Sony Trinitron CRT TV with dark spots on the screen

Dear Sirs,

Does your guide include information about this kind of Sony Trinitron?

CRT video problem as shown on the link below? Not sure where the

Problem is, but if you have the time could you please take a look a

Some screen pictures of the problem and more detailed description? 

 

I'm not really into commercial TV repairs, this is just for a one time fix of my personal set.

Thank you in advance.

Alex

  

Hi Alex,

First be sure there is not dry joints on the entire set starting from the

Small board at the back of the CRT neck and the main I.C. next adjust the focus knob a bit at the FBT body

Regards Humphrey

Hi Humphrey,

Thanks very much for contacting me. Yesterday I changed C701 a 10uF

250V mounted on the CRT board and that solved the problem.

The Capacitor had gone up in ESR to 28 ohms. I will retouch the focus adjustment as you suggest to see if that will further improve the Picture, although after changing C701 it already seems to have gotten 100% better, and the tears are almost entirely gone..

I still see some very-very slight faint right hand tearing across the screen from any bright white small spot if the screen is completely black, for example when the small turning "wait/loading" wheel from Netflix is shown in the middle of the black screen.

But I guess I can’t expect the video in a general consumer TV to be absolutely perfect as it is probably under those circumstances running into design 

limitations.Or am I wrong and further improvements are possible? I also checked Every other filter cap on the main board, but all where fine, so not sure anything further could be done. One thing I also noticed, probably something that happened a long time ago, is that C601, an AC  line bypass capacitor located right after the main AC fuse, is  partially burned up, and I can't see the value or voltage  specification on it, and neither are they specified in the service manual.

Any idea of the correct values for that capacitor? For the time being I just removed it. Thanks again for writing back.

Regards,

Alex

Hi Alex,

Thanks for your feedback and glad to hear the screen has now improved, yes capacitor failure can cause all manner of weird symptoms. 

The capacitor you picked is very critical because it filters the supply to RGB amplifier. 

But if the ESR was high means the line voltage was also low and therefore I could have expected the screen to have retrace lines and also very bright

Which you never mentioned in your observation, but still miracles do happen.

I tend to think that some of the symptoms you observed are also due aging tube.

For C601, I have not seen it one the circuit diagram but from what you said I think it has no big impact on the circuit.

Regards Humphrey