Vertical deflection problem 7 inch chinese CRT TV

[VU3KFK]

Hi all,

I am requesting your help, I have a 7 inch Chinese portable B&W CRT television that runs on 12V. Vertical deflection is very unstable. Picture is distorted. I am completely new to this television related electronics. I am a radio amateur and i have knowledge of radio circuits, but very little on TV circuits. This TV is controlled by single IC named CD5151CP, which is also known as KA2915, made by some Chinese company. The most surprising thing that I found is there are two LM386 IC on board. One is for audio output another is for Vertical deflection amplifier. For audio the IC is named as YD386 and for vertical deflection amplifier it is D386 and D386 is getting warmer. I have taken pictures of the circuit board and made a drawing of the vertical deflection circuit having D386, also created a video of the screen, uploaded datasheet of 5151 IC, which also have a application circuit. I have stored all of these in my google drive linked below. For any further information please let me know. I will share.

https://drive.google.com/drive/folde...Wm?usp=sharing

[jhalphen]

Hi to all,
Hi VU3KFK, Welcome ! to the TV Repair section

Your Google Drive photos show you have some sort of full screen vertical & horizontal scan (a raster) so something is working.

Are you applying a video signal to the TV, if so, how?
Via a VHF modulator with Channel 3 or 4 output connected to the TV's antenna ?

or

Via a direct composite video baseband signal to the TV's monitor input (if it has one) ?

Your photos do not show the full board so it's impossible to see if the TV has an A/V monitor input.

With no signal present, the H & V oscillators run unlocked so it's pretty normal to have the scan doing strange things.

The LM386 is an audio amp & vertical scan is basically a 60Hz amplifier so it's not unusual to see one there.

The chassis would benefit from a cleanup (Kleenex & Q-Tips).
Look for any bulging electrolytic capacitors.

Please add photos with video content displayed.
You can post photos directly here bypassing Google Drive.

Best Regards
jhalphen
Paris/France

[ChrisW6ATV]

VU3KFK is in India, so maybe they still have analog TV signals in some places there?

[VU3KFK]

Thanks everyone for your comments. Yes I am from India, but the TV I collected for using with some Arduino TV interfacing project. Arduino will be connected to AV input of the TV. I do not have any plan to use it to receive from air.

When I took the picture, there was no signal applied.
I will not use RF connector and I will use AV input of the TV. It already have one. Currently I do not have an AV output device so I could not take pic with AV signal applied. I am working on that. But the person who gave it to me have shown me with AV signal and the screen is divided in 2 parts. The upper part shows the lower half of the picture and lower part of the screen shows upper half of the picture. And the picture is fluctuating.

I will update with better photos with signal applied.

[Electronic M]

Sounds like vertical hold control needs adjustment... you'll need a video source connected to set it.