HM507 display not refreshing

[shridmaster]

Hi all,

Got a problem on my oscilloscope display, discontinued product so no luck on that front. Scope is the HM507 by Hameg (now Rohde & Schwarz).

When the oscilloscope trace drawing cursor reaches all the way to right, instead of clearing the display so it can redraw from the left, it keeps redrawing without clearing. When the trace moves up or down, instead of cleanly moving it leaves a "wipe" effect. This has rendered the scope completely useless.

What's odd is that if I click a button, really any button, the display will refresh. Rapidly clicking the trigger button, for example, keeps the display refreshing enough that I can actually see a trace.

I've attached pictures of it in use. One is clean trace with no signal, another is a toggled digital signal, and another is a pure sine input. You can see the wipe effect and how by the end all that's left is basically a max and min output.

Has anyone seen this before in another digital scope and where I should focus inspection?

[akimpowerscr]

The HM507 is a combiscope, I guess the problem you have is only in digital mode.

Does it operate normally in analog? You say this oscilloscope is totally useless, I do not understand this claim.

I searched for schematics for this oscilloscope but could not find them.

I believe the schematics of the HM1507 must be quite similar.
They are available in the German version of the HM1507 manual.

[shakalnokturn]

Not quite sure I get the problem either...
From your description of the issue I thought that the scope was not clearing the previous trace display before drawing the new one, as when Infinite persistance is on.

On your last photo (sine wave input?) if the input is stable in frequency I would have expected to see a big fat sine wave displayed showing all the jitter and noise.

If your second photo is meant to be a pause, burst of square wave, pause, burst of square wave, pause it looks like the trigger is working but the sampling clock (PLL based?) may be unstable.

[shridmaster]

Figured out the problem. The "env" in the screen was the tip. It's in envelope mode.

A couple of the knobs and buttons I need to fix this don't quite work, so I think I just have to disassemble and clean this up and I'll have a nice working 50MHz scope! No wonder I swiped it for $40.