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pcdata76
January 17th, 2016, 04:23 AM
Last week i picked up an IBM 5151 together with a clone XT computer. I'm new to pre-386 computers and their accessories and didnt used a 5151 monitor till now.

Monitor is functioning without problem, image is clear and crisp, but when i turned off the computer, monitor turns off with a very bright spot around the middle part of the screen. Is it normal for these monitors or something needs repair? (aged capacitors in monitor, or something bad on clone MDA card maybe?) In color monitors there is a circuit which turns the electron guns off just before turning the deflection off during power loss to prevent phosphor burn caused by bright spot at the middle of the screen, but i have no idea such a measure is built on these monitors too. Before starting to troubleshooting, i wanted to ask.

I recorded a video, http://vid1376.photobucket.com/albums/ah14/pcdata76/KARISIK/CAM00794_zps3gfn7lmu.mp4

Stone
January 17th, 2016, 04:43 AM
Older TVs do this, too.

bobba84
January 17th, 2016, 12:47 PM
My 5151 has always exhibited this same behaviour since I obtained it, and I've had it for 15+ years.

mikey99
January 17th, 2016, 03:05 PM
If you have the 5151 power cord plugged into the rear of the 5150 power supply.......turning off the 5150 power switch turns
off the 5150 and 5151 at the same time. Have you tried just unplugging the 5151 power cord to see if the symptoms are the same ?

retrogear
January 17th, 2016, 04:31 PM
Tried that with mine and it is an improvement. When I power off cpu and display at the same time, the display collapses to a bright line down the center. When I unplug the display first, it collapses to a one inch band
down the center then extinguishes so not as harsh. I don't see any phosphor burn so it does no damage anyway.

Larry G

T-R-A
January 17th, 2016, 04:46 PM
Here's a pretty good description of what's happening:

http://www.madsci.org/posts/archives/2000-09/970201922.Eg.r.html

retrogear
January 17th, 2016, 05:23 PM
Interesting, I had training on CRT's and the Sony Trinitron but had not heard of the use of an aluminum film to protect the phosphor.

Larry G

pcdata76
January 17th, 2016, 09:40 PM
Then it looks like this behaviour is by design and most probably won't harm the phosphor coating. My 5151 is 1984 made and should be powered off like that hundreds of times up to today. Anyway, i can make a short cable with a switch on it between computer and monitor to be able to turn off 5151 before shutting down the computer.

bobba84
January 18th, 2016, 01:10 PM
Tried that with mine and it is an improvement. When I power off cpu and display at the same time, the display collapses to a bright line down the center. When I unplug the display first, it collapses to a one inch band
down the center then extinguishes so not as harsh. I don't see any phosphor burn so it does no damage anyway.

Larry G

You're right, mine's the same. I'm very curious about the reason behind this. The beam raster is created in the circuitry of the monitor, not in the PC. Maybe it is easier for the raster to collapse without an input signal for some reason? Nevertheless, I'm going to pull the power on the 5151 first from now on. It seems kinder than the alternative.

retrogear
January 18th, 2016, 03:14 PM
The MDA display is unique because the horizontal and vertical drive to generate the raster from the pc IS the drive signal, not just for synchronization so when the PC is powered off, the H&V drive to deflect the beam is instantaneously gone but the
high voltage has not had time to bleed off so the beam continues to the center of the tube.

Larry G

bobba84
January 18th, 2016, 03:28 PM
The MDA display is unique because the horizontal and vertical drive to generate the raster from the pc IS the drive signal, not just for synchronization so when the PC is powered off, the H&V drive to deflect the beam is instantaneously gone but the
high voltage has not had time to bleed off so the beam continues to the center of the tube.

Larry G

That explains it. I believe it also explains why on cold boot the monitor doesn't make the static "ch" noise associated with power on until the PC starts sending a video image? Does that make sense? I've always wondered about that behaviour.

retrogear
January 18th, 2016, 03:37 PM
There is drive and high voltage as soon as the pc is powered on but you don't hear the static "crunch" sound on a monochrome display because HV is only around 10KV instead of approx. 20KV like a color display. More voltage, more static field.

Larry G

bobba84
January 18th, 2016, 04:09 PM
There is drive and high voltage as soon as the pc is powered on but you don't hear the static "crunch" sound on a monochrome display because HV is only around 10KV instead of approx. 20KV like a color display. More voltage, more static field.

