Author Topic: Faulty Monitors  (Read 309 times)

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Offline geebus

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Faulty Monitors
« on: 17:59, 30 November 18 »

Anyone got any advice for working on the monitors? I believe them to be the CTM644. I know there are precautions I need to take when opening it, I'm sure i'll find out those on here somewhere after a bit of searching.


More looking for advice on where to start with fixing the 12v output and the h or v-sync if anyone has any experience with those.


I'm totally new to this, hell I don't even have the screens at home yet. Just excited to have them in my ownership even if they are a couple of hundred miles away just now.
Getting prepared!

Offline Bryce

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Re: Faulty Monitors
« Reply #1 on: 13:39, 02 December 18 »
These monitors have a 20kVDC charge on the tube and a 400VDC charge in one of the capacitors on the mainboard, even when it has been unplugging for days. So if you don't know exactly what you are doing, I would suggest no touching them! It may end up being your last repair.


Bryce. 

Offline geebus

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Re: Faulty Monitors
« Reply #2 on: 12:01, 03 December 18 »
Hi Bryce,
Thanks for the comment. I'm aware that there are high voltages stored within the monitors. I was hoping for some advice on checking there was no charge in them. Or how to discharge them.
Everyone starts somewhere, and i'm aware of the danger involved with opening up CRT devices.
I'm not going to do anything with them unless i know EXACTLY what i'm doing. Because I don't fancy having 20kV through me..
Thats an insane amount of voltage!


I'm assuming there is some way of earthing and discharging all the voltages that are held within the screens?


If no one is willing to advise on how to do it (for fear I might fry myself trying), Can anyone advise on someone who is able to do the repairs for me?


I would rather Learn how to do these repairs myself. I'm apprehensive about it, but want to learn.

Offline Bryce

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Re: Faulty Monitors
« Reply #3 on: 13:16, 03 December 18 »
The 20kV is in the big red cable going to the suction cup on the back of the tube. Before you do anything, check (without touching) that there are no cracks in the insulation. If the cable looks healthy and you aren't swapping the tube or the LOPT, then just leave this alone. It doesn't need to be discharged unless you need to remove the suction cup connection.The 400VDC is in a big black capacitor (see picture below). It has two pins on the under side of the PCB. This definitely needs to be discharged. You can do this by either measuring the charge with a LoZ meter if you happen to own one, or if not, make yourself a discharge bulb: Standard 240V Bulb with two insulated wires attached. Touch the ends of the wires across the two capacitor terminals and the bulb will make a very short, extremely bright flash. Give it a second go to ensure it really fully discharged.

However, quick warning: Capacitors tend to self-charge if left open (which this one is), so you might get a small tingle if you touch it a few minutes later, but this isn't dangerous, just annoying.


And a last piece of advice: Never work on things like this if you are home alone. Make sure someone is there to call the ambulance if something goes wrong, because you won't be doing it.


Bryce.




Offline geebus

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Re: Faulty Monitors
« Reply #4 on: 13:34, 03 December 18 »
Thanks Bryce!
I'll have the gopro running so that people can watch what I done wrong at my autopsy...


On a serious note. Thanks. Make it look much less scary than i had in my head.

Offline remax

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Re: Faulty Monitors
« Reply #5 on: 15:24, 09 December 18 »
I know nothing about all that but it seems there is an important advice about having a hand in the back while working on things like that.






I heard another advice about doing all the work with barenaked foot drowning in water, but i'm not sure of that one  ;D

Offline geebus

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Re: Faulty Monitors
« Reply #6 on: Yesterday at 17:49 »
Just thought I'd update this a little.


One of my brothers is just back from working away and he deals with high voltage equipment on oil rigs.
So I asked him about working on the CRT monitors and he stated that I needn't be worried about the 20kV line trying to kill me as it just wont (unless i leave it plugged in). As he said "I've been electrocuted countless times with 18kV" and "it'll only tickle, Not much current in the high voltage stuff".


I also done a bit more reading on the subject and came across this post.
https://lowendmac.com/2007/the-truth-about-crts-and-shock-danger/


I'll still be cautious about it and do it properly, thats for sure!
But not as worried that I'm going to leave my wife a widow and my daughter fatherless just because I wanted to relive some of my childhood gaming experiences.

Offline Bryce

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Re: Faulty Monitors
« Reply #7 on: Today at 09:46 »
The article is interesting and mostly correct (slightly inaccurate for Europe as he based his calculations on an american monitor). And he is correct in saying that it probably won't (but could) kill you. His comparison of joules of energy in a calorie is just stupid though. They are in completely different forms, so it's like saying: My kid won't drown in the paddle pool, because a fridge freezer holds the same amount of water and he doesn't drown when he opens the freezer door!


However, speaking from experience, it is one of the most painful and scary experiences you will ever have the displeasure of going through. It will leave a huge burn along the skin which takes months to heal and leaves a scar, it will lame you for minutes and it will definitely mean a night in hospital. And that's only if you are in a fit enough condition to survive it.

Unfortunately I no longer own the correct equipment to measure the charge on a CRT, but my guess is that it's above 1 joule too.


That's why I tend to warn people away from this area.

Bryce.

Offline geebus

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Re: Faulty Monitors
« Reply #8 on: Today at 12:12 »
Ouch, sounds like you had a fun time!
How did you manage that!?


I was going to inquire about the power that was held within that 20kv. I might need to delve deeper into it. With reading I mean.. I'm not going to stick my fingers in there, one from each hand JUST to make sure.

Offline Bryce

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Re: Faulty Monitors
« Reply #9 on: Today at 13:53 »
Well you'll often hear the incorrect "It's the volts (or amps) that kill you" statments. The total energy available (Joules) and the rate at which they can be discharged is what makes the difference. This is why the "Joules in a Calorie" comparison is laughable. There are around 13,000 joules in an AA battery, but it's not going to kill you (unless you eat it or it gets shot at you), because it has an ESR (Equivalent Series Resistance) that slows the rate of discharge. A gram of TNT on the other hand is equivalent to about 14 AA batteries as far as total energy capacity is concerned, but the TNT can release it's entire energy in nano-seconds and do quite a bit of damage, 14 AA batteries aren't going to hurt you even if you connect them all together.


A capacitor (a CRT is effectively a very high voltage capacitor) can discharge its entire capacity almost instantly, which is what makes capacitors more dangerous than other components. So the question is, how many joules can the CRT hold and how fast can they get out? The physical size of the CRT defines its capacity. The higher voltage indirectly determines how fast the energy can get out. And when they get out they hurt.

Bryce.