HP Infinium 54845A strange problem need help!

[analogRF]

I've got an older HP branded 54845A which was failing several tests and all calibrations. I have fixed everything up. Replaced the hard drive with a compact flash, fresh install of the software and all the upgrades up to V4.5 and added memory (64MB now from 16MB before). Cleaned up the ADC ASICs and replaced an on board regulator chip and a couple of capacitors (on acquisition board) and now the scope passes all self tests (multiple times), passed all calibrations and everything is honky dory except a peculiar issue that was also there in the beginning when I got the scope (it was win95 and SW V3.72)
As you can see in the pictures, when the graphic display is enabled, all is fine and the scope works perfectly as far as I can tell. As soon as I disable the graphic display (top right corner) the waveform is cut into pieces as you can see. The issue is very visible on fast time bases but it also exists on slow time bases specially with low frequency square wave it is very visible.
For the life of me I cannot figure out what can be wrong with it. I don't think it is the acquisition board. When I got the scope I thought it was a software/driver issue so I replaced the clunky noisy hard drive and upgraded the software but the problem persists. The only hardware issue I can think of is the display board on the PCI slot but what is in there to test?
Can someone with this model scope please check and see if the scope shows the same waveform when the graphic display is disabled?

[AJ3G]

Hello:

Wonder if you figured out what was causing this problem. I just posted the same exact issue with another 54845A.

[analogRF]

the problem was in the HP graphics interface board (sitting next to the video card) which connects to the acquisition board.

I made an extender and took it out and probed around but unfortunately I could not find the problem and there were several
custom programmed PLDs on that board too...anyways, long story short I found that board on ebay for $30-40 (don't remember exact value)
and replaced it and the scope worked perfectly.

that original interface board had a LOT of bodged wires going around but they were all clearly factory made. it looked like
a very early test board on somebody's bench at HP!