Screen Contrast

I’m having a problem with my Quad, HW version 2.70.

I design induction heaters (fluxeon com) which are directly line powered and involve high voltage. I was using the quad to read a current transformer on a high voltage well insulated line. I’ve done this many times. In fact, I have a dedicated probe. Dedicated because the burden resistor got hot enough to melt the probe :frowning:

I was watching the current waveform when the screen suddenly went negative. That is, like a photographic negative. Colors and light and dark areas reversed. Tonight I reflashed the scope using these instructions.

That fixed the inverted colors but the contrast is still off. The screen looks perfect if I move my head about 45 deg to the left.

So my question is, is there a way to set the screen contrast? I can use the scope this way but it was MUCH nicer before.


There is control over the backlight for the screen. Most of the scope Apps allow you to vary that from quite dim to full on. That will affect overall brightness of the display but that maybe not what you want.

No, backlight adjustment is definitely not what I need. The screen looks just like my LCD monitor if I turn the contract way down. Milky and washed out. Like I said, it looks fine when viewed at an angle - just like my monitor with the contrast turned down.

I assume by the lack of answers that there is no user-accessable contrast adjustment. So let me rephrase my question.

What part of the code is the LCD initialized? At the application level or system level? I’d appreciate a hint as where to start looking. I don’t mind setting up a build environment to address this issue.

I suspect that the transient event stored some bits in the flash memory that doesn’t get initialized or initialized properly and so the re-flash didn’t remedy the problem.

Any pointers would be greatly appreciated.



I’m not sure if this could be relevant to the DSO203 or your problem in particular. I had a similar issue while designing in a TFT LCD sometime ago. The problem was simply resolved by loading the color palette table on the LCD controller.

The main low level screen initialisation and access functions are in the SYS firmware but I guess you updated the SYS as well as the APP.

The code is in lcd.c / lcd.h

I think the panel driver is

Thanks for the specificity. I’ll take a look.

Yesterday when I turned the scope on, it came up normally, ran a few minutes, went to the “negative” screen for a few seconds and then to the low contrast one. Does that indicate possible hardware failure or maybe corrupted Flash? I can easily enough flash it again.

Thinking back, I’ve used the scope in the mode in which it “failed” several times in the past. That is, scope connected to a current transformer and connected to the USB port for power. The isolation transformer (Topaz UltraIsolator) is so good that I measure only about 30 volts to earth ground using a 10megohm Fluke meter, and only microamps of current. I think that the malfunction was probably just coincidental to the connection.

Edit: I can now reliably reproduce the problem. Appears to be heat-related. Turning the scope on at room temperature results in the display malfunction in about 15 seconds. Putting the scope in the refrigerator for a nice cool-down results in about 5 minutes of normal operation before the screen malfunctions.

Any suggestions as to where to look? Given my schedule, I’ll probably just buy a new scope and donate this one who wants to tear into it but I’d like to hear any suggestings nonetheless.


That does sound like a hardware failure.

There are display modules of that screen size and with same controller available e.g.

BUT I don’t know whether it is compatible from a mechanical or connector perspective. On the other hand they are cheap.

Thanks guys for the tips on this problem.

I don’t have time to hack into the scope so I simply bought a new one. It is here and is very nice.

Rather than toss it in the bin, I’m going to give the old scope to the first person who contacts me at with a postal mailing address. I’ll even pay the flat rate postage. US ONLY, please. Don’t want the hassles of international shipping. No probes included. Seeed will be happy to sell you some :slight_smile:

Note: it’s about 1PM EDT right now. If you see this message more than a couple of hours from now there’s probably no need to reply. I imagine this thing will get snapped up quickly.

The scope is still usable as-is if it is held off to the right at about a 45 deg angle so you’re looking at the screen from the left.