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pcdata76
May 27th, 2017, 03:46 AM
Hello,

Last week i've recovered a beautiful Sony trinitron CPD-1301E CGA monitor produced in mid 80's (it can do both TTL RGB/RGBI and analog 15 kHz RGB) from a computer junkyard. There was some small scratches on its front bezel otherwise it was in a quite a good physical condition so i've picked it up.

After a short story, now it comes to the problem. Monitor powers on, displays a picture in correct geometry but even and odd lines are misaligned as you can see from the picture below in 80% of the entire screen. Even lines and odd lines are aligned within themselves but not with eachother. Only center-left part of the screen is in correct alignment.

https://www.dropbox.com/s/e0nuxbrwsvd88tx/CPD1301E.jpg?dl=0


I've repaired numerous CRT monitors and TV's before but i didn't meet such a strange problem ever. Unfortunately, i can't source the service manual/scheamtic of this beauty anywhere and this makes the things much worse. The nearest model which i can find its manual is CPD-1402 model but it is a multisync (CGA-EGA-VGA) monitor and has a very different (and more complex as expected) circuit and nothing common with mine.

I've opened the case of the monitor and verified that none of the adjustable controls are affecting to the problem. There are no any burn marks on the components, darkening on the PCB due to heat or any bulged capacitor. Internals of the monitor is also very clean, has the least amount of dust which i've ever seen in a CRT. It seems that th unit has very low hours because tube is also looking quite decent (good brightness and colors, perfect focus). Monitor also has a dynamic convergence alignment circuit and totally lacks the usual rotary convergence alignment magnets on its yoke. Instead, there is a coil which is connected to a part of the circuit having electrical convergence adjustment potentiometers on it. In addition to the difficulty of getting a working CGA/EGA monitor in my country, i really want to put this monitor in operation for these reasons. It will be also my first CGA monitor if i can repair.

Since it is more than 30 years old, electrolytic capacitors are looking me first to suspect. I'm planning to remove and measure each possible cap using ESR meter if i can't get any info to narrow down the fault.

PS: I've operated the monitor using different CGA cards and problem didn't changed at all. It also doesn't change in analog mode too. Leaving it operating for an hour is also changes nothing.

Thank you for your help,

pcdata76
June 3rd, 2017, 11:04 AM
Solved. As a future reference: Problem was the wrong horizontal oscillator frequency which is needed to be adjusted precisely from RV505 potentiometer on the BA board. In my case, potentiometer had jittery contacts and i've replaced it with a multi turn potentiometer for more precise adjustment. I've adjusted it until all even and odd lines are aligned throughout the screen.

Note: After HFREQ adjustment, monitor was getting difficulty to lock horizontal sync or couldn't sync at all after a cold start. I've solved it by tweaking horizontal pulse width potentiometer (RV309 on BA board). After some more fine tuning (convergence, geometry etc.) monitor is now working great!

PS- During the troubleshooting process, i've removed and measured some of the caps (especially the ones in the horizontal part) and they were all totally good and still had lower ESR than new chinese caps which i've measured as a comparison ;) Impressive result in favor of the 30 years old japanese caps!