Curious why you are using a CRT based monitor ? Are you running a CGA or EGA card ? I have a few old CRT that I use for testing EGA cards and the like but use newer LCD/LED type for everyday use including testing and general use, don't want one of the old CRT's to die because I use it every day. A decent older 4:3 LCD can be found for very cheap to emulate an old CRT type for daily use. Just my opinion...

It sounds like blooming, this phenomenon happens on most shadow mask CRTs and is absolutely normal.

What happens is that whenever a bright image is displayed, the mask "expands", on some tubes it isn't noticeable on others it is.

@Horun
You seem to be forgetting that most if not all 4:3 LCDs have a crappy upscaler (although some have better upscaler than others) that will turn the image into a smeary, unreadable and blurry mess of pixels, and by design, LCDs must upscale everything to their native resolution.

Horun wrote:

Curious why you are using a CRT based monitor ? Are you running a CGA or EGA card ? I have a few old CRT that I use for testing EGA cards and the like but use newer LCD/LED type for everyday use including testing and general use, don't want one of the old CRT's to die because I use it every day. A decent older 4:3 LCD can be found for very cheap to emulate an old CRT type for daily use. Just my opinion...

Apart from nostalgia there are good reasons to use a CRT, specifically an old fuzzy shadow-mask CRT with retro stuff. DOS games were designed around those screens, the designers assumed edges wouldn't be completely sharp and there might be a bit of bleeding. Take 320x240 and upscale to TFT resolutions and you get big, nasty, sharp blocks. Even on a Trinitron/Diamondtron CRT it's arguable that a lot of old DOS VGA output looks 'wrong', too clinical, let alone on a TFT.

But aside from this hypothesizing, OP, exactly which monitor are we talking about here? Most PB screens were Tatung (TGMN.... model number) or Hyundai (HNMN...) models. Decent-ish shadow mask, nothing special but not awful. But "most" isn't all, so exact identification could help.

Vynix wrote:

It sounds like blooming, this phenomenon happens on most shadow mask CRTs and is absolutely normal. […]
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It sounds like blooming, this phenomenon happens on most shadow mask CRTs and is absolutely normal.

What happens is that whenever a bright image is displayed, the mask "expands", on some tubes it isn't noticeable on others it is.

@Horun
You seem to be forgetting that most if not all 4:3 LCDs have a crappy upscaler (although some have better upscaler than others) that will turn the image into a smeary, unreadable and blurry mess of pixels, and by design, LCDs must upscale everything to their native resolution.

I've seen blooming (when opening a file explorer or primarily white window in Windows, for example), however, this is a constant jitter back and forth. It happens a couple of times a second or so, almost like the edges are vibrating. I wish this was blooming, but something tells me this isn't.

dionb wrote:

Apart from nostalgia there are good reasons to use a CRT, specifically an old fuzzy shadow-mask CRT with retro stuff. DOS games were designed around those screens, the designers assumed edges wouldn't be completely sharp and there might be a bit of bleeding. Take 320x240 and upscale to TFT resolutions and you get big, nasty, sharp blocks. Even on a Trinitron/Diamondtron CRT it's arguable that a lot of old DOS VGA output looks 'wrong', too clinical, let alone on a TFT.

But aside from this hypothesizing, OP, exactly which monitor are we talking about here? Most PB screens were Tatung (TGMN.... model number) or Hyundai (HNMN...) models. Decent-ish shadow mask, nothing special but not awful. But "most" isn't all, so exact identification could help.

That's a big reason why I use the CRTs instead of LCDs- and that's also why I'm so worried about this, is because I don't believe I have any other shadow mask CRTs. The image this one produces is very distinct from the others, and looks much better for DOS/DOS games.

As far as the model number goes:

If you don't have any 50/60Hz transformer nearby the rear of the monitor (they create a changing magnetic field that could cause such a jitter) there's likely some electronics problem in it and if capacitor change is as good as dead, all other things involving testing and swapping stuff in it are aswell.

Tiido wrote:

If you don't have any 50/60Hz transformer nearby the rear of the monitor (they create a changing magnetic field that could cause such a jitter) there's likely some electronics problem in it and if capacitor change is as good as dead, all other things involving testing and swapping stuff in it are aswell.

I mean, I recently disassembled an old APS battery backup thing with no battery in it to clean it and use it as a glorified power strip, however, the transformer both is disconnected from any power source and is at the moment just a heavy-ish small brick of metal, and is several feet away on the floor. I could try taking it out of the room entirely when I get home, though I doubt it's the cause as it's so far away both horizontally and vertically, and the fact that it's off. I am unaware if those generate any magnetism when they're off, though I don't believe they do.

Horun wrote:

Curious why you are using a CRT based monitor ? Are you running a CGA or EGA card ? I have a few old CRT that I use for testing EGA cards and the like but use newer LCD/LED type for everyday use including testing and general use, don't want one of the old CRT's to die because I use it every day. A decent older 4:3 LCD can be found for very cheap to emulate an old CRT type for daily use. Just my opinion...

Personally, I am very purist in that sense. I like to keep things as close to how they originally would've been used as possible. In my mind, that way of thinking is very dangerous- it can start with the active use of LCDs to preserve the CRTs themselves, but I feel like that could eventually degenerate into other, far more aggressive drop-offs: the use of DOSBOX and similar emulators, to well, emulate the functionality of an old computer gaming-wise to prevent wear on the original equipment itself, or the use of things like PCem to experience the operating systems themselves without risking the original hardware.

