VOGONS


First post, by DaveJustDave

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Recently picked one up. The display takes a while to "warm up" (much more so than the Princeton EGA monitor I have) and it's pretty dim and fuzzy.

Does anyone know if there's anything I can adjust inside the chassis ? I was planning on going in there anyways and seeing if any capacitors need to be replaced.

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Reply 1 of 11, by keropi

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Capacitors are a good start , then the LOPT "SCREEN" pot is another and/or the RGB pots on the nechboard. Tubes and guns tend to degrade over time so re-adjustment might be the answer.

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Reply 2 of 11, by DaveJustDave

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keropi wrote:

Capacitors are a good start , then the LOPT "SCREEN" pot is another and/or the RGB pots on the nechboard. Tubes and guns tend to degrade over time so re-adjustment might be the answer.

thanks for the information! whats the best way to discharge the capacitors so I don't turn myself into a vegetable?

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Reply 3 of 11, by keropi

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I have worked with several monitors in the last year - from 1084s to VGA and even 28" arcade ones, I never had to worry about capacitors. Just pay attention to the input one (or two) it is the largest one near the power cord connection and depending your region they are rated for 200~400V. Just don't touch both ends at the same time 🤣
Maybe allow 24hrs for them to drain and work without fear on the chassis.
BUT
you will need to discharge the tube, that's where the real danger is. Maybe there is a bleed capacitor to do that automatically but don't risk it and remove that suction cap without discharging it manually first , here is what you need to do: https://www.youtube.com/watch?v=-jbnFuVWTdk
Personally I am using the building's GROUND in the power sockets to discharge the tube - it just makes me feel better to do so rather than using the monitor itself.

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Reply 4 of 11, by Anonymous Coward

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Did you see my post about the brightness/contrast knobs? I think in order to adjust brightness you have to pull out the knob before turning it, otherwise it has no effect.

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Reply 5 of 11, by dkarguth

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keropi wrote:

Personally I am using the building's GROUND in the power sockets to discharge the tube - it just makes me feel better to do so rather than using the monitor itself.

I know this is a very old thread, but I can't let this bit of misinformation remain in good conscience. 'Discharging' the tube through earth ground does not discharge the tube at all! The only way to properly discharge the tube is to bleed off the charge to the ground strap on the tube. The tube is basically a huge capacitor. It would be like connecting the positive lead of your car battery to earth ground; you aren't discharging the battery at all.
Discharge your tube to monitor ground, not earth ground. Failing to do so can be the last mistake you ever make.

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Reply 7 of 11, by keropi

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yes chassis instead of ground is better because you get to equalize the tube that acts as a capacitor
I did many repairs with ground , they all popped and no issues afterwards but this doesn't mean it's correct so better be safe

retardware wrote:

And what I do not understand, too, for what reason is it necessary to discharge the tube, unless it is going to be replaced?

if you want to work on the chassis you'll most likely remove the anode cap so discharging the tube is a good idea

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Reply 8 of 11, by retardware

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keropi wrote:
retardware wrote:

And what I do not understand, too, for what reason is it necessary to discharge the tube, unless it is going to be replaced?

if you want to work on the chassis you'll most likely remove the anode cap so discharging the tube is a good idea

But for what reasons except for CRT or horizontal output transformer replacement does one need to detach the anode cap???

Reply 9 of 11, by keropi

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to take out the chassis pcb from the monitor assembly for inspection and repairs - way easier to work with it removed than on the whole assembly

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Reply 10 of 11, by dkarguth

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retardware wrote:
keropi wrote:
retardware wrote:

And what I do not understand, too, for what reason is it necessary to discharge the tube, unless it is going to be replaced?

if you want to work on the chassis you'll most likely remove the anode cap so discharging the tube is a good idea

But for what reasons except for CRT or horizontal output transformer replacement does one need to detach the anode cap???

Ever tried to work on an old IBM monitor with the electronic subassembly still in the chassis? I assume not, as you literally can't do anything with the huge tube in the way. Also, it is just good practice to discharge the tube. It completely eliminates the chance that you get shocked if a screwdriver slides underneath the cap, or the insulation on the anode wire was pinched, or any other number of things. Why take the chance? It takes literally 10 seconds to discharge the tube, so might as well do it.

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Reply 11 of 11, by retardware

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dkarguth wrote:

... or the insulation on the anode wire was pinched, or any other number of things. Why take the chance? It takes literally 10 seconds to discharge the tube, so might as well do it.

You are completely right... seeing pinched HV cables is nightmarish.
And not seeing a pinch before handling the cables can result in a nice zapping... had that once.

But doing the discharge correctly and safely is difficult...
I don't consider it a safe practice to use a screwdriver that is certified to 5kV or typically much less.
If the wire has bad contact to the screwdriver or the ground clamp pops off, this can get DANGEROUS.

For this reason it was common in the TV industry not to discharge unless working at the HV components, as the discharge process requires a HV probe with at least 30kV insulation (see the image in this page), which will discharge the tube safely via the measuring divider (the tubes' capacity is "only" about one microfarad, and shorting caps is generally bad).

And often not mentioned in the "CRT discharge guides" also is the phenomenon of charge re-buildup, which is why you have to discharge several times over at least 1h, better more.

So it is often less risk and time consumption if you only discharge the CRT if really needed.
At least this was the perception with the 1960s and 1970s repair TV literature with which I learned to fix TVs.