HP 54542C scope display problem

[Stray Electron]

  I just picked up an HP 545452C 4ch color scope. The image on the screen (LCD) has yellow characters with green shading on the left of each one and purple shading on the right of each character.  It looks the picture tube mis-alignment that you used to see on the old CRT color TVs but this has an LCD screen. I've never seen an LCD have a color misalignment. Does anyone have any idea of what's going on or how to fix it? 

[wraper]

I guess what you are seeing is that each pixel consists of 3 subpixels. If pixels are large enough and you look closely, you can distinguished that characters are differently colored on the sides. But you'd better post a picture of this.

[Stray Electron]

  No there aren't bands of color within each character or object. Just a single color fringe on each side and it's the same even if it's a LARGE object like the box around the on screen menu. Every character/object has it's own two fringes but not repeating patterns like your picture shows. Also characters/objects that are a primary color (RGB) are perfect but anything that has more than one primary has one of two fringes depending on if it has two or three primary colors.

  I will try to get a picture of it but I don't know if the digital camera I have will cooperate. I've used it to photograph CRT displays but never an LCD display. 

  And BTW I just spent two hours trying out the scope.  NICE!  This is the first time that I've used a color scope, I'd like to keep it but I've already promised it to someone else.

[wraper]

  No there aren't bands of color within each character or object.

It's not like that you'll see them within object (unless magnified). The thee subpixel will look like uniform color. However, when on the sides, this continuity ends and color bands can be seen. If looked very closely (if you have good eyesight and pixels in on particular display are big enough) or with magnification, this can be noticed even on the PC monitors. Though nowadays subpixel rendering (cleartype) is used to increase apparent resolution, so might be not easy to notice unless special patterns used. https://en.wikipedia.org/wiki/Subpixel_rendering

[kc9qix]

I just looked at my 54542C, and noticed a bit of the shading effect if I turn my head and look at the screen at an angle.  Mostly on the white areas, though - I could see bluish shading on the sides.  I also noticed it with magenta lines, though not as much as the white lines.

Do you wear glasses by any chance?  I noticed that if I take my glasses off, the effect goes away.  I suspect it's the coatings on the lenses affecting different wavelengths of light differently.  If I look at it straight, the shading also goes away. 

I also noticed that the characters on mine are white, not yellow - maybe your LCD backlight is starting to go out?  The backlight on my scope was dead when I got it, so I replaced it with LEDs.

[Stray Electron]

  Actually I do wear glasses so you could be correct, kc9qix.  I'll  try viewing it without them and see what happens and report back here.

 and BTW I won't be able to get pictures till next week but I haven't forgotten.  Also I do have very good eyesight (with glasses!) and I can easily see "subpixels" and this isn't that.

[Jwalling]

  I just picked up an HP 545452C 4ch color scope. The image on the screen (LCD) has yellow characters with green shading on the left of each one and purple shading on the right of each character.  It looks the picture tube mis-alignment that you used to see on the old CRT color TVs but this has an LCD screen. I've never seen an LCD have a color misalignment. Does anyone have any idea of what's going on or how to fix it?

I seem to recall repairing one of these with the same fault. I think it was a small flat mylar intererconnect located on the circuit board of the TFT itself. After cleaning the contacts on the mylar cable and the associated connectors, it fixed it.
Good luck!

Jay

[Stray Electron]

  An update;

    We put the 54542C aside and picked up another scope. My tech complained that the display was weak in it anyway.  But yesterday I got this scope out and powered it up and now it only displays a few vertical lines of the RH side of the screen and none of the keys respond when pressed and the disk drive never attempts to spin up.  I'm assuming that the power supply has a problem and that the scope never fully boots up. Has anyone done any troubleshooting on one of these?

[factory]

If it's the same PSU used in a number of HP 545xx scopes & some other test gear, the capacitors have a bad reputation for leaking electrolyte all over the board, if it gets under the trim pots it can cause problems too, a thorough clean of the board & recap would be advised.

A really bad example here; https://www.eevblog.com/forum/repair/hp-1653b-logic-analyzerscope-psu-in-bad-shape/

Reverse engineered schematic of one variant of these PSUs here (they have slight variations depending on what they are from); https://www.radiocollection.be/images/restaurations_img/HP54503/supplyHP54503.pdf

David

[Tomorokoshi]

Some power supply repair threads. Some are for similar, but not necessarily identical equipment:

https://www.eevblog.com/forum/repair/hp-53310a-power-supply-troubles/
https://www.eevblog.com/forum/repair/hp-54520a-psu-repair/

[Stray Electron]

If it's the same PSU used in a number of HP 545xx scopes & some other test gear, the capacitors have a bad reputation for leaking electrolyte all over the board, if it gets under the trim pots it can cause problems too, a thorough clean of the board & recap would be advised.

A really bad example here; https://www.eevblog.com/forum/repair/hp-1653b-logic-analyzerscope-psu-in-bad-shape/

David

   Wow!  I hope it's not as bad as that one!  If it is then it will probably go to the scrappers. I'm used to the even older HP gear and it never had those kinds of problems.

   Thanks for the replies.