It would take a very large lightning hit to magnetize or damage a CRT.
The set would have been destroyed first! I think the screen became
magnetized, and should be able to be demagnetized. But, if he dropped
the set, banged it very hard, or put a very strong magnet to the mask of
the screen, this would do permanent damage to the tube.

After thunder storms sometimes we have seen people try to make
questionable insurance claims for equipment that is defective. This is
something that cannot be indicated openly without proper evidence.
Insurance companies have many claims from people for damages that are
not even relative to the event.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
==============================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
Instruments http://www.zoom-one.com/glgtech.htm
==============================================
"Bill" wrote in message
om...
Hello folks- I have an RCA TV chassis # CTC185AB. Customer said
after a severe storm he started getting weird colors on the screen.
Picture is perfect. I checked for blown parts and found none. I
resoldered some joints and replaced the deg. thermister just to be
sure. I also tried to clean these patches of color externally via a
deg. coil. I made some progress but the corners are still messed up.
I'm starting to believe he dropped it. Can storms do so much damage
that the screen can't be completely demagnetized ? What other
solutions are there in this case other than placing magnets on the CRT
? Thanks

"Sam Goldwasser" wrote in message
...
"Clifton T. Sharp Jr." writes:

Jerry G. wrote:
It would take a very large lightning hit to magnetize or damage a CRT.
The set would have been destroyed first! I think the screen became
magnetized, and should be able to be demagnetized.

Every time I drive past that house, I remember the first time I ran into
a set magnetized by a close lightning strike. It was extremely weird.
The red purity was fine, so were blue and green. But the color picture
looked like severe purity problems. I called the head tech, who told me
to degauss; I was amazed when it fixed the problem.

Yes, the effects of a close lightning strike and nuclear EMP might be very
similar (at least in terms of magnetization of a CRT!).

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work.
To
contact me, please use the Feedback Form at repairfaq.org. Thanks.

I had a strike around eight years ago which took out many, many electronic
devices in my home. Partial list includes vcr (no audio...video fine),
several telephones, one PC and most everything attached to it (even blew out
one of the tweeters on the speakers attached, along with the parallel port
of the printer), another pc which I was able to partially resurrect (blew
out all onboard external ports and HD interface...replaced with ISA/PCI
cards, worked like that for many years until I finally scrapped it).

It literally blew my neighbors telco interface box off the wall of his
house...blew the bark off a stately old oak tree in my back yard (3" strip
running radially from the ground up to about 20'...mostly healed over now,
but I wonder if it will ultimately kill the tree).

The interesting thing is that other many devices survived, including the fax
machine connected to the same line as one of the dead phones, a couple of
other phones, a couple of other vcr's and all of the TV's/monitors in the
house (including the ones connected to the above pc's).

One common thread, however, was that *every* color crt device connected to
a/c mains at the time--whether switched on or not--had severe purity
problems...most of which worked themselves out over the next several days
with normal on/off switching (before most monitors had on-screen
menus/manual degaussing).

So, for the previous poster (not you Sam), it's *very* possible to induce
enough emf into a crt--by way of a lightning strike--to cause the problem
the OP described...without destroying the device.

The symptoms will likely disappear after a few power on/off cycles. If it's
possible to view as is, just wait a few days. Normal usage will eventually
degauss it. If it's particularly severe, you may have to degauss it
manually (if you have a coil). I wouldn't recommend repeated on/off
switching as a degaussing strategy...could stress other components of the
set.

jak

Jerry G. wrote:
It would take a very large lightning hit to magnetize or damage a CRT.
The set would have been destroyed first! I think the screen became
magnetized, and should be able to be demagnetized.


This summer we had some thunderstorms here, luckily we don't have many.
The TV was on (counting seconds between flashes and thunder were typ.
10-20 seconds)
Suddenly it came closer, I heard a faint 'snap' which came from the area
where the TV and VCR was. The TV had a strange image: Green circle
inside the edges of the screen, 'dirt brown' colours inside this circle....
I immediately switched off and disconnected power and antenna plugs,
thinking 'why didn't I disconnect it at once'..
Later, when the storm passed, I connected the equipment again and
switched on. Luckily, the TV was fine again, the screen had probably
been magnetised as you said, but the power-on degaussing seemed sufficient.
As for the 'snap' I haven't found any visible or measurable faults...


Stein

In article , jakdedert wrote:

"Sam Goldwasser" wrote in message
...
"Clifton T. Sharp Jr." writes:

Jerry G. wrote:
It would take a very large lightning hit to magnetize or damage a CRT.
The set would have been destroyed first! I think the screen became
magnetized, and should be able to be demagnetized.

[....] to degauss; I was amazed when it fixed the problem.

Yes, the effects of a close lightning strike and nuclear EMP might be very
similar (at least in terms of magnetization of a CRT!).

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/

I had a strike around eight years ago which took out many, many electronic
devices in my home. Partial list includes vcr (no audio...video fine),
[....]
It literally blew my neighbors telco interface box off the wall of his
house...blew the bark off a stately old oak tree in my back yard (3" strip
running radially from the ground up to about 20'...mostly healed over now,
but I wonder if it will ultimately kill the tree).

this is the common result of tree strikes, in the Mt's of NM they
call it "cork screwing". the step up from this is when the trunk
actually explodes as the sap is vaporized inside the tree.

--Loren (formerly from Cloudcroft, NM)

Most definitely lightning can do this. This happened to RCA/GE (before
Thomson) at their warehouse in Tampa Florida. A lamp pole in their parking
lot was hit hard by lightning and destroyed the CRTs of almost 1000 sets. It
was the EMF, not the static, that was to blame. The electronics worked but
the CRTs were really messed up. Especially the larger ones.

"Bill" wrote in message
om...
Hello folks- I have an RCA TV chassis # CTC185AB. Customer said
after a severe storm he started getting weird colors on the screen.
Picture is perfect. I checked for blown parts and found none. I
resoldered some joints and replaced the deg. thermister just to be
sure. I also tried to clean these patches of color externally via a
deg. coil. I made some progress but the corners are still messed up.
I'm starting to believe he dropped it. Can storms do so much damage
that the screen can't be completely demagnetized ? What other
solutions are there in this case other than placing magnets on the CRT
? Thanks

I've had this before. It was a Sony and was so evenly magnetized that the
colors were interpolated, but the purity was actually good. The degausssing
coil couldn't handle it, nor could an external one. What I wound up doing was
wiring a variac right to the DG coil and cranking it all the way up and
bringing it down slowly.

I have read warnings about using to strong of a degausser on a Sony, but it
seems that might apply more to the magnets rather than the CRT itself, plus in
this case there was really no other choice but to rotate the color drives. That
would be ridiculous.

Basically the variac trick worked just fine.

JURB