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giobbi
May 27th, 2014, 01:52 PM
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

Stone
May 27th, 2014, 01:59 PM
Briefly:

1) That's a 'feature' of the 5151. :-)

2) Another 'feature'.

3) The only fix for 'screen burn' is another CRT.

SpidersWeb
May 27th, 2014, 02:22 PM
Yeah the IBM 5151 was targeted for office use - so it's designed to be sharp and easy on the eyes.

mikey99
May 27th, 2014, 02:23 PM
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.

vwestlife
May 27th, 2014, 02:26 PM
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.

giobbi
May 27th, 2014, 02:39 PM
ok, many thanks to you all, at least I know I can stop trying and hoping ;-)
cheers,
Giovi

KC9UDX
May 27th, 2014, 03:17 PM
"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.

vwestlife
May 27th, 2014, 04:50 PM
"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.

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.

giobbi
May 27th, 2014, 04:58 PM
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?" ;-) )

offensive_Jerk
May 27th, 2014, 09:36 PM
; 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.

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

Chuck(G)
May 27th, 2014, 09:50 PM
...and now you understand the real reason that screen savers were developed. :)

Ole Juul
May 28th, 2014, 12:47 AM
. . . at least I know I can stop trying and hoping ;-)

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.

deathshadow
May 28th, 2014, 01:11 AM
The question is: why IBM decided for a so looooong-persistance model? (of course the final answer will be "booooh?" ;-) )
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.

Malc
May 28th, 2014, 01:15 AM
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.

Stone
May 28th, 2014, 02:19 AM
If anybody's looking for a gem:

http://www.vintage-computer.com/vcforum/showthread.php?38382-IBM-5151-mono-monitor-in-excellent-condition

giobbi
May 28th, 2014, 08:58 AM
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. :)


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



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.


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.



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.

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 ;-) )

KC9UDX
May 28th, 2014, 09:52 AM
Sounds to me like the solution to your "problem" is a new CRT of a different part number.

SomeGuy
May 28th, 2014, 10:06 AM
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 :)

luvit
May 28th, 2014, 03:22 PM
giobbi, does it look much different than this? (pic is not my 5151)
can you post a pic?
http://kicken.dendmedia.com/ibm_windows_1.jpg

Stone
May 28th, 2014, 03:32 PM
If that pic is truly representative of how the monitor actually appears it's probably due for a flyback.

luvit
May 28th, 2014, 03:37 PM
stone, i chose a pic that represents the size of the actual display dimensions.
however, my first thoughts on that pic were another guy that doesn't understand how to turn his contrast and brightness knobs.

Stone
May 28th, 2014, 03:57 PM
It still looks out of spec -- I doubt any amount of adjustment would make it look very good.

vwestlife
May 28th, 2014, 04:57 PM
It still looks out of spec -- I doubt any amount of adjustment would make it look very good.

The display is overexposed because the CRT was too bright for the camera, so that's why it looks blown-out.

SpidersWeb
May 28th, 2014, 05:25 PM
I've noticed that with my 5151's - for my iPhone or video camera I have to turn the brightness down quite a way to get them to take an accurate photo. Don't have that issue with other CRTs.

KC9UDX
May 28th, 2014, 05:31 PM
I've noticed that with my 5151's - for my iPhone or video camera I have to turn the brightness down quite a way to get them to take an accurate photo. Don't have that issue with other CRTs.

It may well be the phosphor persistence that causes that. I don't know much about digital cameras, but I think they mostly use very long aperture times.

I'll have to look. I have some pictures of a long-persistence monitor in the same picture as my PET. Maybe there's a difference.

This is not the picture I was looking for, but the long-persistence CRT in the upper left looks overexposed compared to the other two, which are short-persistence. However, it may be an illusion due to the image displayed.
18875

KC9UDX
May 28th, 2014, 05:41 PM
On second thought, here's another view of the same scene. The brightest levels on the top left monitor really should be pretty close to the same as the other two monitors, yet they appear white, which clearly is overexposure. For that 'phosphor' to appear white would be disastrous!
18876

giobbi
May 29th, 2014, 11:54 AM
giobbi, does it look much different than this? (pic is not my 5151)
can you post a pic?


Ok here you have a couple of pics of mine:

18890 18891

To be honest, the image size doesn't seem so different from the picture you posted...

And here there's a clip about the long-persistance effect (I hope it's clear):

https://www.youtube.com/watch?v=0ZKdSpv2EU0&feature=youtu.be

cheers,
Giovi

Ole Juul
May 29th, 2014, 01:26 PM
Ok here you have a couple of pics of mine:

18890 18891

To be honest, the image size doesn't seem so different from the picture you posted...

