VOGONS


First post, by red_avatar

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Yesterday I went to pick up a "perfectly working" ViewSonic E771 CRT. ViewSonic made really good CRTs so I was willing to drive two hours to get it for cheap.

However, when I plugged it in, it was obvious something was really wrong: the image was set to minimum horizontal wideness and still didn't fit the screen. The sides were also distorted and the center was too wide than it should be.

I opened it up, cleaned it up, tugged on all wires a little to make sure nothing was lose, plugged it in, set all values to "normal" and ... it worked fine ... for 15 minutes. When I ran off and came back, it was way too wide again.

The rest of the screen is in excellent condition - the inside was remarkably clean, the image was perfectly sharp and vibrant - basically NOTHING was wrong with it.

I suspect maybe one or more caps went bad but I can't see any bulging. Does anyone have any idea if this is worth fixing?

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Reply 1 of 20, by Tiido

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That seems like some capacitor in the deflection circuitry is causing it, possibly a cold solder joint since you managed to get good image.

If you are willing, run the thing open, and use some non conductive thing (plastic rod equivalent) and tap various bits and see if you can find the culprit.

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Reply 2 of 20, by red_avatar

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Tiido wrote on 2021-09-11, 11:37:

That seems like some capacitor in the deflection circuitry is causing it, possibly a cold solder joint since you managed to get good image.

If you are willing, run the thing open, and use some non conductive thing (plastic rod equivalent) and tap various bits and see if you can find the culprit.

Well I gave this a go but there's only one huge board below and the board at the back of the yoke and that one is in a shield that is heavily soldered on. I prodded the components which I reached with zero result. I took a flashlight to solder joints and they all look healthy though ...

Hmm it would be a darn shame to throw this one out. I wish there were still local TV repair people.

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Reply 3 of 20, by Anonymous Coward

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Viewsonic monitors were very nice when new, but at least the ones from the late 90s didn't seem to last very long. I knew a whole bunch of people that had them, including myself and they usually only lasted about 3 years with casual use. Maybe they had a bunch of those leaky capacitors in them.

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Reply 4 of 20, by Tiido

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The fault is likely to be in the zoo near the flyback transformer, probably the larger components. The closed up box attached to the neck is only video amps etc., there won't be anything that affects geometry there.

Can you take a photo of the image and perhaps some of the main board itself ?

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Reply 5 of 20, by red_avatar

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Anonymous Coward wrote on 2021-09-11, 12:44:

Viewsonic monitors were very nice when new, but at least the ones from the late 90s didn't seem to last very long. I knew a whole bunch of people that had them, including myself and they usually only lasted about 3 years with casual use. Maybe they had a bunch of those leaky capacitors in them.

I hope not - it's a shame that quality hardware dies because of short term greed.

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Reply 6 of 20, by red_avatar

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Tiido wrote on 2021-09-11, 12:47:

The fault is likely to be in the zoo near the flyback transformer, probably the larger components. The closed up box attached to the neck is only video amps etc., there won't be anything that affects geometry there.

Can you take a photo of the image and perhaps some of the main board itself ?

Thanks for helping me out. Here are a few images - lemme know if you need more. I also found the schematics online of all electronics but that's not something I can read ...

IWZkpec.jpg
dmyJJbV.jpg
61HbiVW.jpg
72lMAl3.jpg
sm9aEu6.jpg

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Reply 7 of 20, by Tiido

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That looks like a problem around what is called S correction. One of the fat capacitors seen on the last insides photo is responsible for correcting for it though the way things work is that if there's a problem the sides should be expanded rather than compressed...

It is worth trying to exercise all the connectors if you haven't already.

Can you attach the schematics to the post ? I would like to take some looks at it.

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Reply 8 of 20, by rmay635703

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What resolution/refresh rate are you using?
I’ve had screens that work fine at 60hz vga 640x480 but flake out at 800x600x72

If you can’t fix it or don’t care to
internally there should be pots for various geometry settings along with the cathode voltage.

You can manually shrink the screen size internally

You can also play with the cathode voltage
One “jumpy” screen I had would stabilize with the voltage turned down a bit (dimmer image)
After adjusting the geometry internally I lived with it as is many years.

Some Failing CRTs can operate in failure many years (depending on the failure)

It looks to me like the distorted area is small enough you could live with it if you can’t find the fault

YMMV, I never would throw out a worn screen, would just get it usable enough and live with it. Had good luck with durability after adjustment, only had a couple that literally could only be tossed, but I was known to solder jump wires over bad traces and failed switches

Good Luck

Reply 9 of 20, by red_avatar

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Tiido wrote on 2021-09-11, 18:29:

That looks like a problem around what is called S correction. One of the fat capacitors seen on the last insides photo is responsible for correcting for it though the way things work is that if there's a problem the sides should be expanded rather than compressed...

