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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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CRT monitor repair
I have this Commodore 1950-B multisync monitor. It is a rebranded
AOCCM314 monitor. http://www.monitorworld.com/Monitors...0aoccm314.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!) |
#3
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CRT monitor repair
On Jan 14, 11:24 pm, Sjouke Burry
wrote: wrote: I have this Commodore 1950-B multisync monitor. It is a rebranded AOCCM314 monitor. http://www.monitorworld.com/Monitors...0aoccm314.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? 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. |
#4
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CRT monitor repair
schreef in bericht ... I have this Commodore 1950-B multisync monitor. It is a rebranded AOCCM314 monitor. http://www.monitorworld.com/Monitors...0aoccm314.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 |
#5
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CRT monitor repair
"petrus bitbyter" schreef in bericht l.nl... schreef in bericht ... I have this Commodore 1950-B multisync monitor. It is a rebranded AOCCM314 monitor. http://www.monitorworld.com/Monitors...0aoccm314.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 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 |
#6
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CRT monitor repair
"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 |
#7
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CRT monitor repair
On Jan 15, 3:27*am, "Phil Allison" 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 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. |
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