CRT monitor repair

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

http://www.monitorworld.com/Monitors/commodore/1950aoccm314.html

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!)
 
a7yvm109gf5d1@netzero.com wrote:
I have this Commodore 1950-B multisync monitor. It is a rebranded
AOCCM314 monitor.

http://www.monitorworld.com/Monitors/commodore/1950aoccm314.html

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!)
Click to expand...
Power transistors in the deflection steering degrading?
Or supply voltages around that area unstable?
 
On Jan 14, 11:24 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnll>
wrote:
a7yvm109gf...@netzero.com wrote:
I have this Commodore 1950-B multisync monitor. It is a rebranded
AOCCM314 monitor.

http://www.monitorworld.com/Monitors/commodore/1950aoccm314.html

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!)

Power transistors in the deflection steering degrading?
Or supply voltages around that area unstable?
Click to expand...
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.
 
<a7yvm109gf5d1@netzero.com> schreef in bericht
news:be38503d-2424-4ad4-a152-576504419e02@26g2000yqo.googlegroups.com...
I have this Commodore 1950-B multisync monitor. It is a rebranded
AOCCM314 monitor.

http://www.monitorworld.com/Monitors/commodore/1950aoccm314.html

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!)
Click to expand...

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
 
"petrus bitbyter" <pieterkraltlaatditweg@enditookhccnet.nl> schreef in
bericht news:4b502909$0$7027$e4fe514c@dreader32.news.xs4all.nl...
a7yvm109gf5d1@netzero.com> schreef in bericht
news:be38503d-2424-4ad4-a152-576504419e02@26g2000yqo.googlegroups.com...
I have this Commodore 1950-B multisync monitor. It is a rebranded
AOCCM314 monitor.

http://www.monitorworld.com/Monitors/commodore/1950aoccm314.html

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!)


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
Click to expand...
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:
http://www.repairfaq.org/sam/monfaq.htm#monwdflyd

petrus bitbyter
 
"petrus bitbyter"

Looks like a collapsing EHT.
Click to expand...
** 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
 
On Jan 15, 3:27 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"petrus bitbyter"



Looks like a collapsing EHT.

** 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
Click to expand...
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.
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top