Products > Test Equipment
Tektronix TDS744 Color Display issue
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AVGresponding:

--- Quote from: argile_tile on February 24, 2023, 10:02:30 am ---Since white appears in pictures I will disreguard "blue".  You don't have a blue screen (crt rgb issue).

It appears to be a test pattern.  Does it occur during boot?  If so then you are "locking up" during boot.

Is this a spam post?  Posting some weird pattern to stir everyone's heads?  You posted a blue pic then later a pic clearly of another color.  Wasting readers time?

--- End quote ---

Please don't post criticisms here if you have no knowledge of the subject. These scopes don't use an RGB tube; they use a white mono tube with coloured LCD shutters synced to give the illusion of a colour screen. The problem the OP is having is a known issue.
TERRA Operative:
Yup, that's a bad LCD shutter.

The shutters work as a single pixel the size of the entire screen for each of red, green and blue.
Any partial colour defect is not due to the electronics (which only drive the entire single pixel for the respective colour either on or off) rather it is due to a known problem with old shutter panels that fail as yours has.
Often it is a circular blob that will fail, but in any case it is a terminal fault.

Either find another CRT assembly (or cut a good shutter assembly from a bad CRT and replace your shutter) ‐ hardest to source and do.
Or replace the whole CRT assembly and PCB with an LCD - easier but expensive depending on if you DIY or buy a kit.
Or just leave it and live with it - easiest and cheapest.

I keep an eye out for busted up and damaged scopes to strip for spares, _
occasionally you get one with a good CRT assembly, but it depends on how lucky you are.
james_s:

--- Quote from: H1t3ck on February 23, 2023, 03:27:43 pm ---I am more optimistic than yesterday that it can be fixed.  Of course, If it turns out to be the LCD itself then all bets are off since the CRT and LCD are bonded together. 

--- End quote ---

They are bonded but they can be separated if necessary. It's somewhat common for the optical gel between the shutter and CRT to shrink slightly creating bubbles and in that case it can be removed, apparently it makes little difference in the appearance of the display. Hopefully in this case it's just a bad connection somewhere. These NuColor displays are really cool, it's a shame they didn't see more widespread use.
jayk:
I have a listing on ebay for a replacement that might work for you:  https://www.ebay.com/itm/165936361403.  Not sure how to confirm if it would work with your scope though.
nctnico:

--- Quote from: TERRA Operative on February 24, 2023, 05:29:10 pm ---Yup, that's a bad LCD shutter.

The shutters work as a single pixel the size of the entire screen for each of red, green and blue.
Any partial colour defect is not due to the electronics (which only drive the entire single pixel for the respective colour either on or off) rather it is due to a known problem with old shutter panels that fail as yours has.
Often it is a circular blob that will fail, but in any case it is a terminal fault.

--- End quote ---
I'm not 100% convinced. The image shows what looks like a perfectly shaped bar across the screen. If you look at the schematic, you'll see the LCD shutters are driven from a counter + EPROM to produce the patterns for the shutters. If one of the bits of the counter or one of the outputs of the EPROM is stuck, you could end up with a horizontal bar across the display. This could be an easy fix after all. Maybe all it takes is reseating the EPROM.
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