Author Topic: panasonic tx-21md1c lines even worse after recap  (Read 405 times)

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Offline tonimajmun2001

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panasonic tx-21md1c lines even worse after recap
« on: January 24, 2020, 08:57:17 pm »
So this is my first time working on a CRT (yes i do know how to safley discharge them :) )

Uncle has old panasonic crt that has some lines at the top of screen (look similar to retrace lines) and few RGB blinking lines at the middle of the screen and since i have expierence recaping old radios and amps he decided to let me try to fix it

Now i didnt even look at the service manual cause i hear many times that stuff like lines on CRTs can often be fixed by simple recap, i diecided for now to replace only the caps that i have spares for and if that fixes it great and if it stays the same then i would order other caps too

Before recap picture was perfect (contrast, broghtness and colors all perfect) besides issue with lines but now after recap everything is 100x worse, there are lines all over the screen now but are thinner than ones that were already on the top part of screen, brightenss seems wrong and high and colors are all washed out and weak and contrast is literally CRAP, settings menu for example had nice deep blue background but now after recap that blue is all washed out, here is the video showing how it looks after recap, i used old PS2 as signal source in this video (sorry for bad English in video)

Did i somehow destroy something permanently on this CRT?


I know it might be easiest to give it to someone who repairs to crt to fix it but its my first time repairing a crt and i want to try and learn to fix this one so any help is appriciated

Also one probably stupid question, since screen seems bright can it cause TV to emit some radiation, should i be worried or would it turn off to protect against radiation?

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

Any help is appriciated :)
« Last Edit: January 24, 2020, 09:01:15 pm by tonimajmun2001 »
 

Offline mzacharias

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Re: panasonic tx-21md1c lines even worse after recap
« Reply #1 on: January 25, 2020, 01:15:47 am »
Looks like a bad boost capacitor associated with the vertical output IC, something like 100uF at 35V, or a bad cap off a flyback derived supply, such as 10uF at 160V, near the flyback transformer.
 

Offline tonimajmun2001

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Re: panasonic tx-21md1c lines even worse after recap
« Reply #2 on: January 25, 2020, 01:33:07 am »
Looks like a bad boost capacitor associated with the vertical output IC, something like 100uF at 35V, or a bad cap off a flyback derived supply, such as 10uF at 160V, near the flyback transformer.

Thanks, i will check tomorrow (its 2:30am in my timezone right now) if i already replaced those caps

Btw, any ideas why it would get that much worse after i recaped part of the board, before recap everything was fine except a few lines at the top of screen then after recap it turned into a disaster that you can see in the video i posted
 

Offline shakalnokturn

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Re: panasonic tx-21md1c lines even worse after recap
« Reply #3 on: January 27, 2020, 09:29:57 am »
Are the flicker and black strips actually visible or is that just an artifact from filming the TV?

Things wouldn't usually get much worse by changing the capacitors unless you have made a mistake on the way such as getting the wrong value or making a short with a solder bridge.
Other possibilities are dry solders (have you checked for that? Don't forget CRT board.) that could have finished loosening while you handled the PCB, bad interconnect, readjustments that had been previously made to compensate for brightness problems due to ageing capacitors.

The part I don't get in your original fault description is the "RGB blinking lines", did the picture show vertical distortion or foldback originally?
 

Offline TERRA Operative

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Re: panasonic tx-21md1c lines even worse after recap
« Reply #4 on: January 27, 2020, 01:29:12 pm »
Are you 100% sure you replaced the capacitors with same values, and good quality brands?

Also, I have found that often there is a bipolar capacitor there somewhere too, so be sure to use a new bipolar cap.

Also, also, have you given the dials a tweak? Sometimes the TV will need the sync hold dials etc readjusted after the old caps are replaced to compensate for the fresh new parts.
« Last Edit: January 27, 2020, 01:33:01 pm by TERRA Operative »
Any circuit design must contain at least one part which is obsolete, two parts which are unobtainable, and three parts which are still under development.

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