General Discussion on Misbehaving CRTs

[rjd324]

Firstly, I do not know much about CRTs than terms that I have picked up over the recent months. I have only opened them up, dusted them off, replaced a switch.


I have also has correspondence with a member or two on here who know their stuff, but a general thread and more information from more people is always good.


I pulled my old DAEWOO monitor out and I also have a DELL d1028lr. Both of them, after being on for a while, suffer from the same artifact. After a while of use I hear a "POP" and the screen expands and then shrinks back to normal. I have heard that it could be a cracked flyback.



- Is a cracked flyback also the opinion of other people?
- Why have I never seen this happen on any of my commodore monitors (1083s and M1438s)
- If it is the flyback, is it not a coincidence that it has happened on both these monitors? If not, it must be a common issue that cracks occur after 20+ years...
- Is an epoxy method worth it over sourcing a "new" flyback?

[Bruce Abbott]

Originally Posted by rjd324

I pulled my old DAEWOO monitor out and I also have a DELL d1028lr. Both of them, after being on for a while, suffer from the same artifact. After a while of use I hear a "POP" and the screen expands and then shrinks back to normal. I have heard that it could be a cracked flyback.

The 'pop' is probably an arc-over in the EHT circuit, perhaps inside the transformer but it could be somewhere else. The screen expands because when the EHT voltage drops the electron beam is accelerated less so the deflection coils have a greater effect.

If you are lucky it might just be dust, grime, or moisture around the Anode connection on the tube (under a large synthetic rubber 'boot' which is supposed to keep the area clean). Other parts near the EHT transformer also have high voltage across them and so attract dust which could cause arc-overs.

If the monitor detects (what it thinks is) too much EHT voltage then it will shut down to avoid generating X-rays. So it could be that the EHT voltage regulation or detection circuit is failing, perhaps due to a a 'dry' (cracked) solder joint in the area. Some Monitor models are prone to getting dry joints on the EHT transformer pins because it is a large heavy item which puts stress on the PCB.

- Why have I never seen this happen on any of my commodore monitors (1083s and M1438s)

You have been lucky.

- If it is the flyback, is it not a coincidence that it has happened on both these monitors?

Perhaps they have been stored in a damp environment, or perhaps it's just coincidence that both are starting to fail with age.

If not, it must be a common issue that cracks occur after 20+ years...
- Is an epoxy method worth it over sourcing a "new" flyback?

In my experience most EHT transformer failures are permanent, and they cannot be repaired. Filling cracks with epoxy might work, but if you want to ensure that your monitor can always be repaired then keeping a spare EHT transformer for it is not a bad idea.

[rjd324]

Thanks for the info. Can you use any replacement flyback so long as it fits?

I started another thread that I think would be useful for people if we could start a mapping of monitor versions to replacement flyback versions.

[Jope]

Just fitting probably is not enough, you need to buy an equivalent flyback that is correct for your chassis.

[Bruce Abbott]

It has to be exactly the right one - so if you find one grab it! Hard to believe that the correct spares would still be available after all these years.

[Jope]

Guys like Donberg actually have new ones made as stock runs out.

[rjd324]

Does anyone know anyone that still repairs CRTs? In the North of UK would be ideal.

I have;

- dell 1028lr that works great then starts to arc every so often but still works, but for the occasional time when I turn it on and the picture starts off as a small dot in the centre of the screen and then the picture expands, expands and then all I see is black. But kind of working when that doesn't happen.

- Daewoo 518x that when I turn on just makes these sort of crackling noises and there is no picture. Was working before with arcing after been on for a while. Eventually one night it decided to turn on and off repeatedly and a resistor started smoking right near the fbt. I have replaced the fbt and the reaisitor on the hope of repair but I am seriously np expert!

- some siemens that also kind of works until after a while it just turns off and then comes back to life.

- an amiga monitor: m1438s which works... Except.... Sometimes when I turn it on I only get a black screen. If I turn it off then turn it on then it works. This appears to be random. And this happens from cold or hot. Occasionally a horizontal line flickers on the screen.

The only solid monitor I have is my 1083s, and I might as well get that serviced too.

I can do general soldering and repairs but when it comes to CRTs... I'll leave that to the guys that actually know their stuff.

So I am wondering if someone in the North UK exists.

Regards. (there may be mobile phone typos)

[rjd324]

https://streamable.com/rauqr9

Here is a video of what the Dell does after I may have turned the monitor off for 20 minutes to do something.

[dreadnought]

Your best bet is probably posting a classified ad. There might be some retired CRT technicians or hobbyists who have experience fixing them in your area.

But tbh I wouldn't bother trying to fix common PC VGA monitors - these can still be found quite cheap or free. Again, classifieds. On ebay everyone wants to make bank on even the most mundane items.