HP8566B Display fault  - Page 1
Forum section: electronics / repair

author: TSL
author_rank: Regular Contributor
timestamp: November 12, 2019, 10:35:19 am
content: Hi all,I've just turned on my 8566B to do some work and the display is all weird!I don't know how to describe it so I took some video of what's happening, you can see that here...https://photos.app.goo.gl/TjZjwrJvDpDh4DLU9Has anyone seen this before ?thanksTim

author: 0culus
author_rank: Super Contributor
timestamp: November 12, 2019, 10:55:10 pm
content: I haven't seen this symptom before, but it *could* be something going bad in the digital circuits that drive the display. If I recall correctly, the stuff shown on the display is fully digitized, so corruption in the readouts, traces, and graticule could be related to that.

author: pbarton
author_rank: Frequent Contributor
timestamp: November 12, 2019, 11:59:32 pm
content: Strange, looks like its working correctly 60% of the time and its failing 40% of the time.When its failing, it appears to me as if the X and the Y are collapsing, the same amount, at exactly the same time.No problem with the Z axis or the CRT high voltage.The X and Y, display D/A converters probably have a common Reference Voltage?If this common D/A converter Reference Voltage is collapsing (40% of the time), then you could end up with your symptoms?

author: 0culus
author_rank: Super Contributor
timestamp: November 13, 2019, 12:03:42 am
content: Could be bad caps too. I have one IF/display in service with a 66A RF section that has a barely perceptible wobble that goes away after warming up. This might be an early symptom of what yours is doing.

author: tkamiya
author_rank: Super Contributor
timestamp: November 14, 2019, 11:56:14 pm
content: Looks like it had too much to drink.....

author: TSL
author_rank: Regular Contributor
timestamp: November 15, 2019, 12:42:01 am
content: It does look drunk doesn't it!I've had some interesting responses on the HP-Agilent-Keysight list pointing me towards C2 on the PSU for the display unit on board A1A10.And there are a few other nominated PSU caps to go take a look at.Hopefully I'll get to look at it this weekend once I extract the SA from the mountain of gear sitting on top of it.I'll report back with detail and pics once I find the fault.regardsTim

author: tkamiya
author_rank: Super Contributor
timestamp: November 15, 2019, 01:25:57 am
content: I think the grid, waveform, and annotations are all generated separately. So at least one of them something reeeeeeally good to drink. Rest of them had tea.I have some spare parts for the display unit. If you run into situations you need proprietary parts, let me know. I'll see if I can dig that out and send it to you.

author: TSL
author_rank: Regular Contributor
timestamp: November 23, 2019, 09:04:16 am
content: Hi All,I've fixed the 8566B display issueThanks to a chap on the HP Agilent list for pointing me at C2 on the A1A10 board. That was the culprit.You can see it on my cap tester here...https://photos.app.goo.gl/TjZjwrJvDpDh4DLU9With an ESR of 11K and its new capacitance of 17nF I'd say it is quite buggered!I took the opportunity to check other caps around the box and they are OKcheersTim