And here there's a clip about the long-persistance effect (I hope it's clear):

https://www.youtube.com/watch?v=0ZKdSpv2EU0&feature=youtu.be



That looks just fine in the pics, and the persistence in the video seems normal - exactly what you'd expect for P39. I must admit that I don't understand for the life of me what you're on about. Perhaps I'm missing something here. Is that game designed for this monitor?

vwestlife
May 29th, 2014, 01:32 PM
Ok here you have a couple of pics of mine:

That looks like CGA emulation mode, which may not use the entire area of the display, due to the difference in resolution between CGA and MDA/Hercules.

offensive_Jerk
May 29th, 2014, 01:36 PM
https://www.youtube.com/watch?v=0ZKdSpv2EU0&feature=youtu.be

Giovi
that's not that bad...Try playing PacGal on the 5151. Now that's a challenge.

KC9UDX
May 29th, 2014, 01:50 PM
There's a potentiometer on the bottom of the PCB, with an access hole on the bottom of the monitor. R53 Persistence. :rolleyes:

luvit
May 29th, 2014, 02:42 PM
That looks like CGA emulation mode, which may not use the entire area of the display, due to the difference in resolution between CGA and MDA/Hercules.
yeah, i couldn't put my finger on it before I read your post. I think you're right, of course.
for clarity, giobbi, that explains the burn-in of the border not lining-up with your text.

giobbi
May 29th, 2014, 07:00 PM
Ok, ok, it seems I'm expecting too much from this old boy ;-)



There's a potentiometer on the bottom of the PCB, with an access hole on the bottom of the monitor. R53 Persistence. :rolleyes:


No hole on my monitor, maybe you're referring to a different revision...? (mine is labeled 5151200).

I found the width control (why, oh why I didn't see it before?????), so I got a larger image. But the height of the image remains a little smaller than its previous size (comparing with the burnt image). Here you have a couple of pictures with the board and some explanations (and some doubts) about pots/coils.

The dynamic focus coil is broken and the nucleus felt in pieces off of it; actually I got some image stabilization issues in the first seconds of use (I didn't tested extensively it yet). I tried to put some pieces back into the coil, but I don't know yet if it worked. I will see later.

18897

18898

A question: how does the the pot height work? The more resistance, the higher image, or vice versa? I'm wondering if the pot changed its nominal value, due to its age...?

I'm going to look for some schematics about the CRT board; if you have any link, it would be appreciated! :-)

cheers,
Giovi

Ole Juul
May 29th, 2014, 07:28 PM
Ok, ok, it seems I'm expecting too much from this old boy ;-)

With all due respect, I don't think you're expecting too much, but rather the wrong thing. :)



I'm going to look for some schematics about the CRT board; if you have any link, it would be appreciated! :-)

One of our members, minuszerodegrees (http://www.minuszerodegrees.net/), very kindly keeps this stuff on file for the world to use. Here's the manual for the 5151 (http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCoQFjAA&url=http%3A%2F%2Fwww.minuszerodegrees.net%2Foa%2FO A%2520-%2520IBM%2520Monochrome%2520Display%2520(5151).pdf&ei=cvmHU93-IdOkyASp9oLoDg&usg=AFQjCNE4azIPGu0QRvJseP-P13dNUX1X1A&bvm=bv.67720277,d.aWw).

KC9UDX
May 30th, 2014, 05:10 AM
Ok, ok, it seems I'm expecting too much from this old boy ;-)

Sorry, it was a bad joke. There's no persistence control.

giobbi
May 30th, 2014, 10:33 AM
Sorry, it was a bad joke. There's no persistence control.

Grrrrr, I opened (again!) the CRT hoping to find an hidden pot I didn't see before! Nice joke, it worked, I believed you! :D

giobbi
May 30th, 2014, 10:36 AM
With all due respect, I don't think you're expecting too much, but rather the wrong thing. :)

yes, you're right on that. :-)



One of our members, minuszerodegrees (http://www.minuszerodegrees.net/), very kindly keeps this stuff on file for the world to use. Here's the manual for the 5151 (http://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CCoQFjAA&url=http%3A%2F%2Fwww.minuszerodegrees.net%2Foa%2FO A%2520-%2520IBM%2520Monochrome%2520Display%2520(5151).pdf&ei=cvmHU93-IdOkyASp9oLoDg&usg=AFQjCNE4azIPGu0QRvJseP-P13dNUX1X1A&bvm=bv.67720277,d.aWw).

Got it, thank you!

cheers,
Giovi