UPDATE: Polarad 632B-1 SA repair

[orbanp]

Hello Everyone,

Recently I have acquired two Polarad 632B-1 spectrum analyzers, none of them is working.

Unfortunately I do not have the maintenance manual or schematics. I have been trying to locate one, but so far no luck.
Any help in that?

The SAs have triple conversion architecture, going up to 2GHz, and have a 1k by 8-bit digital memory for the screen, from around 1980 or so.

Unit 1 was blowing the main fuse.
I tracked it down to a shorted tantalum capacitor on the main board, that was the filter capacitor for a 12V stabilized PS. The shorted cap took out the two-way raw voltage rectifying diodes, one of them was cracked, the other shorted, and that caused the main fuse to blow.
Having repaired these now the SA powers up, but nothing on the screen.
It looks like that the first LO is working, when the frequency span is narrow and the frequency sweep is done at the 3-rd LO, the first LO can be phase locked. The phase lock feature seems to be working, when adjusting for it the "locked" LED lights up.
Despite not having anything on the screen the CRT seems to be working, when turning the unit off, a green halo/dot can be seen traveling across the screen, so it looks like the CRT heater is working and there is HV too, except the deflection is off the screen.

The second unit initially had some display on the screen, except what was displayed had nothing to do with the input signal.
My guess is that the first LO is not working.
I do get the input signal through to the input port of the first mixer, and static measurements of the mixer with a DMM indicate as if the mixer is fine. It is a high-level diode ring based DBM, made by Polarad.
Also, the first LO can not be phase-locked, like on the other machine.
Unfortunately my "best" equipment to measure the first LO signal (2.1GHz to 4GHz) is not good enough, it is a service type SA working up to 1GHz.
As of now the display on that unit is not working either (it just stopped), there is nothing on the screen, not even a hint of the beam as on the other unit.
Here my guess would be a faulty HV-unit.

Now would be a good time to have the schematics!
Without it I can see a painfully slow repair process, comparing the modules of the two instruments to each other.

Any help would be appreciated!

Thanks, Peter

[9H1LO]

contact me by email, i have the 40ghz version of this SA and have done lots of work on it, have the manuals for it in PDF

[orbanp]

Thanks for the help offered!

PM sent, your e-mail does not seem to be working from within the forum.

Thanks, Peter

[orbanp]

Hello Everyone,

I made some progress with the repair of the SAs, Unit #1 is working now!

First of all, I did find manuals.
OH6LSL, a Finnish radio amateur, posted excellent quality manuals (the scanning) of his 632A analyzer on his web site.
There are only minor differences between the A and B versions.
Many thanks for him for sharing the manuals!

There is also the service manual available on the web on the model 630, the big brother to the 632, which works up to 40GHz. While the first part of the RF-stages are different, the rest of the analyzers are pretty much the same.
Also many thanks to 9H1LO who helped with sections of that manual!

On Unit #1 the problem of not having any trace on the screen turned out to be the CRT final vertical differential amplifier being out of balance. The balance adjusting trimmer pot had a contact failure and/or was totally mis-adjusted. It is a funny looking trimmer pot, has about five turns of adjustment, but it is not the screw-type trimmer pot, it looks like a "regular" trimmer pot, just a bit fatter.
Still have to do a full performance check on that unit though.

On Unit #2 the HV PS was faulty. Some 3kV filter capacitors got leaky and eventually burned down. It also scorched the PCB material under it, I had to cut that section out, the carbonized PCB was conducting!
It is running now.
I am still left with the problem of how to measure a signal in the 2GHz to 4GHz range. It is the first LO, that I am suspecting is not there.
Any advice on that would be appreciated!
I am lacking proper test equipment for such measurements. The best SA that I have goes up to 2GHz, the one I just repaired, and a HP-6840B generator with the option to go up to 1GHz.


Regards, Peter

[DarkAvenger183]

Hello,
I bought a SA Polard 632A-1; It was described as "functional unit" but unfortunately it is defect. There is some image on screen, but it's not what it should be (see attached).
Can you please help me with schematic diagram /hints in diagnosing this equipment? I wish to restore is and have it back in working condition.
Thank you!