HP8566B Display fault

[TSL]

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/TjZjwrJvDpDh4DLU9

Has anyone seen this before ?


thanks

Tim

[0culus]

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.

[pbarton]

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?

[0culus]

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.

[tkamiya]

Looks like it had too much to drink..... 

[TSL]

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.

regards
Tim

[tkamiya]

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.

[TSL]

Hi All,

I've fixed the 8566B display issue

Thanks 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/TjZjwrJvDpDh4DLU9

With 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 OK

cheers

Tim