VOGONS


CRT and wrong colours

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First post, by vorob

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Guys, I’ve got crt monitor - LG Flatron F700P. Last time I saw these guys it was 2002 and completely forgot the experience. Wanted to try again for retro and deep blacks.

This one was kept in storage, almost new. At least I was told such…

I’ve attached one of my retro laptops and started comparing. The default brightness and contrast levels were100% for some reason, black was bright grey and only on brightness 20% it became more like pitch black.

But the most disappointing thing is colours. In bright windows environment it looked okay, but in thief II smth was wrong. I enabled clone view and even put my iPad to compare, take a look, crt it dramatically greener.

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I was able to fix it by setting rgb on screen: red 100%, blue 100%, green 70%. Thief became acceptable but in windows colours were bad.

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I don’t understand what’s going on. Screen need to heat up? It’s broken?

Reply 2 of 37, by dionb

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Also, get a second opinion in terms of VGA output. A lot of VGA output is terrible and in recent years if it's been present, it's been a cheap afterthought. Unless you're sure that the laptop gives good output to other monitors I'd consider that at least as suspect as the screen itself.

Reply 3 of 37, by majestyk

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CRT-tubes can age even when they are not used.
Assuming the signal processing circuitry is still o.k. here.
Probably the emission of the green-cathode in the tube has detriorated a bit- either during use (before you bought it) - or during storage.

Detrioration caused by long storage reverses itself in many cases when you use the monitor non stop for a longer period, like 10 hours each day for a couple of days.

If the green emission stays low, you can (disclaimer: if you are a qualified technician) disconnect all three cathode wires (RGB) at the tube-pcb and measure the voltages directly at each of the three cathodes. If the voltage at the green cathode differs from the other two the tube has deteriorated. If all voltages are about the same value, the signal processing might be faulty.

Reply 4 of 37, by vstrakh

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majestyk wrote on 2022-07-20, 08:18:

Probably the emission of the green-cathode in the tube has detriorated a bit

You meant to say "red and blue", because emission only gets down with age, making less of that color.
Since the way to "fix" issue was to reduce the green to 70%, that could mean the green cathode is in better condition than the red and blue.

Reply 5 of 37, by majestyk

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You´re right of course - the heat in central Europe is taking it´s toll it seems...
But at least the interpretation holds true:
"If the voltage at the green cathode differs from the other two the tube has deteriorated. If all voltages are about the same value, the signal processing might be faulty."

Reply 6 of 37, by vorob

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Guys, thank for your advices. First of all I’ll let it work for some time, the we will see…

Checked solid colours, on white I noticed these blobs. Does it mean anything specific? It’s hardly seen in reality, but still I wonder what that is.

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Reply 8 of 37, by majestyk

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Better skip the strong magnet thing, you could magnetize the shadow mask behind the screen and create coloured areas in the picture.
A degaussing coil operates with AC so the magnetic field changes it´s direction 60 times a second. to avoid permanent magnetizing anything.

Besides that the built in degaussing coil should do this job perfetly. Just let the whole monitor cool down completely before turning the power on again. Several cycles shoud be sufficient.
And don´t turn the monitor too often, let it sit at it´s place - away from loudspeakers and other magnets.

Sometimes the power supply of the built in coil is defective (a PTC or some semiconductor circuit). Du you hear a buzz when you turn on the monitor when it´s cold?

Reply 9 of 37, by zapbuzz

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colour profile? monitors used to have a profile up to xp i think .icm maybe there be an .icm for yours to download for better colours and stuff.
i found one on driverguide have a go with it passed AV (microsoft avira and AVG) being 2003 i couldn't say auto install for dos windows (manual can be done) but 2000 xp should auto easily with the .inf but this will give confidence its primed for use as best it can cannot guarantee.

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Reply 10 of 37, by vorob

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Guys, what’s the story behind brightness slider on CRT monitors? From what I see it doesn’t change the bright areas but it makes black look grey and that’s it.

I’ll keep it at 0%. I’m right?

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Reply 11 of 37, by rmay635703

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Brightness on most properly working CRTs will “work” up to about 50% with minor washout starting there and increasing

Your screen is either cheap or worn, sometimes you had to increase the drive voltage on tired screens in the back and tolerate washout to get the screen useable , visible retrace is usually a give away if your screen is overdriven.

