Panasonic CRT horizontal lines even worse after recap

Thread Starter

tonimajmun2001

Joined Jan 24, 2020
10
Hi, so i usually recap old radios (including tube radios) and recently i decided for a change to recap old panasonic CRT TV (model tx-21md1c) that had horizontal lines on tophalf of the screen with blinking red green and blue lines in the middle of the screen

So for now i replaced only the caps that i had in stock hoping that it would at least make it better but somehow after recaping everything is now 100x worse and now lines are all over the screen (new lines are thinner while lines that were there before recap are thicker and still there)

So before recap aside from lines picture was perfect, contrast brightness and color were all pefrect but now after recap screen is all washed out, there are no more black colors screen is very white and bright and contrast is literally the worst i have ever seen and lines are now all over the screen

So basicly TV went from very usable even tough it had lines to completley unusable

here is a video where you can see how it looks now after recap, the singal source used in the video was old ps2 connected to composite input (i love retro consoles):

and here is a list of all caps that i have replaces so far
C361
C563
C703
C450
C462
C455
C701
C852
C862
C856
C853
C509
C860
C7224
C806
C807
C804
C811

I really want to try to fix this thing so any help is appriciated and i am very willing to learn how to diagonose CRTs (i know how to safley discharge them and i am comfortable working with high voltages:) )
 
Last edited:

DickCappels

Joined Aug 21, 2008
6,301
With the information presented, it would be difficult to diagnose the problem. Since the retrace lines are visible, I my first action would be to adjust the G2 voltage (cutoff voltage adjustment). The pot for his is usually mounted on the flyback transformer assembly along with the focus voltage pot.

Be very careful because while everything should be well insulated, it is still high voltage and conductors that are not grounded can charge up to a high potential.
 

ronsimpson

Joined Oct 7, 2019
606
It is hard to know, but it looks like the vertical retrace is very slow. Some sets blank the screen while vertical is retracing. There should be a boost cap in the vertical amp. If that is not working right …… If I could see a scope picture if the voltage on the hot end of the vertical yoke ….

I don't know your set but here is a typical vertical amplifier. If the cap from pin 2 to 11 is bad, 1n4001 is bad or the IC is bad at pin 2,11 the retrace will be slow. I often used the "V. flyback generator" to blank the picture. If the vertical amp is working right the voltage at pin-1 should extend upward to almost twice +Vs (during vertical retrace).
1579927250447.png
 

Thread Starter

tonimajmun2001

Joined Jan 24, 2020
10
What leads you to believe that capacitors have anything to do with the appearance of scan lines.
The scanlines and awful picture you see now in the video i posted started hapening after i a recap before it was more like this (found this examples on google)
crt1.jpg
crt2.jpg

and ive seen many people get rid of this lines at the top of the screen by replacing filter caps on the chassis but only now AFTER replacing them i have scanlines all over the screen like you can see in video on my first post so it seems like it is a seperate issue that appeared after recap

With the information presented, it would be difficult to diagnose the problem. Since the retrace lines are visible, I my first action would be to adjust the G2 voltage (cutoff voltage adjustment). The pot for his is usually mounted on the flyback transformer assembly along with the focus voltage pot.

Be very careful because while everything should be well insulated, it is still high voltage and conductors that are not grounded can charge up to a high potential.
Thanks, i will try adjusting G2 voltage today but i am sure i didnt touch that pot while recaping and it was fine before recap, and there were only few lines on top of the screen but now after recap lines are all over the screen and picture quality overall is completley messed up

If you need more info just let me know what you need and i will try to provide information

It is hard to know, but it looks like the vertical retrace is very slow. Some sets blank the screen while vertical is retracing. There should be a boost cap in the vertical amp. If that is not working right …… If I could see a scope picture if the voltage on the hot end of the vertical yoke ….

I don't know your set but here is a typical vertical amplifier. If the cap from pin 2 to 11 is bad, 1n4001 is bad or the IC is bad at pin 2,11 the retrace will be slow. I often used the "V. flyback generator" to blank the picture. If the vertical amp is working right the voltage at pin-1 should extend upward to almost twice +Vs (during vertical retrace).
View attachment 197573
Thanks, i think i already replaced the caps you mentioned, unfortunatley i only have multimeter and i have no scop so my options for measuring are limited...

