Sony 1953MD pvm ghosting issues with possibly 75ohm auto termination

[HermanMunster]

Hi there! I have fully recapped my 1998 Sony PVM model 1953MD. Before the recap I noticed some video ghosting issues when there was a dark screen and a bright image in the middle. After the full recap, the ghosting issue is still there. I am connecting my console through tbe rgb input and have tried different consoles all showing the same issue (the problem is not coming from the consoles; I have another PVM and it doesn't show the ghosting issue).

Could it be that the auto 75ohm termination is broken? There is a squiggly line right next to the out bnc conectors which means that they should all be auto terminated. How can I test that they are indeed 75ohm terminated?

Could this be an issue with a setting in the service menu? I tried modifying the color brightness and contrast, but the issue is still there.

I would greatly appreciate any advice!

[HermanMunster]

I tested 76 ohms in each one of the rgb and sync video lines with ground, so the 75ohm terminations are working properly. Any other ideas as to what might be causing the issue?

[jd213]

Could be some other component, maybe check voltage regulators since those can be easily tested with a multimeter.

I've also seen people report that some resistors (like the ones on the neckboard) can go bad without completely failing, so maybe desolder one leg of some of those and check them.

[HermanMunster]

Thanks for your reply! That is a good start. Do you know specifically which resistors and/or voltage regulators should I test? which ones control the brightness and contrast? There arent really that many on the neck board so I could just desolder them all I guess.

Another thing that I noted yesterday is that the issue worsens the longer the tv is turned on. At first it is barely noticeable, but the longer it stays on, the worse the issue becomes.

[jd213]

I couldn't say personally as I'm not good at deciphering schematics, but there shouldn't be too many voltage regulators at least.
Maybe check if any of the transistors have any shorts, but I'm guessing that would cause more noticeable issues.

[HermanMunster]

Thanks again for your reply. Here is a picture of the issue:
<a href="https://ibb.co/mtjyRRH"><img src="https://i.ibb.co/mtjyRRH/20231014-001941.jpg" alt="20231014-001941" border="0"></a>

If you are unable to see it, just zoom into the right side of the letters and you'll be able to see it. Ghosting only appears to the right of brighter objects for some reason.

I was hoping that a solution to this problem for this specific pvm model already exists since I've read on this and other forums older posts from people having the same issue. None of those posts had a permanent solution to the problem. One stated that it was an electrolytic capacitor problem, but mine is clearly not, since I have already replaced all of them.

[HermanMunster]

Here are better pictures of the issue:

https://ibb.co/mtjyRRH
https://ibb.co/LCPD4W0
https://ibb.co/HND3Zwx

[BazookaBen]

A guy on r/crtgaming posted a foolproof way to troubleshoot streaking but it requires an oscilliscope:

https://www.reddit.com/r/crtgaming/comm ... t/k3vazpc/

Spoiler

I have posted multiple times in the past, examples where I added a DC clamp to CRT TVs that do not have one. It used to be common for CRT TVs to not have a DC clamp for the keeping a consistent black level. Video quality is dramatically improved when the video signal has a DC clamp aka “DC restoration” aka “DC reinsertion” aka “brightness clamp” circuit.

In my experience, when the DC clamper isn’t working correctly, you can get that visual defect. The reason is that the black segment of video signal for those lines has a higher average voltage (for negative polarity video signal). So the video signal will drift up if the clamper isn’t working correctly, and when amplified the signal is inverted at the cathodes. So the at the cathodes the a lower average voltage is used, causing the brightness to be too high.

Depending on the clamper circuit, a resistor, capacitor, diode, or IC is faulty.

I am guessing that this is the issue based off of a picture and would need to oscope the circuit to confirm. It could also be a resistor or capacitor that have drifted in value in the video signal path, causing the RC time constant for that part of the signal path to be too high.

[HermanMunster]

Thank you! The oscilloscope testing sounds like a fun project to get into. But first of all, what is a DC clamp and how do I get one? Also, what oscilloscope do you recommend for this? I think it is time for me to get an oscilloscope, but wouldn't like to spend more than $250 on it if possible.

[BazookaBen]

Thank you! The oscilloscope testing sounds like a fun project to get into. But first of all, what is a DC clamp and how do I get one? Also, what oscilloscope do you recommend for this? I think it is time for me to get an oscilloscope, but wouldn't like to spend more than $250 on it if possible.

Lol I dunno, I'm just reposting what I read. I just have a couple TVs with the issue so I plan to give it a try one day

[HermanMunster]

I saw this really good posting about calibrating the crt brightnesa here: viewtopic.php?t=67477

Do you think that my problem could be solved with any of the adjustments mentioned in this post? When I tried to adjust the brightness through the front panel controls it did not make the problem any better or worse.