exxos's Atari, Amiga & retro forum

mgi wrote: 09 Jan 2022 09:37 After Xmas I had a chance to look into my broken sc1435. Since I could not find anyone who is willing to work on old CRT I did some digging and the most likely culprit for no picture and whining noise was flyback transformer. I replaced it yesterday and the noise is gone, screen is coming up but after few seconds it starts blinking and making unhappy noises: https://youtu.be/tc2Y4TXTZyY

Have you got any signal going into the monitor in that video? Do you have the contrast knob set around midpoint or lower? If the answers are no and yes, then it looks like you've got the voltage set way too high on the flyback. The screen should not be coming up that bright. The flyback has two knobs on it. One of them is focus and the other is voltage (usually labelled "screen"). Turn the screen knob fully anticlockwise (preferably with the monitor off and discharged for safety) and then power it back up again and see if your problem is gone.

If that resolves the problem, bring the voltage back up very carefully (use a plastic screwdriver) until you get a good picture.

Good advice @derkom . I forgot about the flyback adjustments.

OK, I turned it off to the minimum and the effect stopped but the screen is dark. So what're next steps?
Slowly turning to the right and when should I stop?

mgi wrote: 09 Jan 2022 14:17 OK, I turned it off to the minimum and the effect stopped but the screen is dark. So what're next steps?
Slowly turning to the right and when should I stop?

Set the contrast knob (not the screen knob on the flyback!) at the centre, give the monitor a signal so you've got something to look at--the desktop on your ST is fine--and then turn the screen knob clockwise until you've got a satisfyingly bright picture with no blooming. There are proper test patterns for adjusting these things, but honestly you can just eyeball it. Unfortunately this adjustment must be done with the monitor powered up (unless you want to do it in lots of small steps), so it is recommended to use a plastic screwdriver or a HV-safe screwdriver, and of course still be careful. It's not hard to do, but certainly a little bit nerve wracking!

IT IS WORKING!!!!

BIG THANKS!

:girldance: :2k2: :girldance:

Well done!

Great job that you fixed it yourself. :D

Very happy indeed!
I guess you could tinker with those adjusters but I am happy and don't want to mess too much :)

mgi wrote: 09 Jan 2022 14:55 Very happy indeed!
I guess you could tinker with those adjusters but I am happy and don't want to mess too much :)

Sure, if you see later that the image is blooming a little, or that you're having to pull the contrast too high to get the intensity you like, you might tweak the screen knob a bit. But generally speaking you can eyeball it fairly well.

Also you can adjust the focus knob and see the effect you get there. Sometimes an image that you think is in focus is actually out a little. Focus is very easy to eyeball.

Thanks a lot! It is working now, looking good and I am very pleased!
This forum is so helpful!