This thread is to chronicle my HP 331A repairs. So far, in the inspection stage no power yet applied.
Found 2 bad solder connections on the power supply board and one of which was a sad C4 capacitor.
Both Filter caps measured about 200uf and had an ESR of 0.22OHMS. I still think they are ready to go.
The mini documentary movie - added here after completion
The thread starts here.....
Power supply board
Bad solder joint
Burned capacitor C4
Serial
First thing is to check the component chagelog in appendix C to see what steps have been done. Mine include steps 9 through 18
Mine might be exempt from Step 9 as well
Many of the single pin connectors to the board are loose, a light crimp should fix them. Not too worried about the capacitors on the other boards.
Though they will be tested as well, Ive pre-ordered replacements for all electrolytic on the main power board
On the ESR tester
Capacitors replaced, power supply is good
The following photos are before any calibration, and just testing the operation and controls of the unit.
Coax to unshielded alligator clips, no 600ohm terminating resistor
THD = .21% at 1KHZ 1V
THD = .205% at 5KHZ 1V
THD = .215% at 10KHZ 1V
THD =.315% at 20KHZ 1V
THD =1.2% at 40KHZ 1V
THD =2.2% at 50KHZ 1V using x10K * 5
THD =2.2% at 50KHZ 1V using x1K * 50
THD = 3.6% at 60KHZ
Thanks for posting this. I have a 331 as well, but I bought a Panasonic VP-7723A audio analyzer shortly after that, and the 331 is on the shelf.
The 331 is very easy to use, and I love the feel of the switches and the tuning capacitor.
What are your plans for using the 331? checking audio amplifiers?
I also have a 331 and I like it.
It is great as most of HP test gears of those times.
First thing I have done is to change the ac power connector by a standart one.
For more precision, I measure output voltage with a true rms multimeter because analogic display of 331 is NOT true rms.
It is usefull to check tube audio amplifiers (adjust of bias for instance) and sine wave oscillators.
Thanks for posting this. I have a 331 as well, but I bought a Panasonic VP-7723A audio analyzer shortly after that, and the 331 is on the shelf.
The 331 is very easy to use, and I love the feel of the switches and the tuning capacitor.
What are your plans for using the 331? checking audio amplifiers?
Here is a collection of videos of my current project. I generally work on Dyna equipment
https://www.youtube.com/playlist?list=PLK_zQ6_j4TF13qvrS3i2fw-p9trdjUhVm
I also have a 331 and I like it.
It is great as most of HP test gears of those times.
First thing I have done is to change the ac power connector by a standart one.
For more precision, I measure output voltage with a true rms multimeter because analogic display of 331 is NOT true rms.
It is usefull to check tube audio amplifiers (adjust of bias for instance) and sine wave oscillators.
Interesting... If its not true RMS what is it exactly?
Like multimeters, it measure the average value of the rectified ac voltage.
Only the later versions (339A for example) have a RMS converter.
I think these have a residual / monitor / filter (whatever it is called on the unit) output, so you can connect an external RMS meter (e.g. 3400A, DSO, DMM) anyway.
Good Thread Thanks for starting it.
I relied on a 334 for many years, until I obtained a 339.
The 333 and 334 have an extremely useful auto-balance function, which servos the fine frequency and fine phase controls to achieve null.
The 339 is great: a very low distortion generator built in, and the analyzer automatically tunes to that frequency. Most importantly, if the signal level changes within the selected range, the percent distortion function automatically re-normalizes and gives the distortion. With the 331 to 334, if you are adjusting for minimum distortion you need to re-check the input level (manually adjusting for 100%).
Voltage portion of the calibration this evening........
-25V rail +/- .25v violet
+25V rail +/- 1v red (adjusted by negative rail)
-11.3 +/- .1v A2TP1 Problem here.... adjusting pot A2R3 has no effect. Pot tested good on resistance
+8.2 +/- .5v A2TP2
+2.65 +/- .2v A3TP1
-20.2 +/- .3v A3TP2
The next board to work on......
It is impressive that those rails are still in spec. Though something is amiss with the -11v rail.
They weren't... that was post cal. They were off, out of spec, but nothing terrible
It will be interesting to see what is wrong with the -11V source.
See my post again.... Its probably C4 or C14 or Q1-4
My guess is C4 or Q1
See my post again.... Its probably C4 or C14 or Q1-4
My guess is C4 or Q1
I am thinking C-4 leaky or shorted.
lets hope its a capacitor.
That being said. And granted I only work on tube equipment, there must be a transistor that meets or exceeds the specification of the ones in the device
Most certainly. But sometimes they are not as easy to come by, for example HF Si-PNPs were common when Germanium transistors faded... but today they aren't really common anymore.
Thanks for posting. I'll be following this thread... also have a 331A, sitting unused at the moment.
Got the 331A but then found a deal on a 8903B so the 331A never got turned on beyond checking that it's working.
But would like to at least maintain and calibrate my 331A.
lets hope its a capacitor.
That being said. And granted I only work on tube equipment, there must be a transistor that meets or exceeds the specification of the ones in the device
I am confident one could be found.
A friend I know on the radio has an old Collins 75-A4 receiver from about 1954 or so. He had overhauled the radio back about 30 years ago replacing all the parts that are known for failure in said receiver. The other day he was using it and had to change to another set up because the receiver started developing problems.
The trouble was a ceramic disc cap that had gone open. He was reminded by a friend that "there are no good 60 year old caps".
While the distortion analyzer isn't that old... (yet) My experience tends to lead me to the passives before considering transistors when the problem is not obvious, but marginal like this one....