HP8591E - ADC-2V Fail ADC-GND Fail

[mio83]

Hello,

I bought this a very nice HP8591E (with TG) about 1 year ago. And I am in love with this machine.
I am a noob trying to learn RF as a hobby, and this SA helped me a lot!!!

Today, I was shocked!!     
During normal operation, the SA lost its trace and signaled: ADC-2V FAILL (weird, 2 Ls).
When rebooting (press PRESET) I also get a ADC-GND Fail for a few seconds.

Searching the web I found:
1) https://www.electronicspoint.com/forums/threads/hp-8590a-error-messages.65030/
2) https://www.eevblog.com/forum/testgear/hp-8590a-softkeys-do-not-react/msg1646432/#msg1646432

So it looks like it's a power supply issue (which, in the context of a bad news, it's possibly a good news).

As I said, I am not experienced at all with electronics, but nevertheless I want to try to locate (and possibly repair?) the issue.

Before I start opening it up, touching left-right, etc, I would very much appreciate your help and suggestions on the topic:

1) Do you have a HP8591E manual I can look at, for the schematics, etc?
2) Do you have general suggestions, etc, to locate possible capacitors problems?

Thanks a lot for your help!

[mio83]

Surprisingly enough, it started working again after 1h.
Does this provide some kind of hint?

In any case, IMSAI Guy (from the nice youtube channel https://www.youtube.com/channel/UCzxHDi9lhMwiG4XKzlJKy5w) kindly provided me with a link to the service manual, which I am sharing here in case it is useful to anybody else: http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=HP_Agilent%2FHP_8590_8592_Low_Cost_Spectrum_Analyzer

[mio83]

Hello,
some updates:

1) After yesterday's glitch, the SA didn't give any signs of problems. Good news!
2) I opened it up, following the service manual, just to give a superficial look and the interior seems quite clean.

Image1: https://www.dropbox.com/s/4vurdlrap02p7i6/20210628_103906.jpeg

and

Image2: https://www.dropbox.com/s/k5hnci39mh5ubpw/20210628_103928.jpeg

3) I checked the voltage test points and all voltages are fine (+/- 1% from stated voltage)

Image3: https://www.dropbox.com/s/r1kt6lmyozo6lct/20210628_111558.jpeg

4) Also the voltage leds are all working

Image4: https://www.dropbox.com/s/wru6z16ieg94hx4/20210628_111522.jpeg

5) Finally I removed the HP-IB board:

Img5: https://www.dropbox.com/s/m08ox6hpccc502m/20210628_104815.jpeg

and

Img6: https://www.dropbox.com/s/klo1d6u2twmball/20210628_104757.jpeg

6) and checked the battery (it dates 1992 and it was installed in 1993)

Img7: https://www.dropbox.com/s/q91qqz4s65eel2b/20210628_103954.jpeg

The battery has still 3.7V !!!


Notably: I didn't open up the power supply module, it requires quite a bit of unscrewing and stuff, so for the moment I didn't do it.

I have some questions:

Q1) I'd like to change the battery. The label says "Tadiran Lithium Inorganic battery 3.6V".
I found this part at Mouser (https://www.mouser.fr/ProductDetail/Tadiran-Batteries/TL-4903-P?qs=GedFDFLaBXFYVDjEFEzOCA%3D%3D) but it is not available. Could you recommend a replacement which is hopefully low cost and easy to obtain?

Q2) The HP-IP board (option 041) is a feature of my SA I don't need, and I might try to sell it. However on the top of the board it clearly says: " THIS BOARD MUST BE BOLTED INTO INSTRUMENT BEFORE POWER IS APPLIED ".
So I am not sure if I can just remove the board and run the SA without it, or not. Any suggestion?

Q3) Beside the battery change, what would you recommend (to somebody who is not replacing caps as his daily routine  )? Opening up the power supply module (A8)? Checking for suspicious capacitors? Or just wait until the problem presents itself again?


Thanks a lot!

[MarkL]

I would recommend, before doing anything else, to backup your correction constants as per the procedure in chapter 3 of the Assembly Level Repair Manual.

The battery can be replaced with Tadiran TL5104/P.  Do not remove the battery without doing the backup.

As for the intermittent errors, check the ripple on the power supply outputs, in particular the +15V and -15V.  There are several pages of troubleshooting hints for these errors starting on page 615 (chpt. 14).

My advice would be to NOT go replacing caps (or any component, for that matter) until you have proof they are at fault.  And I would leave the HP-IB interface in place.  I think it's just a warning not to plug or unplug the board while under power.  As far as I know the SA will operate fine without it, but you may regret getting rid of it if you ever want to use HP-IB to download traces or remotely control the unit in the future.