Larry G

That makes sense. But mine definitely does a slight noise when the PC starts sending a signal.

retrogear
January 18th, 2016, 04:27 PM
>That makes sense. But mine definitely does a slight noise when the PC starts sending a signal.

You must have young ears :p

KC9UDX
January 18th, 2016, 04:55 PM
Then it looks like this behaviour is by design and most probably won't harm the phosphor coating. My 5151 is 1984 made and should be powered off like that hundreds of times up to today. Anyway, i can make a short cable with a switch on it between computer and monitor to be able to turn off 5151 before shutting down the computer.

It's not really by design, it's just a side-effect. It will harm the phosphor, eventually.

If you are worried about it (I wouldn't), the way to cure it is to apply a negative voltage to the control grid at power-down. That will eliminate it completely.

KC9UDX
January 18th, 2016, 04:58 PM
>That makes sense. But mine definitely does a slight noise when the PC starts sending a signal.

That's ultimately due to the sync circuits phase locking to the PC's output. You will hear "microphonics" from the sync and high voltage circuits, and you will hear a rapid change in static charge.

SquallStrife
January 18th, 2016, 05:38 PM
Then it looks like this behaviour is by design and most probably won't harm the phosphor coating. My 5151 is 1984 made and should be powered off like that hundreds of times up to today. Anyway, i can make a short cable with a switch on it between computer and monitor to be able to turn off 5151 before shutting down the computer.

Don't bother. It takes minutes of sustained illumination at normal brightness levels to "burn" the phosphors.

The few seconds your flash appears to exist for will have zero impact (remember these are long-persistence phosphors, they are only actually being illuminated for a fraction of a second, the majority of what you're seeing is the characteristic after-glow), and as we've seen in this thread, is simply a by-product of the monitor's design.

Storm in a teacup! :)

pcdata76
January 19th, 2016, 11:02 PM
That explains it. I believe it also explains why on cold boot the monitor doesn't make the static "ch" noise associated with power on until the PC starts sending a video image? Does that make sense? I've always wondered about that behaviour.

Yeah, there is no a separate free-running oscillator to generate HV and deflections as in modern monitors and TVs when there is no V/H sync signal to lock. That's why you don't see any raster or retrace lines when 5151 is powered on at maximum brightness with MDA cable disconnected. V/H sync signals from MDA adapter are needed to generate HV and deflections as Larry said.

nestor
January 21st, 2016, 11:16 AM
Don't bother. It takes minutes of sustained illumination at normal brightness levels to "burn" the phosphors.

Maybe not. I have just acquired a 5151 (the one I had died) and it has a severe phosphor burn in the middle-bottom of the screen.



https://lh3.googleusercontent.com/HWPTJh3hS-2vhRplxbTQRy6sAMIQ1EEjs6KRjnt2SPhVS3WO241iWlihfEQ-C56FumBLE52f9qrgvC1QEruZD2Eibrkt-CPb7hjD3Apwrb9e954LPX6fSY2vTmCw60Pi5HKQnZPrZQJ14Km 3aaSF69O7tDsAzg6Z3p2cv-sbOEid8pB3F17LdJC4UKVWb1CVkC5jpFTxRQT6jiyT6jrtA5ip 6bLJgoMcnPr02f-NlaPjx6U3gueEXTrgtWRhxveRxizFu0FRj38HshbD5iwZ-yJOEoNgx_-AJ3bum4m6x5ZJ_jJYv3XwmT6NNo-mu6DxkSaCNEEZf_jVWv3O6KW0I1F_BbHSWjIEfAVb6lHiQdzSW v_XTwAmhzLJltEfKbisDpeR0uUgO2IQEy_PElGVOg1ynzbpqjq IMjUbMf9MoQ8lfhjUC58v1RX--QMr3qJUT1GYx874AJZGkF_K-wQFOl6G1Mwy64LgOP5uiXHVGnCCowkWg0n7lZ85jg1hgzThWyM 0oMCbXRX-LesxJSfoqp2sptclhIZjpY7LS3y3XEDj54ZbNnQS6W0LsB50Sn kZwvaz=w640
Click to enlarge (https://lh3.googleusercontent.com/HWPTJh3hS-2vhRplxbTQRy6sAMIQ1EEjs6KRjnt2SPhVS3WO241iWlihfEQ-C56FumBLE52f9qrgvC1QEruZD2Eibrkt-CPb7hjD3Apwrb9e954LPX6fSY2vTmCw60Pi5HKQnZPrZQJ14Km 3aaSF69O7tDsAzg6Z3p2cv-sbOEid8pB3F17LdJC4UKVWb1CVkC5jpFTxRQT6jiyT6jrtA5ip 6bLJgoMcnPr02f-NlaPjx6U3gueEXTrgtWRhxveRxizFu0FRj38HshbD5iwZ-yJOEoNgx_-AJ3bum4m6x5ZJ_jJYv3XwmT6NNo-mu6DxkSaCNEEZf_jVWv3O6KW0I1F_BbHSWjIEfAVb6lHiQdzSW v_XTwAmhzLJltEfKbisDpeR0uUgO2IQEy_PElGVOg1ynzbpqjq IMjUbMf9MoQ8lfhjUC58v1RX--QMr3qJUT1GYx874AJZGkF_K-wQFOl6G1Mwy64LgOP5uiXHVGnCCowkWg0n7lZ85jg1hgzThWyM 0oMCbXRX-LesxJSfoqp2sptclhIZjpY7LS3y3XEDj54ZbNnQS6W0LsB50Sn kZwvaz=w1752-h985-no)

