TDS220 LCD content-dependent screen corruption

[tverbeure]

I have a TDS220 that shows occasional screen corruption where entire horizontal lines become black:



The corruption is content dependent. In the video above, you can see how it goes away when I change from sample averaging to. no averaging, or how it moves along with the location of the horizontal high-value of the square wave. Other than that, the scope works perfectly fine. The corruption doesn't always happen. It might even be temperature dependent (as in: it happens less often after warming up.)

Since it's content dependent, it might have something to do with high-frequency data lines crossing over into the hsync of the LCD?

I've already replaced all the capacitors of the power PCB, they were a leaking mess, but it made no difference, so I'm looking for ideas. Has anyone seen something similar?

[daisizhou]

https://www.mydigit.cn/forum.php?mod=viewthread&tid=292066&highlight=%E5%81%8F%E5%85%89%E8%86%9C

Please refer to the link above, the problem that occurs is very similar to your problem

[tverbeure]

https://www.mydigit.cn/forum.php?mod=viewthread&tid=292066&highlight=%E5%81%8F%E5%85%89%E8%86%9C

Please refer to the link above, the problem that occurs is very similar to your problem

Nice! That looks exactly like what I'm seeing. I'm not able to see the images in the forum, or any pages past the first one, but from the pictures that you attached, I assume the cause is capacitors on the LCD PCB itself? For now, that gives me sufficient information to proceed.

Thanks!

[daisizhou]

Find those capacitors and replace them

come on

[tverbeure]

I will... once I'm done with this setup:

[daisizhou]

It looks like you're hooking up a logic analyzer to analyze the signal?
I don't know what problem you encountered.

By the way, those capacitors are in the LCD part

[TinLethax]

Tapping the bus ? Seems interesting to reverse engineer those extension card. I've seen someone replicate the TDS2CM module. I personally want to reverse engineer the TDS2MEM (Cuz I have one). But I'm more focus on trying to upgrade my TDS1012 to 200Mhz via flash dump mod.

P.S. sorry for off-topic 

[daisizhou]

Tapping the bus ? Seems interesting to reverse engineer those extension card. I've seen someone replicate the TDS2CM module. I personally want to reverse engineer the TDS2MEM (Cuz I have one). But I'm more focus on trying to upgrade my TDS1012 to 200Mhz via flash dump mod.

P.S. sorry for off-topic 

Can TDS2012C be upgraded?

[TinLethax]

Can TDS2012C be upgraded?

Probably. The PITBULL hack is not gonna work as the firmware of the model with letter suffix is newer than the one without letter suffix (Tek probably changed the factory programming password). But there's a way that you can dump the main Flash memory, modify the model ID and tinkering with the calibration value. You can check it out here : https://www.eevblog.com/forum/testgear/tektronix-tds1000b-series-hacks/ You will need the TL866 programmer and the TSOP 48 adapter.

Note that two channel model cannot upgrade to 4 channel model.

[tverbeure]

It looks like you're hooking up a logic analyzer to analyze the signal?

That setup is just for reverse engineering, not related to the screen corruption.

By the way, those capacitors are in the LCD part

Yup, I disassembled the LCD soon after my previous message. Found the 3 caps, now looking for a suitable replacement. They don't make these kind of components anymore (through-hole inside an SMT enclosure), but I think I can just make do with a tiny through-hole cap.

Edit: just noticed that your pics indeed show how they're using regular electrolytic caps as replacement, so I'm on the right track.

[tverbeure]

Tapping the bus ? Seems interesting to reverse engineer those extension card. I've seen someone replicate the TDS2CM module. I personally want to reverse engineer the TDS2MEM (Cuz I have one). But I'm more focus on trying to upgrade my TDS1012 to 200Mhz via flash dump mod.

Yeah, the TDS2MM module has been reverse engineered before, but I needed an excuse to use my HP 1670G logic analyzer and want to go deeper. E.g. checking if I can make SW modifications, add USB interface, stuff like that. Don't expect anything to come from it though, it's one of many parallel projects...

It's also a way to learn the advanced trigger and storage features of these kind of logic analyzer. You can enter complex FSM through the GUI to grab just the data that you want. It's fun to play with.

Previous efforts:

Reverse engineering: https://www.eevblog.com/forum/testgear/reverse-engineering-tds2cmtds2mm/msg4040995/#msg4040995
Design files: https://www.eevblog.com/forum/testgear/enable-fft-function-on-tds210tds220tds224

[TinLethax]

It would be cool if we can come up with more modern TDS expansion board. These scope despite being old it still gets the job done.

[tverbeure]

Find those capacitors and replace them

come on

Done!

https://tomverbeure.github.io/2025/11/03/TDS220-LCD-Corruption-Fix.html

Thanks again for the info on that Chinese forum. I don't think I'd ever have figured that out by myself.

[daisizhou]

Nice .good job

Currently, your LCD monitor doesn't appear to be aging, but I estimate that in a few years, a distant spot may appear on the screen and gradually increase in size.

However, that's alright. You remember that simply replacing the polarizing film in front of the LCD screen will restore it to its original state. This is likely an inherent problem with this particular LCD screen model(Adhesive aging); it's just a matter of time before it occurs.