The only thing that i am 100% sure is that the problem you see in the video i posted appeared AFTER i have done recap on the board, before this only few lines were appearing on top of the screen and now after recap scanlines are visible all over the screen and picture quality is awful

I really dont know how replacing capacitors caused even more problems than it fixed unless i fried something but i didnt touch anything besides caps... :(
 

Papabravo

Joined Feb 24, 2006
13,461
I believe you. My point was that, without a schematic and a deep understanding of the circuit, just replacing capacitors is not likely IMHO to fix the problem and could possibly make things worse for reasons that remain obscure. Most adjustments inside a TV chassis involve potentiometers which can age and degrade just like capacitors. In a new TV you can get scan lines to appear by making extreme settings of brightness and contrast.
 

Thread Starter

tonimajmun2001

Joined Jan 24, 2020
10
Update: so i now tried adjsuting screen voltage pot on flyback (huge thanks to all of you who recommended to try this first :) ) and now picture is finally back to how it was before recap, color and everything is now normal and retrace lines dissapeared and now i am left with only lines that were on top of the screen before recap and blinking RGB lines so now im only left with the problem that i was trying to fix in first place

This is how it looks now that G2 voltage is correct and this is a picture of the problem i was trying to fix in the first place:20200125_140014.jpg

And here is a short video showing it:

It looks like the lines that are showing at the top of the screen should actually be drawn higher up because it looks like there is part of the screen completley black at the top (clearly visible in video)
 

Thread Starter

tonimajmun2001

Joined Jan 24, 2020
10
I believe you. My point was that, without a schematic and a deep understanding of the circuit, just replacing capacitors is not likely IMHO to fix the problem and could possibly make things worse for reasons that remain obscure. Most adjustments inside a TV chassis involve potentiometers which can age and degrade just like capacitors. In a new TV you can get scan lines to appear by making extreme settings of brightness and contrast.
I have managed to find service manual, i will try looking at the schematics soon

Here is the PDF of the service manual in case anyone wants to look at it

EDIT: i seem to have found one more service manual for this model that has more pages, i have attached that PDF now too
 

Attachments

Thread Starter

tonimajmun2001

Joined Jan 24, 2020
10
Looking at schematics it looks like that IC451 (TDA8175) is responisble for vertical output, i will later check if its getting proper voltage and double check that i replaced all caps that circut and if everything else looks fine could it be that this IC is dead?
 

abrsvc

Joined Jun 16, 2018
32
What you are seeing is a fairly common failure of the vertical circuit that is resolved either by replacing the vertical IC (TDA8175) and or the electrolytic capacitors in the vertical circuit. Check/replace C460 and C456. Look for any cap that is 50-100ufd with a 3xx designation that is in the general area and check those too.

That should resolve the problem.

Dan
 

Thread Starter

tonimajmun2001

Joined Jan 24, 2020
10
What you are seeing is a fairly common failure of the vertical circuit that is resolved either by replacing the vertical IC (TDA8175) and or the electrolytic capacitors in the vertical circuit. Check/replace C460 and C456. Look for any cap that is 50-100ufd with a 3xx designation that is in the general area and check those too.

That should resolve the problem.

Dan
Thanks, i will check it
 

Thread Starter

tonimajmun2001

Joined Jan 24, 2020
10
Sorry for the lack of updates on this, due to personal issues i havent had time to take a look at it again but hopefully i will be able to in the next few days
 

Thread Starter

tonimajmun2001

Joined Jan 24, 2020
10
I noticed the top of the picture is folded over. D453 & C454 (D454,456 probably are ok)
Maybe C462 is too small.
View attachment 197595
Finally had some time to look at it again and seems like on this model D453 is nonexistant, on PCB where D453 is marked there is only a jumper and D453 is not even in service manual parts list.

IMG_20200208_161605.jpg



C454 is SMD cap 50v 100nF but i will have to order these cause i dont have any at the moment.

C462 i already replaced with value that is written in service manual (35v 3300uF).
 

Thread Starter

tonimajmun2001

Joined Jan 24, 2020
10
What you are seeing is a fairly common failure of the vertical circuit that is resolved either by replacing the vertical IC (TDA8175) and or the electrolytic capacitors in the vertical circuit. Check/replace C460 and C456. Look for any cap that is 50-100ufd with a 3xx designation that is in the general area and check those too.

That should resolve the problem.

Dan
I will try replacing C460 but its another one i first have to order cause i dont any in stock unfortunatley, according to service manual its film cap

C456 is already replaced, i just forgot to write it down on the list of replaced ones :)

I will leave replacing IC as a last option if nothing else fixes it, lets hope that replacing that film cap that you mentioned and one SMD cap that ronsimpson mentioned will help :)
 

abrsvc

Joined Jun 16, 2018
32
If you have a cap of the correct value, you can tack it in place for testing while waiting for the SMD one. Might save you a bit of time if the cap won't fix the problem.
 
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