Broken Scope CRT - dots everywhere

[szeloof]

Hi all,
As seen below I have a Leroy scope with what appears to be a broken crt or driving circuitry (low voltage?). The display is dim with the grid lines barely visible, mostly made up of dots that flash rapidly and move around the screen (no one part of the screen always stays lit except the weird streaks in the center, other than it looks like its snowing...)

Any advice on how to repair would be greatly appreciated. Thanks so much!

[szeloof]

I should mention that the scope seems to respond to front panel input (AC/DC coupling leds change, etc.)

[edavid]

There's no reason to think the CRT is broken.

This is a raster vector CRT monitor, driven from a frame buffer.  Could be a sync problem with the monitor, or a frame buffer problem, or 
You really need the service manual and a working scope to fix this.

[carl_lab]

Have you checked all internal supply voltages?

[niekvs]

There's no reason to think the CRT is broken.

This is a raster CRT monitor, driven from a frame buffer.  Could be a sync problem with the monitor, or a frame buffer problem, or 
You really need the service manual and a working scope to fix this.

If this is indeed a raster driven by a frame buffer, I would suspect the CRT or driving circuitry, not the frame buffer or anything digital, because if you look at the pattern (or lack thereof) on the display, you can see streaks of phosphor lighting up, seemingly not fitting into a regular raster.

[grumpydoc]

I thought that the 9400 used a vector display.

[Alex Eisenhut]

Is there a horizontal hold in the back maybe? 

[StillTrying]

Magnetic deflection vector graphics system 1024 x 1024 addressable points.

Schematics appear to be on here: http://www.schematicsunlimited.com/l/lecroy

Other than checking a few power supply voltages I wouldn't know where to start!

[IanMacdonald]

The dots look defocused and astigmatic. Might be an issue with CRT drive voltages, or could the scan coils have slipped back along the neck?

Not that if it's colour then you should not disturb the scan coils needlessly as realigning them is a tricky job. If they're obviously loose though then that's your fault.

[edavid]

The dots look defocused and astigmatic. Might be an issue with CRT drive voltages, or could the scan coils have slipped back along the neck?

They look fine to me, considering the intensity is cranked all the way up.

Not that if it's colour then you should not disturb the scan coils needlessly as realigning them is a tricky job. If they're obviously loose though then that's your fault.

It's monochrome.