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IBM 5151 monochrome (green) monitor issues

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.
 
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.
 
SpidersWeb said:
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.
Click to expand...

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.
Persistence.jpg
 
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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!
Pers2.jpg
 
giobbi said:
Ok here you have a couple of pics of mine:

View attachment 18890 View attachment 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
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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?
 
There's a potentiometer on the bottom of the PCB, with an access hole on the bottom of the monitor. R53 Persistence. :rolleyes:
 
vwestlife said:
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.
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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.
 
Ok, ok, it seems I'm expecting too much from this old boy ;-)


KC9UDX said:
There's a potentiometer on the bottom of the PCB, with an access hole on the bottom of the monitor. R53 Persistence. :rolleyes:
Click to expand...


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.

Potenziometri monitor spiegati.jpg

CRT board.jpg

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
 
giobbi said:
Ok, ok, it seems I'm expecting too much from this old boy ;-)
Click to expand...

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! :)
Click to expand...

One of our members, minuszerodegrees, very kindly keeps this stuff on file for the world to use. Here's the manual for the 5151.
 
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