HP 10811A repaired

[@philsanalogbasement]

Thanks for the vid. I remember watching this a long time ago and when I went to adjust my 8644B's 10811 this morning (just purchased and repaired a 53310a, and am currently in adjust everything mode) I was having similar symptoms and this came to mind. It did turn out to be the problem. Works perfect... thanks!

[@CraigPetersen12f36b]

Glad it helped, I have only come across this issue once or twice over the 4 to 5 years I have been purchasing used gear. At first, I thought it was a cold solder connection but was relieved that it was just a lose jam nut.

[@markgreco1962]

That’s some good work.

[@uploadJ]

I think I have one of those that is problematic owing to aging in a GPS disciplined time base ... one of the famous HP timebases used for CDMA base stations 30 yrs back.

[@W6EL]

Can you comment on the waveform shape coming off the riser board via the BNC? Mine looks kind of nasty, not at all like a sine wave but more like a lumpy square wave. Also do you have a link for the SM for that particular riser board? I could not find one for that version, which both our counters appear to have. Thanks for any info you can provide! -E de W6EL

[@CraigPetersen12f36b]

The riser card (A3 board) I am using came out of a HP 5328A (surplus military unit) I had for some 23 years till one of the pass transistors on the 15 volt rail failed. I use it to test both 10811A and 10544A references. The squarewave seen on the scope is the result of the oscillator passing through U2 and to buffering transistor Q1, a SMA to BNC pigtail then sends this to the back of the instrument. Even when the 5328A was in service I remember the waveform always looking like that at the 10MHz output jack. You should be able to find a schematic for the A3 board in the HP 5328A service manual. All this info is on page 8-25, at least in my HP 5328A service manual. Hope this helps, thanks for watching.

[@W6EL]

@@CraigPetersen12f36b Thank you! I don't know how I missed that in the SM, it was indeed right there. I too have the surplus military unit and iirc one of my 15v rails went south due to a bad op-amp. I also replaced the zener diodes in the +/-12V house keeping voltage with 7812 and 7912. The current is only about 32mA, really does not deserve the stock circuit, which consumes several watts 24/7. I have two of these counters and both had this horrible scorched look under the 12V dropping resistors, plus the zener solder joints were starting to look quite stressed. Anyway, that is my 5328A story. Keep up the great videos. Can't believe I found someone working on the same thing at the same time. --E de W6EL