BIG problems

Yes Michael, hold the board vertical and with a small paint or chemical brush , apply it and work from the top down. We are looking for broken traces, lifted traces and solder bridges. When there is a short on the board the standard measurements may not be valid, as a problem with the board can preclude in circuit testing. Pull Q5 and test it out of circuit.
 
Michael F said:
120vac in gets me .040vdc on left output and 101vdc on right :sad2:
101vdc also present on collector of Q5
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Well now we are getting somewhere, that means you have no base drive coming from Q4 which is one of your 2N5401 devices.
 
Gepetto said:
What board do you have? PL20?
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At equilibrium the base of Q3 and Q4 should be somewhere close to 10V and reasonably the same. In your case where Q5 is good and the collector is at 100V then you should see the base of Q4 significantly lower than 10V if the front end is working for you.
 
Gepetto said:
At equilibrium the base of Q3 and Q4 should be somewhere close to 10V and reasonably the same. In your case where Q5 is good and the collector is at 100V then you should see the base of Q4 significantly lower than 10V if the front end is working for you.
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Board is a PL14a. Do you want me to re install Q5 and measure base voltage of Q4?
 
Michael F said:
Board is a PL14a. Do you want me to re install Q5 and measure base voltage of Q4?
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Sure thing. If you are not blowing stuff up then you should be able to continue to debug successfully. Remember there is 200V inside so do be careful.
 
And DC packs a much bigger wallop than AC does. You can get loose from AC when it crosses the 0 line, not so with DC.
 
STOP right here for a sec Michael... wait for my next post, please.
 
Michael F said:
Q4 test points please
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When looking at the flat on Q4 with leads pointing down the pinout is E-B-C from left to right.

Positive DMM lead on center lead (careful here) and negative DMM lead on ground.

Measure and record the base voltage on both Q3 and Q4
 
When probing the pins of TO-92's there is about 1/32 space between them. Take the positive probe and insulate the exposed part except for the last 1/16 ". Grab some heatshrink and do it before going any further. This 5 minutes will save you DAYS chasing your tail should you slip and short things.
 
laatsch55 said:
When probing the pins of TO-92's there is about 1/32 space between them. Take the positive probe and insulate the exposed part except for the last 1/16 ". Grab some heatshrink and do it before going any further. This 5 minutes will save you DAYS chasing your tail should you slip and short things.
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Or better yet if you have some mini grabber clips.
 
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