ziggy587 wrote on 2023-05-07, 19:26:

When I say the picture is too dark, I mean that on the default brightness setting the screen is way too dark to use. Turning the brightness up, even all the way up, still doesn't make it bright enough. And as a result of turning the brightness up, the picture gets blown out (text is blurry and unreadable).

This means that likely the picture tube is worn out. You can try to adjust the G2 voltage, which controls a base brightness level. Adjusting the G2 voltage is usually done by turning a knob on the flyback transformer. This might give the CRT some extra useful life. Recapping the monitor is not going to help with this issue.

worn out 17", recycle and look for 20-21 inch CRT locally

mkarcher wrote on 2023-05-07, 21:07:

ziggy587 wrote on 2023-05-07, 19:26:

When I say the picture is too dark, I mean that on the default brightness setting the screen is way too dark to use. Turning the brightness up, even all the way up, still doesn't make it bright enough. And as a result of turning the brightness up, the picture gets blown out (text is blurry and unreadable).

This means that likely the picture tube is worn out. You can try to adjust the G2 voltage, which controls a base brightness level. Adjusting the G2 voltage is usually done by turning a knob on the flyback transformer. This might give the CRT some extra useful life. Recapping the monitor is not going to help with this issue.

Thanks for the info. I did a Google image search for CRT flyback transformer and found that most have two trim pots labeled "focus" and "screen." Would "screen" be the G2 voltage?

Let me ask you this: I'm assuming I'll be increasing the voltage to brighten the screen. So let's say this fix works to a desirable degree. Would I expect to see the screen darken again over time? I would guess yes. But how soon? Weeks, months, years? I'm just trying to gauge if it's worth it.

Sounds like an easy enough fix, if it's just adjusting a trim pot. I have to admit, I'm kind of a wuss about poking around inside a CRT. I'm assuming it would be best to do this while it's powered on, so I can see the picture while making the adjustment.

But I think first I should see if the scratches can be hidden, otherwise everything else is moot.

rasz_pl wrote on 2023-05-08, 06:06:

worn out 17", recycle and look for 20-21 inch CRT locally

Advice taken. I am wondering if it's worth my time or not. But as for finding a CRT locally, that's not easy here. Places are either picked clean, or extremely overpriced. The identical Dell monitor that I mentioned, I only have it because of luck. I happened to find it on the side of the road while at a red light and had my passenger hop out and grab it 🤣.

Adjusting the brightness via the flyback may work ok-ish but don't expect it to have really good contrast afterwards.

I used that adjustment back in the day when CRTs were still the main type of monitor and on some it worked ok but on others, it either made a certain color take over, usually green or it washed out the picture.

It could also be the symptom of incorrect voltage in the first place from a voltage regulator being bad or even just from bad solder joints.

ziggy587 wrote on 2023-05-09, 00:33:

Thanks for the info. I did a Google image search for CRT flyback transformer and found that most have two trim pots labeled "focus" and "screen." Would "screen" be the G2 voltage?

Exactly. "Screen" and "G2" are two different names for the same electrode in the CRT. The name "screen" at this point is not related to the display device as whole, but to the function of that grid: It screens unwanted electons from hitting the phosphor. It's a kind of throttle.

ziggy587 wrote on 2023-05-09, 00:33:

Let me ask you this: I'm assuming I'll be increasing the voltage to brighten the screen. So let's say this fix works to a desirable degree. Would I expect to see the screen darken again over time? I would guess yes. But how soon? Weeks, months, years? I'm just trying to gauge if it's worth it.

Actually, you are descreasing the screening effect to get a brighter picture. This doesn't fix the core problem you are observing: The electron source (the cathode) isn't able to source electrons as well as it is supposed to, but you make better use of the electrons it is still able to source. There might be a secondary effect of loosing focus when you adjust G2/screen, which can partially be compensated by adjusting focus, too. I can't tell you offhand how long it works on your screen, but getting 1000 hours more of operation with a usable brightness and focus trade-off is likely.

ziggy587 wrote on 2023-05-09, 00:33:

Sounds like an easy enough fix, if it's just adjusting a trim pot. I have to admit, I'm kind of a wuss about poking around inside a CRT. I'm assuming it would be best to do this while it's powered on, so I can see the picture while making the adjustment.

Yes, you should do this adjustment with the power turned on. Make sure you dont touch anything. Prefer an insulated screw driver. Test whether your tool fits the knob while the CRT is still powered off. Best to have a second person around in case something does go wrong. The recovery plan when you got an electric shock (quite unlikely if you work carefully, TV technicians do this all the time and don't get shocked) is to cut the power, and if you show health issue, call emergency rescue.

Awesome. Thanks for the info, guys! I always learn so much when I post questions here.

I can definitely check for bad solder joints, that's not too hard. And I do have a set of insulated drivers, rated up to 1000 volts IIRC. But I think the elephant in the room is the scratches on the screen. If I can't make them go away (at least be hardly noticeable) then fixing the dark screen is pretty much pointless. I suppose it's also the easiest starting point since I don't even have to open it up.

I've thought of a third option. Since I have an identical model monitor that is Dell branded, if I decide to trash this IBM monitor I could simply keep the front bezel. That would allow me to swap the bezels, depending if I wanna set up my IBM or Dell machine.

Hmm, and now I'm just thinking... If either or both problems aren't fixable, would it be worth keeping anyway for spare parts for my Dell monitor?

You are from NY, latte is $10, minimum wage is $15. This is a waste of your time, bin it and find another one using local classifieds. Post your own CRT wanted ad on FB or something, visit local hackerspace etc. Anything is more productive than trying to revive 20 year old smashed CRT 😀

rasz_pl wrote on 2023-05-10, 04:40:

Anything is more productive than trying to revive 20 year old smashed CRT 😀

Except if the goal is to get some experience in tuning worn-out CRT devices. You never know what people enjoy in the Retro Hobby. Is it playing old games? Is it getting a good rig? Is it fiddling with the stuff? Is it fixing stuff?

From the first post it seems the goal was acquiring working CRT monitor 😀 There are almost 20 hackerspaces in NY if OP want hands on electronics learning/workshop https://wiki.hackerspaces.org/New_York_City. Those are also excellent places to ask about spare CRTs for sale locally with no shipping involved.
All Im saying is learning about buffing glass to get rid of scratch is not the most optimal resource allocation strategy in a place with $3K rents.