5151 high-persistence phosphor ghosting

[Ken Vaughn]

I acquired an old IBM 5151 green phosphor monochrome monitor. It works fine, but the ghosting is more pronounced than I remember from the early 80's. When I scroll the display, the image persists for much longer than I think is normal -- it takes around 2 seconds to completely decay.

Is this evidence of some hardware problem? Does the phosphor change over time and become more persistent? Changing the brightness and contrast doesn't change the ghosting.

 

[mikey99]

This certainly brings back some memories In the early 80's I worked in a lab where we did all types of measurements on CRT displays.
I built a 'persistence meter' from a kit, that allowed us to measure phosphor persistence and decay time on various CRTs.

I recall the 5151 phosphor did have a long persistence. I don't currently own a 5151 so I can't say if this is normal but maybe someone
else that owns a 5151 will do a comparison.

 

[Druid6900]

I believe that the phosphors back then were quite slow to decay. I have I believe it's a Tandy VM-1 monitor that the sold with the Tandy 1200 (I have the 1200 too, but, I'm waiting for the parts to crawl back together) and they had a deadly case of persistence going on. A couple of seconds was about right.

I recall that the amber monitors had the same problem at the time.

 

[MikeS]

In my experience the 5151 really did have unusually long persistence, one of the things that struck me when I saw my first IBM PC.

 

[glitch]

Yes, the 5151 was especially slow! Mine would continue to glow even if it wasn't on -- the lighting in the workshop was enough to charge the phosphor, and if you shut the lights off or blew a fuse (it was a basement workshop, no windows) you could clearly see the 5151 glowing faintly.

 

[Ole Juul]

Yes, the 5151 was especially slow! Mine would continue to glow even if it wasn't on -- the lighting in the workshop was enough to charge the phosphor, and if you shut the lights off or blew a fuse (it was a basement workshop, no windows) you could clearly see the 5151 glowing faintly.

Indeed, I remember them as being the slowest. A little Google and I see the 5151 used the P1 phosphor like in oscilloscopes. (Some info here) I prefer the green and other green ones I've used were not as slow and nor were the amber ones.

I still think the 5151 is the best monitor ever made, particularly because of their choice of phosphor. I like to make use of the afterglow in creating images. For text it is nice that if just smoothly fades from one screen to the next - very easy on the eyes compared to modern screens where you have to fake all those effects which were native to the 5151.

 

[Shadow Lord]

I can confirm that indeed the refresh is on the order of seconds. I have what is essentially NIB 5151 and it exhibits the same slow decay. Definitely don't remember it being that bad w/ my Goldstar Amber Monitor.

 

[barythrin]

Ooh...oooh.. time for my ignorant question! Does phosphorus have any sort of decay over time or use? I know that's mostly radioactive terms but just like testing a radioactive tuning chip which has X element on it and a date you would calculate the decay over the date to figure out if your meter is tuned right. Not sure if anything like that would exist for phosphorus.

 

[Chuck(G)]

Ooh...oooh.. time for my ignorant question! Does phosphorus have any sort of decay over time or use? I know that's mostly radioactive terms but just like testing a radioactive tuning chip which has X element on it and a date you would calculate the decay over the date to figure out if your meter is tuned right. Not sure if anything like that would exist for phosphorus.

'Scuse me?

Phosphorous-31 is the only naturally-occurring isotope and is stable. There are other radioactive isotopes, but none with a half-life of more than a couple of weeks.

Phsphors have nothing to do with phosphorous. The similarly in names is because of the Geek stem for "light". The "white" allotrope of elemental phosphorous reacts with oxygen and glows as it oxidizes. However white phosphorous is luminescent in the presence of oxygen.

A phosphor, on the other hand, is something that produces light when excited. Excitation can be from light (of a different frequency) or electrons or X-rays. Phosphors used in CRTs generally do not contain phosphorous.
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I couldn't stand the persistence of the 5151 screen. I replaced mine with a third-party medium-persistence amber phosphor unit.

 

[glitch]

AFAIK it doesn't break down "just sitting there" like radioactive elements decay, but it definitely becomes dimmer as the tube is used for a long time. I replaced the original tube in my Heathkit OL-1 oscilloscope for this reason.

I never understood IBM's choice of such a high-persistance phosphor for the 5151. The NEC APC I've got with color screen is also pretty high-persistance. I think the amount of persistance found in the Kaypro II's monitor or the Heath/Zenith H-19 terminal is perfect, and the green-on-black is very easy to read.