CRT colour monitor Screen intermittant jumping

[roadrash]

I have a very old Viglen CRT monitor that looks like its about to fail at any moment.
While I was using it to display MSOS text the display started jumping and text shrinking and then expanding in size again. Its looks like the display is about to collapse and disappear at any moment. Is this a Cap or dry joint problem and can anyone point me as to whats likely failing and where to look for it before it completely fails.

[stj]

Re: CRT colour monitor Screen intermittant jumping

vertical lock failure - it's going to be a small electrolytic or bad soldering on the vertical chip.

[roadrash]

Re: CRT colour monitor Screen intermittant jumping

Thanks for that info. I used it this morning for a few hours and it behaved for ages then started playing up again. Anyway I've took some pictures of it so hopefully you can point me to where I should be looking for the vertical lock fault or what ever it is.

[stj]

Re: CRT colour monitor Screen intermittant jumping

first thing you need to do is pull the chassis out and chack the soldering on anything large or fixed to a bracket/heatsink or anything that could lever or flex it.
bad soldering is the no.1 problem on old tvs & monitors.

[roadrash]

Re: CRT colour monitor Screen intermittant jumping

Just took some more pictures I can look through on the PC and zoom in on. Then when I see something suspicious I can investigate. I havent seen anything obvious, no domed or leaking caps but there are some discoloured areas and one that looks like it could be burnt near a 100ohm resistor (R628 picture 1.jpg above EHT transformer. I will have to investigate this further.
Where on these pictures is the vertical lock circuit located?

Ive added some pictures of the full system if you or anyone else is interested. Its one of my favourites and is in excellent condition in every way for its age. Doesn't even use windows. It uses GEM desktop (graphical environment manager). The monitor is also well made and can give monocrome, Amber & colour displays.

[stj]

Re: CRT colour monitor Screen intermittant jumping

no idea on vertical - just search the part numbers on the chips.
interesting monitor - i never saw one with the focus and screen controls sticking out.

[R_J]

Re: CRT colour monitor Screen intermittant jumping

The vertical output ic is the one under the square silver heatsink in 1.jpg when you say text was shrinking do you mean vertcally (top to botom) or horzontally,(squeezing in from the sides). try poking around with an insulated stick (chopstick) and see if you can make it act up.
You could resolder the 100ohm resistor, They are higher wattage resistors so the do get hot and over time can cause the solder on them to fail.