When I power off the 5160 with the 5151 connected to its power supply, it produces the same glow as the video in the first post. But when I connect the 5151 directly to the wall and power off the 5160, it produces a single line exactly in the same spot where the burn is.

https://lh3.googleusercontent.com/fL19JS3F0M01t7FPIfUrxCyUiDEiCqKV1nlDt6yBBVcG-w_q0sNPutLMYRdKOhCGx_uplpqXgp-2gBruNCtwQiR3pluApOkzhNNtKavtcedFpF9L_lXhnRjnixMIH P5iSfXgPz82iyCwdjjRhVMk8Kh2m3sw_HOLw9jlmt_bdLsUXA_ VTCE88zWCxYECzTbGjVXvd_MsfayTHHUrAyFMqFZOdeG263S8v EegI222kjVxHJaMSSMRi3dTHZEDUuGg8c3ERP9AejrZfARyLT0 06aHLeqYBPAHCPNSYXt4nhB8ihU7fEzDV2souNIsI0l56G3td4 hcoIA6g9PIBmKlub3lcWfZ9slsKC8Hl1eWFh1OmJjjKsyO7fKJ SHm-bvZmRjaImOCJIaI7x1U9e6RITWFWtOqPIr6w4JQ9e7PG04A1ft xG6hkko6GsEi_Pt_f2zCZMs38UMuWfBkkK6iQliJ9SK5PeeBWu Z03tqm7HoeIHAM9UYHjuVuwuWd-gWdMQ3p5is7xaciiAODWWC15OyigrYG-nvxGXkxVIXuczBW9CUvEipQqeU1M2VdLsQJwRUde-f=w640
Click to enarge (https://lh3.googleusercontent.com/fL19JS3F0M01t7FPIfUrxCyUiDEiCqKV1nlDt6yBBVcG-w_q0sNPutLMYRdKOhCGx_uplpqXgp-2gBruNCtwQiR3pluApOkzhNNtKavtcedFpF9L_lXhnRjnixMIH P5iSfXgPz82iyCwdjjRhVMk8Kh2m3sw_HOLw9jlmt_bdLsUXA_ VTCE88zWCxYECzTbGjVXvd_MsfayTHHUrAyFMqFZOdeG263S8v EegI222kjVxHJaMSSMRi3dTHZEDUuGg8c3ERP9AejrZfARyLT0 06aHLeqYBPAHCPNSYXt4nhB8ihU7fEzDV2souNIsI0l56G3td4 hcoIA6g9PIBmKlub3lcWfZ9slsKC8Hl1eWFh1OmJjjKsyO7fKJ SHm-bvZmRjaImOCJIaI7x1U9e6RITWFWtOqPIr6w4JQ9e7PG04A1ft xG6hkko6GsEi_Pt_f2zCZMs38UMuWfBkkK6iQliJ9SK5PeeBWu Z03tqm7HoeIHAM9UYHjuVuwuWd-gWdMQ3p5is7xaciiAODWWC15OyigrYG-nvxGXkxVIXuczBW9CUvEipQqeU1M2VdLsQJwRUde-f=w1752-h985-no)

So I would recommend connect the 5151 to the 5150/5160 power supply to avoid phospor burns.

pcdata76
January 21st, 2016, 11:27 AM
Maybe not. I have just acquired a 5151 (the one I had died) and it has a severe phosphor burn in the middle-bottom of the screen.