It is worth trying to exercise all the connectors if you haven't already.

Can you attach the schematics to the post ? I would like to take some looks at it.

From what I read, you're on the right path with S correction since this sounds quite right - it's typical for later-end CRTs that were shorter than usual from what I read.

Tomorrow I'll unplug and replug all connectors and see if I notice anything else in that area. The diagram I have is ridiculously complicated but perhaps it will still be of some use if all my replugging does nothing.

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Reply 10 of 20, by red_avatar

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rmay635703 wrote on 2021-09-11, 18:54:
What resolution/refresh rate are you using? I’ve had screens that work fine at 60hz vga 640x480 but flake out at 800x600x72 […]
Show full quote

What resolution/refresh rate are you using?
I’ve had screens that work fine at 60hz vga 640x480 but flake out at 800x600x72

If you can’t fix it or don’t care to
internally there should be pots for various geometry settings along with the cathode voltage.

You can manually shrink the screen size internally

You can also play with the cathode voltage
One “jumpy” screen I had would stabilize with the voltage turned down a bit (dimmer image)
After adjusting the geometry internally I lived with it as is many years.

Some Failing CRTs can operate in failure many years (depending on the failure)

It looks to me like the distorted area is small enough you could live with it if you can’t find the fault

YMMV, I never would throw out a worn screen, would just get it usable enough and live with it. Had good luck with durability after adjustment, only had a couple that literally could only be tossed, but I was known to solder jump wires over bad traces and failed switches

Good Luck

Trust me, it's impossible to use like that - and there's no pots to adjust to compensate. I found the typical adjustment pots for the three colours as well as their alignment + two for focus (horizontal and vertical) and one for brightness. That's it.

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Reply 11 of 20, by rmay635703

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red_avatar wrote on 2021-09-11, 20:40:
rmay635703 wrote on 2021-09-11, 18:54:
What resolution/refresh rate are you using? I’ve had screens that work fine at 60hz vga 640x480 but flake out at 800x600x72 […]
Show full quote

What resolution/refresh rate are you using?
I’ve had screens that work fine at 60hz vga 640x480 but flake out at 800x600x72

If you can’t fix it or don’t care to
internally there should be pots for various geometry settings along with the cathode voltage.

You can manually shrink the screen size internally

You can also play with the cathode voltage
One “jumpy” screen I had would stabilize with the voltage turned down a bit (dimmer image)
After adjusting the geometry internally I lived with it as is many years.

Some Failing CRTs can operate in failure many years (depending on the failure)

It looks to me like the distorted area is small enough you could live with it if you can’t find the fault

YMMV, I never would throw out a worn screen, would just get it usable enough and live with it. Had good luck with durability after adjustment, only had a couple that literally could only be tossed, but I was known to solder jump wires over bad traces and failed switches

Good Luck

Trust me, it's impossible to use like that - and there's no pots to adjust to compensate. I found the typical adjustment pots for the three colours as well as their alignment + two for focus (horizontal and vertical) and one for brightness. That's it.

If there aren’t adjustment pots it would be an electronic service menu setup, that said you can cut traces and make your own adjustment pots but by that point you may as well find the actual fault.

For my humor with a plastic screwdriver try turning the “as you call it” brightness adjustment far up and down while the fault is occurring

You might get a pop and a jump in the image.

Reply 12 of 20, by red_avatar

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rmay635703 wrote on 2021-09-11, 21:14:
If there aren’t adjustment pots it would be an electronic service menu setup, that said you can cut traces and make your own adj […]
Show full quote
red_avatar wrote on 2021-09-11, 20:40:
rmay635703 wrote on 2021-09-11, 18:54:
What resolution/refresh rate are you using? I’ve had screens that work fine at 60hz vga 640x480 but flake out at 800x600x72 […]
Show full quote

What resolution/refresh rate are you using?
I’ve had screens that work fine at 60hz vga 640x480 but flake out at 800x600x72

If you can’t fix it or don’t care to
internally there should be pots for various geometry settings along with the cathode voltage.

You can manually shrink the screen size internally

You can also play with the cathode voltage
One “jumpy” screen I had would stabilize with the voltage turned down a bit (dimmer image)
After adjusting the geometry internally I lived with it as is many years.

Some Failing CRTs can operate in failure many years (depending on the failure)

It looks to me like the distorted area is small enough you could live with it if you can’t find the fault

YMMV, I never would throw out a worn screen, would just get it usable enough and live with it. Had good luck with durability after adjustment, only had a couple that literally could only be tossed, but I was known to solder jump wires over bad traces and failed switches

Good Luck

Trust me, it's impossible to use like that - and there's no pots to adjust to compensate. I found the typical adjustment pots for the three colours as well as their alignment + two for focus (horizontal and vertical) and one for brightness. That's it.

