltage
left offset 9mv full voltage
right offset 4mv full voltage
well below the 75 limit...
all diodes test good...
i ran continuity on every trace...every joint....
all emitter resistors about either .5 or .6 ohm....
10 ohm resistor where you check bias....both 11 ohm...
did change out the 150 ohm resistors across the drivers....in a previous session...
getting there....
 
A couple places those small diodes are back to back, to test one end of one must be lifted..
 
mr laatsch....i am down to one problem...i believe ..
the biases and offsets are both fine going through dbtester.. .adjustable and well within limits....when you bypass the dbtester ie full rail voltage / amperage...left bias shoots to 450...will not adjust lower....right side is stable...
at no time does dbtester stay bright....it always dims
i believe i have a component breaking down under full rail voltage/amperage...i will never find it testing because it works when not under full load...
 
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