https://lh3.googleusercontent.com/HWPTJh3hS-2vhRplxbTQRy6sAMIQ1EEjs6KRjnt2SPhVS3WO241iWlihfEQ-C56FumBLE52f9qrgvC1QEruZD2Eibrkt-CPb7hjD3Apwrb9e954LPX6fSY2vTmCw60Pi5HKQnZPrZQJ14Km 3aaSF69O7tDsAzg6Z3p2cv-sbOEid8pB3F17LdJC4UKVWb1CVkC5jpFTxRQT6jiyT6jrtA5ip 6bLJgoMcnPr02f-NlaPjx6U3gueEXTrgtWRhxveRxizFu0FRj38HshbD5iwZ-yJOEoNgx_-AJ3bum4m6x5ZJ_jJYv3XwmT6NNo-mu6DxkSaCNEEZf_jVWv3O6KW0I1F_BbHSWjIEfAVb6lHiQdzSW v_XTwAmhzLJltEfKbisDpeR0uUgO2IQEy_PElGVOg1ynzbpqjq IMjUbMf9MoQ8lfhjUC58v1RX--QMr3qJUT1GYx874AJZGkF_K-wQFOl6G1Mwy64LgOP5uiXHVGnCCowkWg0n7lZ85jg1hgzThWyM 0oMCbXRX-LesxJSfoqp2sptclhIZjpY7LS3y3XEDj54ZbNnQS6W0LsB50Sn kZwvaz=w640
Click to enlarge (https://lh3.googleusercontent.com/HWPTJh3hS-2vhRplxbTQRy6sAMIQ1EEjs6KRjnt2SPhVS3WO241iWlihfEQ-C56FumBLE52f9qrgvC1QEruZD2Eibrkt-CPb7hjD3Apwrb9e954LPX6fSY2vTmCw60Pi5HKQnZPrZQJ14Km 3aaSF69O7tDsAzg6Z3p2cv-sbOEid8pB3F17LdJC4UKVWb1CVkC5jpFTxRQT6jiyT6jrtA5ip 6bLJgoMcnPr02f-NlaPjx6U3gueEXTrgtWRhxveRxizFu0FRj38HshbD5iwZ-yJOEoNgx_-AJ3bum4m6x5ZJ_jJYv3XwmT6NNo-mu6DxkSaCNEEZf_jVWv3O6KW0I1F_BbHSWjIEfAVb6lHiQdzSW v_XTwAmhzLJltEfKbisDpeR0uUgO2IQEy_PElGVOg1ynzbpqjq IMjUbMf9MoQ8lfhjUC58v1RX--QMr3qJUT1GYx874AJZGkF_K-wQFOl6G1Mwy64LgOP5uiXHVGnCCowkWg0n7lZ85jg1hgzThWyM 0oMCbXRX-LesxJSfoqp2sptclhIZjpY7LS3y3XEDj54ZbNnQS6W0LsB50Sn kZwvaz=w1752-h985-no)

When I power off the 5160 with the 5151 connected to its power supply, it produces the same glow as the video in the first post. But when I connect the 5151 directly to the wall and power off the 5160, it produces a single line exactly in the same spot where the burn is.

