Philips TV unable to tune channels after repair attempt

[TheNic]

Hello,
I have a Philips 12TX3501 BW PAL TV (AC/DC) with TX3 chassis (https://elektrotanya.com/philips_tx3.pdf/download.html), and it had a strange intermittent contact issue. I resoldered many joints until I discovered a broken grounding trace on top of the flyback transformer that I fixed. I also cleaned all the potentiometers using a gentle contact spray (Teslanol T6).

After this repair attempt, I’m now barely able to tune in the channel from an HDMI to-RF converter (used for testing) which wasn’t an issue before. The picture is now rolling vertically from top to bottom.

I’m completely new to repairing CRT TVs and I only know the basics (like how to discharge the tube). Unfortunately, I accidentally blew the fuse while probing the area around TS421 with my ESD gloves.

I did several measurements using my MiniDSO, and the signals on pins 18, 21, and 23 all seem fine.
Where could this issue be coming from?

Here is a video of the TV's behaviour: https://youtu.be/PUL0uatmhak?feature=shared

Any ideas would be greatly appreciated.
Thank you very much!
Nico

[vol.2]

Is there a vertical hold adjustment on the set? Did you adjust it?

[zeno]

Originally Posted by vol.2

Is there a vertical hold adjustment on the set? Did you adjust it?

Ditto No vert sync. try hold first

73 Zeno
LFOD !

[TheNic]

Thank you, vol.2 and zeno!
Since I ever never proper knowlege nor equipment for adjusting the circuitry, I didn't move the pots inside the housing on purpose.

Is the V sync hold circuit the one that is adjusted with R 406?
(Have to check when I'm at home.)
I will measure it's resistance and note it for the case I have to revert the change.

[Dude111]

I hope she is able to be fixed


Nice to see you posting...

[vol.2]

Originally Posted by TheNic

Is the V sync hold circuit the one that is adjusted with R 406?

It sort of looks like they are trying to say that is the V hold adjustment based on the little graphic of the screen rolling.

Typically, the V-hold is labelled on the plastic case from the outside of the TV. On older sets, it was a very common adjustment that was user controllable, not a service adjustment.

In any case, I have never seen a TV where the vertical hold adjustment was not labelled somewhere, either on the PCB or the case.

[TheNic]

Thank you very much!
At least this did work. I remembered this externally exposed pot as for adjusting the height of the image or something like that. But it can actually be used to stabilize the vertical signal!

However, my main problem seems to be that I’m only receivingthe signal very weakly. It even seems like the channel indicator is still kinda breaking through. I’ve now tried it with a VHS recorder to rule out an error with the HDMI-to-RF converter, even though that works on another TV. It’s puzzling.

(Sorry for vertical video syndrome but it was the most efficient way to bring both into the same view.)

https://drive.google.com/file/d/1g8L...w?usp=drivesdk

[vol.2]

Originally Posted by TheNic

I remembered this externally exposed pot as for adjusting the height of the image or something like that. But it can actually be used to stabilize the vertical signal!

Vertical Size adjustment can have an impact on the vertical hold as well, so you have to look carefully at how the pots are labelled. If it says "vertical size" then it's vertical size. You need to find the "vertical hold" adjustment, which is often times on the rear of the set (but not always for sure).

If you are sure you're making the correct adjustments, then you might need to adjust the fine tuning on the channel selector if you haven't done that yet. The image you showed in your video looks like it might just be slightly out of tune or something.

If it's something more serious, I can't help you as I'm not very good at RF stages. Someone else here would need to comment.