I was stuck with things like VirtualBox, DOSBOX, Virtual PC 2007, and PCem for years. After that, I was stuck with only LCDs to drive my, at the time, very small and weak vintage PC collection. The first time I was able to get a CRT, I was thrilled- a huge 19" ~50lb monstrosity from 2001, that was still crisp, and worked (hopefully, still works) great. The last thing I want to do now is start to rewind on the progress I've made, and begin using LCDs again. That is just how I've been since I've been able to get more and better vintage hardware over time. That's really why I so aggressively refuse to use things like LCDs.

athlon-power wrote:

the horizontal edges of the screen move back and forth a couple of millimeters or so, but the center stays solid. The top and bottom edges of the drawn screen also stay still; it's only the horizontal edges of the drawn image.

I don't get it, does raster stretch out vertically or horizontally? What have you tried to remedy the issue so far? Better post a video of the fault.

SSTV2 wrote:

I don't get it, does raster stretch out vertically or horizontally? What have you tried to remedy the issue so far? Better post a video of the fault.

I left it for about 8 hours while I went to college. It was off and unplugged from the wall the whole time. It appears to be quite minimal now, still there, but minute enough to where I can't easily record it. I'll see if it gets worse the longer it is on.

It seems that this was caused by a set of magnetic screwdrivers I was storing somewhat nearby (approx. 1.5ft away from the monitor) in a little plastic organizer. The fact that they could cause something like that never even occurred to me, and bringing them far away (now approx. 10-12ft away, with the walls and doors of a closet separating the two) seemed to reduce it quite a bit, but not all the way.

I suspect that I need to leave the monitor unplugged and sitting away from anything that could even possibly be magnetic for a few days, and return to it and see if anything has improved. I brought my other 15" CRT, a Gateway EV500, here, and it's been working just fine.

One thing I think is also part of the problem is that the PB CRT is "dumb," so to speak. It has almost zero signs of any digital controls- there are no buttons, only dials located at the bottom of the monitor. Even the pincushion is changed via a phillips screw on the back of the unit, which is actually when the idea of those screws being magnetic hit me. I hadn't even thought of it until I was fiddling with the pincushion to see if it would reduce the jitter, and the tip accidentally touched the screen, causing the famous purple/greenish effect. I immediately took all the magnetic screws, and threw them into their organizer, and up into the farthest corner away from the CRT I could find in the closet. Anyways, there's no degauss, nothing. There is nothing digital in it at all, everything seems to be as analog as it gets. I theorize this is why the magnetic screwdrivers bother this CRT, when I had similar screwdrivers on top and beside of my old Hyundai CRT with little to no effect- the computer in it somehow manages the extra (but quite weak) magnetic fields, either that, or it degaussed itself every time it turned on, never allowing me to notice any ill effects.

With the screwdrivers the same distance away (this was before I had thought of them) the Gateway ran just fine, everything was solid and looked great. The Gateway monitor also has digital controls, and an OSD you can pull up, just like the Hyundai. I wonder if anybody has thought of doing some testing between "dumb," and "smart," CRT monitors, and their resilience to things such as that. I definitely am not going to do that and risk any of my CRTs, and from now on, I'm going to double-check as to whether I have magnetic things around my retro setups. Even if the PB really is dead, and it had nothing to do with those screwdrivers, which I now doubt a fair bit, I at least learned a lesson with making sure my setups don't get screwed up by simple mistakes like this, no pun intended.

Better monitors have magnetic shielding cage around the tube so that they are much less sensitive to external fields. Neck area is the most sensitive part since small change there gets amplified dramatically by the deflection later on.
These screwdrivers shouldn't cause any sort of pulsations though, only some sort of static effect...

Says if you need to degauss the PB CRT, since it doesn't seem to have a degauss coil of its own, you could put another CRT of the same size, so it faces the PB's screen (make sure the other CRT is as close as possible) then kick the degauss on the 2nd CRT, this should degauss both CRTs in one go.

Tiido wrote:

Better monitors have magnetic shielding cage around the tube so that they are much less sensitive to external fields. Neck area is the most sensitive part since small change there gets amplified dramatically by the deflection later on.
These screwdrivers shouldn't cause any sort of pulsations though, only some sort of static effect...

While cleaning the Gateway CRT, I did notice that there were metal plates just below the plastic, so that might be the shielding. I never noticed this on the PB CRT, so I'll have to look and see. The fact that the screwdrivers would cause static is weird, as the farther away they are, the less the image jitters, and the closer you bring them, the more it jitters.

Vynix wrote:

Says if you need to degauss the PB CRT, since it doesn't seem to have a degauss coil of its own, you could put another CRT of the same size, so it faces the PB's screen (make sure the other CRT is as close as possible) then kick the degauss on the 2nd CRT, this should degauss both CRTs in one go.

That would be the Gateway EV500. While the PB is a 14" and the Gateway is a 15", I suspect it will work just fine. Should they be touching screen-to-screen or have the Gateway's back facing the PB? I'm guessing it's screen to screen but I want to make sure.

Yep it's screen to screen. I've done that with a iMac G3 (15" IIRC) and my trusty ol' LG 702S (17") as long the monitors are close enough in size this should do it.