https://lh3.googleusercontent.com/fL19JS3F0M01t7FPIfUrxCyUiDEiCqKV1nlDt6yBBVcG-w_q0sNPutLMYRdKOhCGx_uplpqXgp-2gBruNCtwQiR3pluApOkzhNNtKavtcedFpF9L_lXhnRjnixMIH P5iSfXgPz82iyCwdjjRhVMk8Kh2m3sw_HOLw9jlmt_bdLsUXA_ VTCE88zWCxYECzTbGjVXvd_MsfayTHHUrAyFMqFZOdeG263S8v EegI222kjVxHJaMSSMRi3dTHZEDUuGg8c3ERP9AejrZfARyLT0 06aHLeqYBPAHCPNSYXt4nhB8ihU7fEzDV2souNIsI0l56G3td4 hcoIA6g9PIBmKlub3lcWfZ9slsKC8Hl1eWFh1OmJjjKsyO7fKJ SHm-bvZmRjaImOCJIaI7x1U9e6RITWFWtOqPIr6w4JQ9e7PG04A1ft xG6hkko6GsEi_Pt_f2zCZMs38UMuWfBkkK6iQliJ9SK5PeeBWu Z03tqm7HoeIHAM9UYHjuVuwuWd-gWdMQ3p5is7xaciiAODWWC15OyigrYG-nvxGXkxVIXuczBW9CUvEipQqeU1M2VdLsQJwRUde-f=w640
Click to enarge (https://lh3.googleusercontent.com/fL19JS3F0M01t7FPIfUrxCyUiDEiCqKV1nlDt6yBBVcG-w_q0sNPutLMYRdKOhCGx_uplpqXgp-2gBruNCtwQiR3pluApOkzhNNtKavtcedFpF9L_lXhnRjnixMIH P5iSfXgPz82iyCwdjjRhVMk8Kh2m3sw_HOLw9jlmt_bdLsUXA_ VTCE88zWCxYECzTbGjVXvd_MsfayTHHUrAyFMqFZOdeG263S8v EegI222kjVxHJaMSSMRi3dTHZEDUuGg8c3ERP9AejrZfARyLT0 06aHLeqYBPAHCPNSYXt4nhB8ihU7fEzDV2souNIsI0l56G3td4 hcoIA6g9PIBmKlub3lcWfZ9slsKC8Hl1eWFh1OmJjjKsyO7fKJ SHm-bvZmRjaImOCJIaI7x1U9e6RITWFWtOqPIr6w4JQ9e7PG04A1ft xG6hkko6GsEi_Pt_f2zCZMs38UMuWfBkkK6iQliJ9SK5PeeBWu Z03tqm7HoeIHAM9UYHjuVuwuWd-gWdMQ3p5is7xaciiAODWWC15OyigrYG-nvxGXkxVIXuczBW9CUvEipQqeU1M2VdLsQJwRUde-f=w1752-h985-no)

So I would recommend connect the 5151 to the 5150/5160 power supply to avoid phospor burns.

If i reboot the computer using RESET key, it produces the same vertical bright glow during reset period so i prefer ctrl+alt+del instead or try to push reset as short as possible.

retrogear
January 21st, 2016, 12:10 PM
I've always thought of RESET as hardware reset and c-a-d as software reset

SpidersWeb
January 21st, 2016, 12:24 PM
Maybe not. I have just acquired a 5151 (the one I had died) and it has a severe phosphor burn in the middle-bottom of the screen.


In that photo, all I can see is a pen mark?
Is that to cover the burn, or is the photo of something else?

retrogear
January 21st, 2016, 01:48 PM
Looks like a burn mark to me but with the CRT off, if you look with a strong magnifier close up off to the side of the mark, it's easy to tell if it's a mark on the glass or the phosphor.
I looked at my 5151 around the center with a magnifier and see no marks (yet)

PS - do in good room lighting, not with a lamp as direct light will cast a shadow of the mark onto the phosphor.

Larry G

nestor
January 21st, 2016, 01:53 PM
In that photo, all I can see is a pen mark?
Is that to cover the burn, or is the photo of something else?

It is not a pen mark, what you see is the burn. When this 5151 arrived I cleaned the screen in depth, at first I thought it was a mark in the glass but looking carefully... it's inside.

SquallStrife
January 21st, 2016, 02:11 PM
Maybe not. I have just acquired a 5151 (the one I had died) and it has a severe phosphor burn in the middle-bottom of the screen.


Such severe burn-in would take an extremely prolonged period of displaying that line, no question.

If that kind of burn-in occurred from a momentary flash, then the whole monitor would be damaged from text being displayed while the user reads it for a little while.

SpidersWeb
January 21st, 2016, 04:11 PM
It is not a pen mark, what you see is the burn. When this 5151 arrived I cleaned the screen in depth, at first I thought it was a mark in the glass but looking carefully... it's inside.

Interesting. I have a couple of screens with burn in, but I've never actually seen a black mark like that before.

Edit: although googling it shows lots of dark examples, I've just never come across it that bad before.

retrogear
January 21st, 2016, 06:40 PM
I'd seen several with phosphor burns in center of screen doing service on them for years. I remember a crt gun that was shorted and would intermittently snap. The center of the screen was peppered like a shotgun blast of buck shot.
In theory, I think it was pieces of oxide coming off the cathode being hurled at the screen.

Larry G

KC9UDX
January 21st, 2016, 06:45 PM
Such severe burn-in would take an extremely prolonged period of displaying that line, no question.

If that kind of burn-in occurred from a momentary flash, then the whole monitor would be damaged from text being displayed while the user reads it for a little while.

