Best Source for TV Schematics??

[Jim Thompson]

The TV I bought for my office on 9/11/2001 has gone on the fritz...

Panasonic TC-15LT1

Warms up, then flicks back and forth between a perfectly good picture,
then totally washed out. Sound always stays good.

Who's the best source for a schematic? I'm leery of the Russian
sites, which seem to dominate this topic.

...Jim Thompson

 

[Joerg]

Hello Jim,

The TV I bought for my office on 9/11/2001 has gone on the fritz...

Panasonic TC-15LT1

Warms up, then flicks back and forth between a perfectly good picture,
then totally washed out. Sound always stays good.

Hey, since you kill bugs with freeze spray I guess it's time to try it
on the TV. It could be as simple as an electrolytic having become
marginal. Freeze spray is how I found out what caused our little PAL
standard TV to lose PLL lock. I really had to fix that one because we
can't buy them here and it's our sole source to watch old European tapes.

Who's the best source for a schematic? I'm leery of the Russian
sites, which seem to dominate this topic.

In the old days (meaning >20 years ago) I had good luck by writing
directly to the manufacturer. Nowadays many schematics are sold via
"service manual providers". Don't know what the fees are but a pdf
download shouldn't be too bad.

 

[Nico Coesel]

The TV I bought for my office on 9/11/2001 has gone on the fritz...

Panasonic TC-15LT1

Warms up, then flicks back and forth between a perfectly good picture,
then totally washed out. Sound always stays good.

Probably a defective electrolytic capacitor. Buy a can of freeze spray
too cool down components and start cooling down electrolytic caps near
heatsinks. I bet the culprit is close to the HV transformer.

Does slamming the TV help? If yes, check for loose soldering joints.

Who's the best source for a schematic? I'm leery of the Russian
sites, which seem to dominate this topic.

A schematic is not going to help. A basic understanding on how a TV
works and a not so expensive analog oscilloscope are more usefull.

 

[Jim Thompson]

Probably a defective electrolytic capacitor. Buy a can of freeze spray
too cool down components and start cooling down electrolytic caps near
heatsinks. I bet the culprit is close to the HV transformer.

HV? In an LCD flat-screen ?

Does slamming the TV help? If yes, check for loose soldering joints.

I have been known to completely re-solder a board... successfully ;-)

A schematic is not going to help. A basic understanding on how a TV
works and a not so expensive analog oscilloscope are more usefull.

Duh! I grew up in a radio/TV repair shop ;-)

Finding things on a dense board becomes problematic.

It has an external 15V/4A "power block". I'm beginning to be
suspicious of that.

...Jim Thompson

 

[Chuck Harris]

The TV I bought for my office on 9/11/2001 has gone on the fritz...

Panasonic TC-15LT1

Warms up, then flicks back and forth between a perfectly good picture,
then totally washed out. Sound always stays good.

Who's the best source for a schematic? I'm leery of the Russian
sites, which seem to dominate this topic.

There is no reason to be leery of the rusky sites. Get your schematic,
and move on.

Televisions are wonderful devices. When they fail, it is almost always
a bad solder joint, or a bad electrolytic. Some times there is some
collateral damage that results from the failure.

Get an ESR meter, and you can check all of the electrolytics quickly.

Freeze spray sometimes helps, but for intermittent, I usually use a fiberglass
stick, and tap here and there until I get a response. I found a bad solder
joint in a 25 year old sony just yesterday, that way.

-Chuck Harris

 

[Joerg]

Hello Jim,

HV? In an LCD flat-screen ?

Well, they generally do have a high voltage converter for the CCFL
tubes. Not tens of kV but a few kV. I don't know what you mean by
"washed out" though.

I have been known to completely re-solder a board... successfully ;-)

Same here. And certainly not with RoHS compliant solder. I can already
see myself resoldering RoHS stuff to get it back to non-RoHS performance.

Duh! I grew up in a radio/TV repair shop ;-)

Finding things on a dense board becomes problematic.

And figuring out what that highly unobtanium full-custom chip does that
reacted to the cold spray.

It has an external 15V/4A "power block". I'm beginning to be
suspicious of that.

Easy. Hook a digital scope to it and let it log the 15V in slow motion.
Or use a bench supply and see if the TV repeats the error.

 

[Jim Thompson]

Hello Jim,


Well, they generally do have a high voltage converter for the CCFL
tubes. Not tens of kV but a few kV. I don't know what you mean by
"washed out" though.

Loss of contrast.

Doesn't seem to (at least coherently) respond to "slamming".

Same here. And certainly not with RoHS compliant solder. I can already
see myself resoldering RoHS stuff to get it back to non-RoHS performance.

Bought this set the day of 9/11 so I could keep track of happenings
without leaving my desk... I was in the midst of a big project. So I
doubt if it was built to RoHS.

And figuring out what that highly unobtanium full-custom chip does that
reacted to the cold spray.

Natch. I probably should just go buy a new set and forget about it.
The replacement AC adapter alone is $126 :-(

Easy. Hook a digital scope to it and let it log the 15V in slow motion.
Or use a bench supply and see if the TV repeats the error.

Unloaded it's bouncing around. I'm going to rig up a "T" so I could
watch it while loaded.

I'd use a bench supply but, in my world, 4A is unheard of. All I have
is small supplies good to 300mA.

...Jim Thompson

 

[Bobo The Chimp]

The TV I bought for my office on 9/11/2001 has gone on the fritz...

Panasonic TC-15LT1

Warms up, then flicks back and forth between a perfectly good picture,
then totally washed out. Sound always stays good.

Who's the best source for a schematic? I'm leery of the Russian
sites, which seem to dominate this topic.