I always figured every crt is a unicorn and set the brightness and contrast each time until it was the most pleasant and readable, occasionally had to tolerate low contrast with a bit of washout, loosing focus is another issue that sometimes can be addressed in the back

Reply 12 of 37, by vorob

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Okay, whole day I was running videos to make screen working. Still greenish 🙁 Only setting green down to 70-80% fix the issue. Sad…

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Reply 14 of 37, by Boohyaka

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I've had a Sony Trinitron with an obvious green tint, which looks pretty similar to the kind of issue you're having, and I've been lucky to have someone point me to hardforum.com post sharing the software and tutorial to restore it to its former glory using a simple USB to TTL adapter and a software called WinDAS. Fully story there: Sony Multiscan CPD-G500 backlight/green tint issue where you will find the hardforum link if you want to read it all.

So the issue is "G2 Voltage" and I've been able to tune it down to restore the screen to perfect black. No more green bias!

Your screen definitely has a special service mode accessible through a specific connector and software as well - see page 13 of the service manual: https://www.manualslib.com/download/781240/Lg … tron-F700p.html but there's not a lot of specific information on what is needed, and I have absolutely no idea if WinDAS is specific to Sony Trinitron only or if there's hope to make it work on other brands like yours.

In any case, finding the interface and software mentioned in the service manual may be worth some effort, as section 5 "white balance and luminance" mentions controls like R-BIAS/G-BIAS/B-BIAS that sound interesting to fix your problem.
I really am not sure how relevant or useful this information may be. There are some knowledgeable peeps on that board, so maybe it is worth sending a message in a bottle in reply to the topic, or create a new one?

As a CRT lover and dedicated preservationist, I find so sad that the knowledge and tools to service CRT screens is slowly dying. Hope you manage to fix yours, good luck

Reply 15 of 37, by imi

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vorob wrote on 2022-07-20, 14:20:

Okay, whole day I was running videos to make screen working. Still greenish 🙁 Only setting green down to 70-80% fix the issue. Sad…

am I missing something here? ^^
it's fixed, why sad?

no need to fiddle with internal voltages when the external controls still have enough range to fix it, use it and have fun 😀

CRTs getting worn out is just normal, and you'll have to adjust settings over time, as long as it looks good to you afterwards that's all that matters.

Reply 16 of 37, by snufkin

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If I'm reading right, then I think it's a bit odd that the colours are ok in Windows but not the game. Or if you correct the monitor for the game then it's wrong in Windows. Maybe there's some colour change at different resolution/frequency?

Reply 17 of 37, by vorob

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My mistake. Colours in Windows and other games are also greenish. But in Thief it’s more obvious. Maybe when there is a dark scene on screen green is more aggressive, I dunno. Because in bright games greenish don’t bother me that much.

Reply 18 of 37, by TheMobRules

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Regarding brightness, I usually set it this way: I display a fully black screen, and set contrast and brightness to 0%. At that point the screen should be completely black. Then I turn brightness up until the point where it becomes dark gray (you may need to do this in a dark room) and then back down a notch until it's fully black again. You want that point where the screen is still completely black but turning it up even just a bit would make the dark grey hue appear. After that, I display a black and white image and I set contrast so that it looks good. There was a guide somewhere with these instructions but that's about it.

As for the green tint, have you tried to get the user color back to the factory default settings for the resolution you're using on that game? Unfortunately when you get a used CRT you usually don't know if someone fiddled with the internal pots (G2, RGB bias and such) or if it's been used so much that some parts have just worn out, but as mentioned above, if you can still get a pleasing image by using only the external controls you should be good.

Reply 19 of 37, by mkarcher

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vorob wrote on 2022-07-20, 12:45:

Guys, what’s the story behind brightness slider on CRT monitors? From what I see it doesn’t change the bright areas but it makes black look grey and that’s it.

That's an unusual, but possible implementation of brightness. Typically I expect that it should make both dark and bright areas brighter. You should set it in a way that black is black, but dark gray is visibly different from black. If your computer supports it, try to visit http://www.lagom.nl/lcd-test/contrast.php (it is called LCD-Test, but the color gradients are equally helpful for setting brightness and contrast on CRT monitors). You can compare it to the display on a properly set digital LCD monitor for reference.