Yep, something's fishy.

But I have to disagree that the power-off beam-on phenomenon is always very quick. Maybe with solid-state monitors it is, I guess I never tried to find out. But on old black&white TVs, and some colour ones, the time of the beam-on state can be shown by bringing a magnet near the neck of the CRT, and moving it around. One set that I tried that on long ago had a dwell of two to three seconds (mind you the intensity diminished greatly). Still not enough to cause burn-in. But, the way I understand, all phosphor excitation causes some miniscule amount of burn, so the repeated spot over time (maybe too long to matter) will eventually burn in.

I have seen one black&white TV with an unfocused spot burnt in, but that may have been due to loss of deflection for some other reason. Oh, and that whole myth about colour monitors never burning in is just that. I've seen hundreds of colour CRTs with severe burn-in.

I'm not sure how to explain that line in this case. That doesn't make a whole lot of sense.

retrogear
January 21st, 2016, 07:09 PM
Are you talking about phosphor persistence? If you want to see that demonstrated, turn off a crt television while watching a show in a dark room and see how long you can see the last image on the screen.
As far as how a short vertical line could be burned in the lower half of the screen, I remember the really old b/w televisions when turned off the spot would actually travel down the screen before extinguishing.
I'm guessing that's due to gravity because the ions have mass. Maybe I read that in a book somewhere because I have no clue how I came up with that one ... :p

bobba84
January 21st, 2016, 07:38 PM
see how long you can see the last image on the screen.

At one stage, I had not turned on my 5151 for MONTHS (maybe even a year) and, while searching for something in the cupboard I had it stored in, I shone a torch at the screen. XTreeGold showed up legible enough to read the last few folders I had visited on it!

KC9UDX
January 21st, 2016, 08:18 PM
Are you talking about phosphor persistence?No, I'm talking about the total time that you see a "spot" when the power is turned off. Of course, when you turn the power off, three things turn off that affect this: the horizontal deflection, the vertical deflection, and the B++. Usually, the horizontal and vertical discharge pretty quickly, due no doubt to the low impedance of the deflection coils. But, the B++ takes a while to discharge. There are two timed events there: One is the time it takes for that to discharge, and then, when that is done, there's the time of persistence. The first can be observed by deflecting the beam, and the second can be observed only visually.


As far as how a short vertical line could be burned in the lower half of the screen, I remember the really old b/w televisions when turned off the spot would actually travel down the screen before extinguishing.
I'm guessing that's due to gravity because the ions have mass. Maybe I read that in a book somewhere because I have no clue how I came up with that one ... :p
Some of them did (do). Most that do that squiggle. I'm sure you know what I mean; the horizontal deflection is still barely running, and gets smaller exponentially, whilst the vertical falls. That in itself demonstrates the beam is still active, and that we're not just dealing with persistence.

On some sets, if you recall, the picture reduces to a spot, which stays in the centre, and then becomes severely unfocused before extinguishing.

As to why the beam falls in some, I have no explanation for that, you'd sure think it would migrate toward the centre. It can't be gravity, I don't think. Else the beam would fall any time you kill the vertical deflection. All those TVs with open vertical output transformers with that telltale horizontal line would have that horizontal line somewhere well below centre.

https://www.youtube.com/watch?v=39zeqy93cik
Also, turning a TV on its side would make it fall the other way!:)

In any case, if the beam is falling at power-off, I still wouldn't expect to see burn-in like that, due to the fact that the beam energy is greatly diminished by then. But who knows? I sure don't have a good explanation for why it's burnt like that. At least if it was a straight line, I'd say it's possible someone was monkeying round with it and killed the horizontal deflection and turned the vertical size down and off-centred it.

Hmm... I wonder if a momentarily greatly increased line voltage (line spike? lightning?) would cause the horizontal deflection to fail. That might explain it, rather remotely. But, if the horizontal oscillator stops, there shouldn't be any HV...

KC9UDX
January 21st, 2016, 08:26 PM
Heh, here's another common one: Vertical collapse and horizontal expansion. (faked of course)

https://www.youtube.com/watch?v=lB-bJWsIG_o

Now I'm going to have to make videos of all my TVs turning off.

SquallStrife
January 22nd, 2016, 02:01 AM
Yep, something's fishy.

My suspicion is that in a previous life, the monitor failed, and was left running in its failed state for some time before somebody noticed it, had it repaired, and the rest is history.

