Help Fixing Television

[Scrim]

I'm experienced with electronics but don't know much about TV's. Can anyone
help me identify this problem?

Panasonic TX-W28R4
Recently: After switching on from cold every now and then the picture starts
to shrink in the vertical direction. I bang the top a few times over a space
of 15 minutes each time this happens after which it's warmed up and works
fine. Sometimes the picture shrinks to the bottom inch or two of the screen
and is scrambled. Occasionally the screen goes blank and the TV shortly
afterwards shuts itself off.

I lived with that but now the problem is worse. A few seconds after
switching on and nothing appearing to happen, there is a flash on the screen
of light collapsing towards the centre as the TV shuts off. I can't use it
at all any more.

I vacuumed the circuit boards free of dust and this gave me two more days.
I just tried pulling/reinserted all the connectors but that hasn't helped.

Any ideas gratefully received.

Scrim

 

[Samuel M. Goldwasser]

Sounds like a flakey cap in the vertical section or power supply. Look
for a bulged/discolored electrolytic cap or one that appears to have
'leaked' around it's base.

He said banging on the top and it changes. Most like a cracked solder
joint. May even be at the vertical yoke connector.

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[Arfa Daily]

I'm experienced with electronics but don't know much about TV's. Can
anyone help me identify this problem?

Panasonic TX-W28R4
Recently: After switching on from cold every now and then the picture
starts to shrink in the vertical direction. I bang the top a few times
over a space of 15 minutes each time this happens after which it's warmed
up and works fine. Sometimes the picture shrinks to the bottom inch or two
of the screen and is scrambled. Occasionally the screen goes blank and the
TV shortly afterwards shuts itself off.

I lived with that but now the problem is worse. A few seconds after
switching on and nothing appearing to happen, there is a flash on the
screen of light collapsing towards the centre as the TV shuts off. I can't
use it at all any more.

I vacuumed the circuit boards free of dust and this gave me two more days.
I just tried pulling/reinserted all the connectors but that hasn't helped.

Any ideas gratefully received.

Scrim

Bad joints on the field output chip. Very common on Pans of a few years old.
Fix it now before the IC fails from all the arcing and flashing about on its
pins, or the board starts to burn up around the bad joint. Even if you can't
actually see anything that looks like a bad joint on any of the pins, reflow
them with some new solder anyway.

Arfa

 

[Kevin Dooks]

I'm experienced with electronics but don't know much about TV's. Can anyone
help me identify this problem?

Panasonic TX-W28R4
Recently: After switching on from cold every now and then the picture starts
to shrink in the vertical direction. I bang the top a few times over a space
of 15 minutes each time this happens after which it's warmed up and works
fine. Sometimes the picture shrinks to the bottom inch or two of the screen
and is scrambled. Occasionally the screen goes blank and the TV shortly
afterwards shuts itself off.

I lived with that but now the problem is worse. A few seconds after
switching on and nothing appearing to happen, there is a flash on the screen
of light collapsing towards the centre as the TV shuts off. I can't use it
at all any more.

I vacuumed the circuit boards free of dust and this gave me two more days.
I just tried pulling/reinserted all the connectors but that hasn't helped.

Any ideas gratefully received.

Scrim

Sounds like a flakey cap in the vertical section or power supply. Look
for a bulged/discolored electrolytic cap or one that appears to have
'leaked' around it's base.

Hope this helps

Kevin

 

[PainintheAmp]

I'm experienced with electronics but don't know much about TV's. Can anyone
help me identify this problem?

Panasonic TX-W28R4
Recently: After switching on from cold every now and then the picture starts
to shrink in the vertical direction. I bang the top a few times over a space
of 15 minutes each time this happens after which it's warmed up and works
fine. Sometimes the picture shrinks to the bottom inch or two of the screen
and is scrambled. Occasionally the screen goes blank and the TV shortly
afterwards shuts itself off.

I lived with that but now the problem is worse. A few seconds after
switching on and nothing appearing to happen, there is a flash on the screen
of light collapsing towards the centre as the TV shuts off. I can't use it
at all any more.

I vacuumed the circuit boards free of dust and this gave me two more days..
I just tried pulling/reinserted all the connectors but that hasn't helped..

Any ideas gratefully received.

Scrim

I agree with the other techies.
Resolder the chip mentioned and the horizontal output transistor(the
area near it too)

 

[Scrim]

Arfa, You're a diamond geezer! Cheers!
I found the service manual online, identified the 'field output chip' as :
IC451 LA7845N VERTICAL OUTPUT (Sanyo call it a 'Vertical Deflection Output
Circuit')
a 7 pin SIP7H package on the main pcb. Soldered all the pins as you
suggested (a pin at one end was hard to get the solder to flow on despite
using lots of flux, so I guess it was badly oxidized from arcing and was the
problem), and the TV's now 100% working
Three days without telly, I was starting to get the shakes!
Thanks again,

Scrim

 

[Arfa Daily]

Arfa, You're a diamond geezer! Cheers!
I found the service manual online, identified the 'field output chip' as :
IC451 LA7845N VERTICAL OUTPUT (Sanyo call it a 'Vertical Deflection
Output Circuit')
a 7 pin SIP7H package on the main pcb. Soldered all the pins as you
suggested (a pin at one end was hard to get the solder to flow on despite
using lots of flux, so I guess it was badly oxidized from arcing and was
the problem), and the TV's now 100% working
Three days without telly, I was starting to get the shakes!
Thanks again,

Scrim

Glad to have been of help.

Arfa

 

[Scrim]

I love the internet

Scrim

Glad to have been of help.

Arfa

 

[Arfa Daily]

I love the internet

Scrim

Good, innit ? Just one thing if you're new to Usenet newsgroups. It's normal
'protocol' to bottom post rather than top, as you would do with e-mail. It
helps the thread to 'flow' chronologically a bit better, for readers who
join it late. Also makes it easier to trim a post that you are replying to,
without compromising the overall flow of the thread. Won't win you any
trouble on this group, but on some, they are really picky, and will lay into
you for top posting. d;~}

Arfa