CRT monitor repair

I have this Commodore 1950-B multisync monitor. It is a rebranded AOCCM314 monitor.

formatting link

A bit atypical of the era, it could sync from 15KHz-35KHz continuously (no click-clunk relays selecting caps), and 50-80Hz vertically.

I haven't worked on monitors in ages, but I am competent enough to figure it out slowly. Just need some pointers.

The symptom it displays is that the picture only displays when the horizontal position is at the extremes, left or right. As I try to center it, the picture goes dim and eventually fades to black.

Does this sound familiar? I'm gonna look at the overall DC supplies first, then look at the CRT grid and cathode drives. What would you check next?

I'm still trying to track down the schematics, but the monitor is much more complex than a fixed frequency RGB job.

I want to think about this before commiting to a repair in my limited space. (CRTs are big!)

Reply to
a7yvm109gf5d1
Loading thread data ...

Power transistors in the deflection steering degrading? Or supply voltages around that area unstable?

Reply to
Sjouke Burry

I don't know... For all I know, the filament voltage goes up and down. Haven't measured anything yet. It's a project that will start in a few days.

Reply to
a7yvm109gf5d1

schreef in bericht news: snipped-for-privacy@26g2000yqo.googlegroups.com...

Looks like a collapsing EHT. As EHT is made by the horizontal deflection unit, the EHT stack, the HOT and the driving transistor are prime suspects. Usually the filament is also powered by the HOT.

petrus bitbyter

Reply to
petrus bitbyter

"petrus bitbyter" schreef in bericht news:4b502909$0$7027$ snipped-for-privacy@dreader32.news.xs4all.nl...

Oops. The HOT is the Horizontal Output Transistor so the driving transistor mentioned above and *not* the horizontal output transformer. The latter is called LOPT or Line OutPut Transformer. See also:

formatting link

petrus bitbyter

Reply to
petrus bitbyter

"petrus bitbyter"

** Very unlikely.

My CRT monitor goes almost back if the image is pushed as far as possible to the right using the on-screen adjustments.

Works perfectly in every other way - so is not a fault at all.

.... Phil

Reply to
Phil Allison

to

It sounds like a problem with the horizontal centering control if the OP described things correctly. I would clip lead all three leads to the pot together and see if the picture was reasonably centered, and if so would then see about replacing the pot.

Reply to
hrhofmann

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.