If there aren’t adjustment pots it would be an electronic service menu setup, that said you can cut traces and make your own adjustment pots but by that point you may as well find the actual fault.

For my humor with a plastic screwdriver try turning the “as you call it” brightness adjustment far up and down while the fault is occurring

You might get a pop and a jump in the image.

I found two more pots hidden away underneath the tube. One seems to affect the wavelength (or whatever you call it - it stars rolling left or right if I turn it) and the other moves the image left or right. When I touched the second one, suddenly the monitor popped back to "normal". I thought "hey maybe it's just a dirty pot!" but nope, after 10 minutes it jumped back.

I did like you said and turned all pots to the extremes but no result. I still need to unplug all the connectors though - I 'll try that tomorrow morning.

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Reply 13 of 20, by retardware

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Tiido wrote on 2021-09-11, 18:29:

Can you attach the schematics to the post ? I would like to take some looks at it.

Schematics would help saving time when resoldering the soldering joints, because you then can limit the work to the areas actually being in question.
Keep in mind that the heavy stuffs's soldering tends to more cold soldering problems than the small ones because it does not heat up as well as the small stuff when taking the short journey through the solder bath.
Resoldering the stuff in the flyback area should take only a few minutes.

Btw, prodding/knocking is not a reliable method, as the result is quite random.

Possible, but unlikely is a partial short in the flyback transformer or deflection coils that opens when the stuff expands when warming up.
Faulty connectors or potentiometers are not very probable, either, imho.

Reply 14 of 20, by red_avatar

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retardware wrote on 2021-09-11, 22:57:
Schematics would help saving time when resoldering the soldering joints, because you then can limit the work to the areas actual […]
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Tiido wrote on 2021-09-11, 18:29:

Can you attach the schematics to the post ? I would like to take some looks at it.

Schematics would help saving time when resoldering the soldering joints, because you then can limit the work to the areas actually being in question.
Keep in mind that the heavy stuffs's soldering tends to more cold soldering problems than the small ones because it does not heat up as well as the small stuff when taking the short journey through the solder bath.
Resoldering the stuff in the flyback area should take only a few minutes.

Btw, prodding/knocking is not a reliable method, as the result is quite random.

Possible, but unlikely is a partial short in the flyback transformer or deflection coils that opens when the stuff expands when warming up.
Faulty connectors or potentiometers are not very probable, either, imho.

Here's the schematics I found:

https://i.imgur.com/Hwovkjo.png
https://i.imgur.com/70ubKc0.png

I hope that helps.

So you're saying I should try reflowing the components involved?

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Reply 15 of 20, by retardware

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red_avatar wrote on 2021-09-11, 23:23:

https://i.imgur.com/70ubKc0.png

So you're saying I should try reflowing the components involved?

The flyback stuff is in the second schematics in the right part.

There are some large stuff (caps, coils, resistors, big transistors etc with thick wires) that don't get heated well in the normal flowing bath.
These tend to get loose with time. Vibration and oxidation does its work also.
Back in the CRT TV ages it was usually sufficient to reflow these using a hot soldering iron (50-80W) and adding a bit solder wire with flux core.
The heavy 1960s and 1970s TVs were a PITA because the convergence units were large and got very hot, making reflowing a lot of work. This is luckily not the case with your monitor...

Edit: Make sure not to solder too quickly, as you want to make sure that the thick wires get hot. So also take care that the iron tip touches the wire itself, not only the pad.

Reply 16 of 20, by Tiido

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Poking around was worth a shot, especially since previous look inside did restore operation briefly. It certainly seems like a mechanical problem and resoldering various bits in the line and HV stage would probably make a positive difference.

The area of interest is mostly confined into the area seen here :

AreaOfInterest.png
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Reply 17 of 20, by rmay635703

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retardware wrote on 2021-09-11, 22:57:

Faulty connectors or potentiometers are not very probable, either, imho.

Faulty no but they can be used to find the components causing the fault,

On some “bad” screens turning the drive voltage up can make cool pyrotechnics and drive the fault making it a visual indicator

Reply 18 of 20, by red_avatar

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I believe I found the cause of the malfunction: while reflowing the components, I noticed one component had no solder around its leg and a clear gap could be seen between the leg and the circuit. If this was indeed the cause, it explains why the problem was intermittent. I still reflowed some 80 components since I was doing it anyway, turned it back on and voila, immediately perfect image!

I'll leave the monitor running for a good hour - if it doesn't "jump" back I'll consider it fixed.

Thank you for all the help! I really appreciate it, especially for something for which so little information is to be found online. It's as if CRT repair is a close guarded secret considering how few tutorials there are.

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Reply 19 of 20, by Tiido

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Congratulations ~

The biggest resource online I know of is this : https://www.repairfaq.org/sam/tvfaq.htm
A lot of good info is condensed on these pages.

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