Hi all,
I am new here, been working on repairing this old HP volt meter. I also have a thread going on antique radio forum.
Short story on this meter, it is a parts meter I bought to repair my once (and now again) working HP3440A, that I damaged while adjusting the -8.000v reference (screwdriver slipped and touched the back of A2
). The meter then stopped functioning. I used A2 from this parts unit and installed it in my good meter and it is now functional, so I know the problem is in A2, but there are other problems with the parts unit. I would like to get it going if possible.
I have verified the voltages out of the PSU per 5-17 in the manual.
I have verified 400hz out of the oscillator per 5-18.
I
do not get a reset pulse per 5-32.
I
do not get any waveform out of A2TP1.
I
do not get a "narrow positive pulse" out of A2CR5B on my scope (I am also not certain what a "narrow positive pulse" is but I get nothing on the scope.
Voltage readings per table 5-6:
A2Q1: -.672
A2Q2: -1.33
A2Q3: -.519
A2Q4: -.321
A2Q5: -.734
A2Q11: -.378
A2Q12: -.832
A2Q13: -20.5
This is the extent of my testing so far, and has revealed some problems. A2Q1-5, all voltages are low. I removed Q4 and 5 and tested them out of circuit with the diode check function on my DMM and they seem fine. I wonder if some other issue might cause all the voltages to be low on these transistors? A2Q11-13 seem to read mostly in spec.
I am interested in ideas on where to go next. Am I at the point of just subbing in transistors and see if things change? Is there a more thoughtful way to approach these problems?