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IBM 5151 monochrome (green) monitor issues

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giobbi

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Joined
Dec 23, 2012
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987
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São Paulo country, Brazil
Hi all,

I'm trying to fix some annoying issues on this old monitor (5151002) I got from a friend. It was extensively used in a production line, so it shows the DOS program screen even when it's off (quite common for that kind of use: it was left with the same program page many hours every day, for many years...)

maybe the issues are due to the many hours of use, I'm not sure:

1) The worst issue: it has an annoying fade effect while refreshing the screen: if you send a "clear screen" command (or if you simply scroll the image) it took a while (a second or more) before the old image disappears. Is it a CRT issue, or something concerning the CRT controller board?

2) I can't zoom the screen to fit the CRT size; it's like to have a 9" screen (or less) in a 12" CRT... I tried to play with the pots inside the cover, and the image improved a little bit (bigger); but there's no way to fit the CRT size.

3) Of course the old program screenshot "carved" in the CRT is quite annoying; is there any way to recover that? I guess there's no chance to fix it, but maybe there's some program/technique/... that can help a little...

cheers,
Giovi
 
I also tried adjusting my 5151 to fill the screen but didn't improve it much.

The "fade effect" you're referring to is caused by the long 'persistence' of the green phosphor used
in the 5151 CRT. Color CRTs' used a very short persistence phosphor. Longer persistence phosphors
continue to emit light for a longer time period after the CRTs electron beam is turned off.

Many years ago I worked in a lab where we tested CRT displays. One of my projects was
to build a 'Persistence meter' that could be used to measure the persistence of various
CRT phosphors. The meters output was fed into an oscilloscope. The meter had a sensor on a
cable that was placed against the screen showing a display of characters (we typically used all capital H's).
The sensor was positioned to receive maximum signal from one area of the screen. This resulted in a
specific waveform on the oscilloscope. Then the display was changed to a blank screen and the
sensor responded to the fading of the phosphor. You could watch the waveform change and
take a measurement to indicate when the phosphor emission was completely gone.
 
The long-persistence phosphor helps to reduce eye strain, especially given the fact that the MDA/Hercules video standard only has a 50 Hz refresh rate, which would cause annoying flickering if used with short-persistence phosphor (such as what color monitors use).

IBM did make the 5151's phosphor a little too long-persistence, however, it is very similar (if not identical) to the kind of phosphor used on radar scopes and oscilliscopes, so it was probably the cheapest option.
 
"Too long" persistence "green screens"/"data displays"/"monochrome monitors" were quite common around that time, not something unique to IBM. In fact, I preferred them that way and I suspect others did too.
 
KC9UDX said:
"Too long" persistence "green screens"/"data displays"/"monochrome monitors" were quite common around that time, not something unique to IBM. In fact, I preferred them that way and I suspect others did too.
Click to expand...

IBM didn't have much choice at the time; either they could use the long-persistence P1 green radar scope phosphor, or the short-persistence P4 black & white TV phosphor, which would've been too flickery with the 50 Hz refresh rate. I don't think CRTs with medium-persistence P3 amber phosphor became common until 1983 or so; IBM did put an amber CRT into the 5155 Portable PC in 1984, although I think that's the only amber monochrome monitor they ever made, at least for the consumer market.
 
in the end of '70s / begging of '80s Commodore used a quite short-persistence green CRT in its PET line (CBM 30xx, 40xx, 80xx, etc.). The 40xx and 80xx line used a 11" CRT that are quite fast, if compared with the 5151 CRT... So it seems the short-persistence in green phosphor CRT was already available in that era; and the Commodore CRTs are quite good; IMO better than the IBM ones.
The question is: why IBM decided for a so looooong-persistance model? (of course the final answer will be "booooh?" ;-) )
 
vwestlife said:
; IBM did put an amber CRT into the 5155 Portable PC in 1984, although I think that's the only amber monochrome monitor they ever made, at least for the consumer market.
Click to expand...

I did wonder why they put an amber monitor in the Portable.

I had a post about the CRT boarder a while ago too. Hard to believe that the usable screen area is so small!
But, it sounds like your monitor is working perfectly except for the burn in. :D
 
giobbi said:
. . . at least I know I can stop trying and hoping ;-)
Click to expand...

Hoping? For what? To me the 5151 is the most beautiful screen ever. (I've got two of them) I see no practical reason why you would need to have a faster response. Like vwestlife said "The long-persistence phosphor helps to reduce eye strain". The monitor is intended for reading text, not watching videos. :)

Try to write some batch files to really take advantage of it. You can have beautiful streaks as things (try asterisks) disappear up the screen.

As for the size, I wonder if some voltage is low since it sounds like the size is smaller than it is supposed to be.
 
giobbi said:
The question is: why IBM decided for a so looooong-persistance model? (of course the final answer will be "booooh?" ;-) )
Click to expand...
Simple : 50hz refresh

As @vwestlife said...

The long decay phosphor meant there was less flickering at the low refresh rate, making it better for static content (like text) -- unlike color displays; it's why by the time of the VGA people started kvetching about 60hz in graphics modes 'flickering' and you started to see 85hz/higher. If you spent a LOT of time working with text, MDA (and by extension Hercules) beat the ever living tar out of CGA, or even EGA. It's also why 'page white' monochrome VGA (and other high res mono) had a brief surge of popularity with people who worked with "for print" layout as they too had a longer decay rate.

A problem today's LCD's avoid since they have (little to) no phosphor fade, and are a 'constant state' device.
 
I got 2 sad looking 5151's, Both have had a hard life, bruised battered and bad screen burn in, I don't use em just keep em for spares, I have an amber screen i use but i do prefer the 5151.
 
Ole Juul said:
Hoping? For what? To me the 5151 is the most beautiful screen ever. (I've got two of them) I see no practical reason why you would need to have a faster response. Like vwestlife said "The long-persistence phosphor helps to reduce eye strain". The monitor is intended for reading text, not watching videos. :)
Click to expand...

Yep, HD videos @ 1080p don't run well on my 5160/5151 system ;-)

Ole Juul said:
Try to write some batch files to really take advantage of it. You can have beautiful streaks as things (try asterisks) disappear up the screen.
Click to expand...

IMO the persistence is tooooo much, it takes *seconds* to fade out. I understand the anti-flickering effect inside, but it's too much, it's annoying.

Ole Juul said:
As for the size, I wonder if some voltage is low since it sounds like the size is smaller than it is supposed to be.
Click to expand...

I'm sure there's something wrong with it; the image borders don't reach the burnt section; it means (a long?) time ago the image was bigger. And, in every case, actually the image is smaller than the samples you can see on images.google.com.
Maybe some old caps? If you people have some advice, I could do some measurement and change what's wrong, but I will not put my hands in the high voltage section, I refuse to be bite again, once in a lifetime is enough (I was 10 years old and I still remember that episode ;-) )
 
Sounds to me like the solution to your "problem" is a new CRT of a different part number.
 
On the other hand, if it is already used and abused, you won't feel to guilty about leaving it on for long periods of time or getting additional burn in. Burn Nyan cat in to the screen :)
 
giobbi, does it look much different than this? (pic is not my 5151)
can you post a pic?
ibm_windows_1.jpg
 
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