Your problem is easy to fix. Just open the back of the set, and
turn it on. (use a cheater cord if you have to.) Now, rest your left hand
securely on the chassis, and in your right hand, grasp a long-bladed
screwdriver. Using care to ensure that you are in contact with the metal
blade of the screwdriver, insert it decisively under the HV cap on the
picture tube, to ensure that you've fully discharged the HV capacitor.

Good Luck!
Bobo

 

[Joerg]

Hello Jim,

Loss of contrast.

That could be a CCFL tube going (or the switcher feeding them).

Bought this set the day of 9/11 so I could keep track of happenings
without leaving my desk... I was in the midst of a big project. So I
doubt if it was built to RoHS.

I just meant the stuff that's coming. With the EU having gone crazy
about RoHS there will be lots of electronics gear shoved onto our market
that is compliant. And that might not be a good thing.

Natch. I probably should just go buy a new set and forget about it.
The replacement AC adapter alone is $126 :-(

I have seen a small LCD 14-inch TV at a big store (Walmart?) for about
$250. It didn't quite have the contrast that our outdoors tube set does.

Unloaded it's bouncing around.

That is not a good sign. Either shot or of poor design.

I'd use a bench supply but, in my world, 4A is unheard of. All I have
is small supplies good to 300mA.

A fully charged car battery might work if the set is happy with about a
volt less. Assuming this is a 15" set I am surprised it needs a 60W supply.

 

[Tim Shoppa]

The TV I bought for my office on 9/11/2001 has gone on the fritz...

Panasonic TC-15LT1

Warms up, then flicks back and forth between a perfectly good picture,
then totally washed out. Sound always stays good.

My two cents: Toss the TV. The world of network TV that you and I grew
up with is gone. The last universally shared experience of US culture
was watching the 9/11 damage over and over again, and we saw enough of
that 5 years ago. What we're left with is a bazillion channels of HDTV
nonsense.

Who's the best source for a schematic? I'm leery of the Russian
sites, which seem to dominate this topic.

Use the space formerly taken up by the TV to buy some ex-soviet
military technology (maybe not the same sites, but maybe adjacent
ones!) to sit in your office. On E-bay there's a lot of interesting
stuff coming out of Ukraine/Georgia/Russia right now.

Tim.

 

[Jim Thompson]

Hello Jim,

[snip]

It has an external 15V/4A "power block". I'm beginning to be
suspicious of that.

Easy. Hook a digital scope to it and let it log the 15V in slow motion.
Or use a bench supply and see if the TV repeats the error.

Unloaded it's bouncing around.

That is not a good sign. Either shot or of poor design.

I'd use a bench supply but, in my world, 4A is unheard of. All I have
is small supplies good to 300mA.

A fully charged car battery might work if the set is happy with about a
volt less. Assuming this is a 15" set I am surprised it needs a 60W supply.

It's 16" letter-box.

...Jim Thompson

 

[Jim Thompson]

My two cents: Toss the TV. The world of network TV that you and I grew
up with is gone. The last universally shared experience of US culture
was watching the 9/11 damage over and over again, and we saw enough of
that 5 years ago. What we're left with is a bazillion channels of HDTV
nonsense.

[snip]

What? And not be able to watch Fox News ?

...Jim Thompson

 

[Joerg]

Hello Jim,

It's 16" letter-box.

Wow, wonder why it needs so much more juice than a CRT set.

Regarding power, check this out:

http://www.caiso.com/outlook/SystemStatus.html

It's our CA power grid supply-demand situation on a scorcher day (by
non-Arizonian standars). Under our previous governor the green supply
side line would often have continued flat at 11:00am and it seems we
would have lost electricity by 12:30pm.

 

[Joerg]

Hello Jim,

What? And not be able to watch Fox News ?

There is always Rush...

 

[Tim Shoppa]

What? And not be able to watch Fox News ?

Is that the channel that the Huntley-Brinkley report is on now?

Tim.

 

[martin griffith]

My two cents: Toss the TV. The world of network TV that you and I grew
up with is gone. The last universally shared experience of US culture
was watching the 9/11 damage over and over again, and we saw enough of
that 5 years ago. What we're left with is a bazillion channels of HDTV
nonsense.

[snip]

What? And not be able to watch Fox News ?

...Jim Thompson

I dont have a TV, almost 4 years now, but I see the UK is going even
more down market with imported US crap
http://www.theregister.co.uk/2006/07/18/tv_spectacular/

OK well, it is Arnulds pitch


martin

 

[Jim Thompson]

Is that the channel that the Huntley-Brinkley report is on now?

Tim.

I'm old enough to remember Chet and Dave as *the* standard for news
casting.

...Jim Thompson

 

[Martine Riddle]

The TV I bought for my office on 9/11/2001 has gone on the fritz...

Panasonic TC-15LT1

Warms up, then flicks back and forth between a perfectly good picture,
then totally washed out. Sound always stays good.

Who's the best source for a schematic? I'm leery of the Russian
sites, which seem to dominate this topic.

I allways ran over to the local library. There is one not too far that had a
pretty complete Sams on hand. A couple of dimes in the machine and I was
off.

Cheers

 

[Martine Riddle]

Hello Jim,


Wow, wonder why it needs so much more juice than a CRT set.

Regarding power, check this out:

http://www.caiso.com/outlook/SystemStatus.html

Looks like the Conserv-o-meter is saying something. Maybe its time to turn
off the Christmas Lights?


Cheers

 

[Rich Grise]

I'm old enough to remember Chet and Dave as *the* standard for news
casting.

I remmber when they won some award, and Carol Burnett was hosting
that particular presentation, only weeks after they'd had a "Huntley-
Brinkley" parody on the Carol Burnett show, and when she opened the
envelope, she grinned from ear to ear, as only she can do, and proudly
announced, "Buntley-Hinkley".

Cheers!
Rich