If there was some piece of text down at that position on the screen, and the horizontal coil became disconnected somehow (bad solder joint perhaps), then you'd get a super-intense vertical strip in one spot. It would only take a minute or two to wreck the phosphors in a scenario like that, I hazard.

retrogear
January 22nd, 2016, 03:01 AM
"Applying line frequency to vertical deflection"

Ah yes, the "hum" test. Dang, the memories that are coming back. When I was a young pup technician, I was taught while troubleshooting a vertical deflection problem,
a quick way to isolate whether the problem was in the vertical oscillator or output stages (I think it was all tubes in the circuit) was to actually hold a small value capacitor
(like maybe .01uf ?) in your fingers and touch the grid of the output tube. If the raster partially fills, the output stage was ok, go after the oscillator. Our small shop
couldn't afford the fancy test equipment in your video :p

PS - my morning caffeine is slowly awakening my memories. I think it was touch a .01 uf cap between the grid and a 60Hz AC source. I do remember just using my fingers if the
grid was a neutral voltage, though. Good thing my heart was young back then because I lived dangerously at my workbench.

PSS - it was to the filament AC voltage !! Ok I'll stop ...


Larry G

KC9UDX
January 22nd, 2016, 04:07 AM
My suspicion is that in a previous life, the monitor failed, and was left running in its failed state for some time before somebody noticed it, had it repaired, and the rest is history.

If there was some piece of text down at that position on the screen, and the horizontal coil became disconnected somehow (bad solder joint perhaps), then you'd get a super-intense vertical strip in one spot. It would only take a minute or two to wreck the phosphors in a scenario like that, I hazard.

I keep thinking like a TV, and in that case, it couldn't be that simple. But you're right, in the case of a monitor, with never moving text in that part of the screen, it does make sense.

I'd still expect to see a very straight vertical line, which that one doesn't look like to me. But, it must be, and just doesn't look like it from here. Because what you're describing is the only thing that makes sense.

KC9UDX
January 22nd, 2016, 04:52 AM
I just explained that video and all my follies with the hum test and my post vaporised. Well I'm not typing all that again. :mad:

But I'll post the sequel video because it's fitting .

https://m.youtube.com/watch?v=pNfNX2d8NVk



What did I do to anger the forum software???

retrogear
January 22nd, 2016, 06:03 AM
I went thru a period of time losing posts but then suddenly had no problems. To play it safe, I do the cut and paste to notepad if the post is long enough. I'm thinking it was a funky drop
of internet connection maybe even at my end. Sucks, though ... Would like to have read your post. I know we are comrade TV repairmen. Maybe it's the vodka :p

Larry G

Stone
January 22nd, 2016, 07:09 AM
This forum automatically saves unfinished/mid-stream posts and will restore them upon user request. As I am typing this the yellow 'Auto-Saved' indicator is intermittently flashing in the lower righthand corner of the text box. I know it works as I've used the restore feature many times. :-)

KC9UDX
January 22nd, 2016, 07:37 AM
I must have a different text box.

Actually, probably so. I think I changed editors to be able to use IBrowse.

Stone
January 22nd, 2016, 07:56 AM
Everything comes at a cost! :-)

PhilipA
January 25th, 2016, 03:17 PM
My 5151 could be persuaded to not produce a bright-bright line then dot by turning the brightness dial to max before switching the computer (which was providing the switched supply for the screen) off.

I had a Sony TV set that would do that also, a little monochrome portable- if the brightness dial was dialed to the dimmest and the set switched off you'd see the raster collapse in a big upside-down pine-tree shaped wiggle and settle to a dot in the middle of the screen.

I had discussed this with someone and apparently there's supposed to be a capacitor that holds enough charge on power-down to hold the blanking circuit active until the HT is bled off.. I'm not sure how well that works in practise (or even theory) though.

--Phil

retrogear
January 25th, 2016, 03:57 PM
There's patents here: http://www.google.com/patents/US5920339
Essentially a capacitor is kept charged during operation and when power is turned off, the charge held on the capacitor floats the control grid G1 extremely negative to cut off the CRT beam current.
I think I see the problem with the 5151. Looking at the control grid schematic, the -167 G1 bias voltage feeding the brightness control has no capacitor to sustain the negative bias after the flyback shuts down, but C514 maintains a 50V positive
charge on the other end of the brightness control after power off, so the G1 will actually swing positive to turn on the CRT hard, strange ...

Larry G