12 Dec
2000
12 Dec
'00
12:35 a.m.
I discharged my TV based on information I found on archives of this
mailing list and some over-the-phone advice from a friend. The only
difference was that I used a high-voltage probe instead of a resistor
(attached the ground to the ground braid and dsicharged from the metal
behind the suction cup).
I then did some looking around in the dark and my heater seems to be
malfunctioning... it doens't glow, it more sparks. The picture is really
light and fades away to black. It will occasionally come back but
usually fades again right away. So I looked along the little clear bulb
on the back of the crt and ther was a small block dot on one part that
looks like somethign underneith it had burned. The dot was about a cm in
diameter.. maybe 2, but it was very small. Does this mean the heater is
blown? If not is it a part I can buy and replace easily?
Thanks.
Phil
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12 Dec
12 Dec
12:48 p.m.
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3:02 p.m.
FWIW, I normally use an HV probe to discharge a CRT as
well. It's a
resistorr that I know will withstand the EHT, and by watching the meter I
can tell when the CRT is discharged.
I lack a meter that works with my probe, but I held it on there for a good
10-15 seconds...
If the heater is going on and off (and if the picture
is OK when the
heater is on), look for bad connections in the heater circuit first.
That's exactly what it's doing.
Often the heater (in a TV) runs off a winding on the
flyback transformer
(the HV transformer that links to the rubber 'flower' on the CRT flare).
Check for dry joints at the flyback transformer pins, dry joints on the
CRT socket, dirty CRT pins, etc.
I don't know which pins that the instructions (or you) are talking about. I
checked all the wire connections... don't know about the joints... (sorry, I'm
new to repairing CRTs.
This sounds like the 'getter'. It's a film
of a reactive metal (barium, I
think) that is evapourated onto the glass when the CRT is finally
evacuated. Any residual oxygen in the CRT will react with the getter
rather than damaging other parts of the CRT.
Umm. I think you may have misunderstood me. The litlte burn mark isnt' on the
CRT, it's on the (I think) heater -- the little clear glass tube on the back
fo the crt that glows when the TV is on... or well is supposed to glow, but
more comes on and off.
But if you get a picture at all, the CRT is still
holding a vacuum. And
the heater is probably OK (they _can_ go intermittant, but it's rare)
Picture comes in and fades to black, comes in and fades to black
Phil
--
Insanity Palace of Metallica
www.ipom.com
webmaster(a)ipom.com
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3:40 p.m.
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11:01 p.m.
I then did
some looking around in the dark and my heater seems to be
malfunctioning... it doens't glow, it more sparks. The picture is really
> light and fades away to black. It will occasionally come back but
> usually fades again right away.
Fading is compatible with the idea that the heater is cooling off, due to an
intermittent.
So I looked along the little clear bulb
> on the back of the crt and ther was a small block dot on one part that
> looks like somethign underneith it had burned. The dot was about a cm in
>
> diameter.. maybe 2, but it was very small. Does this mean the heater is
A 2 cm burn sounds big. I would investigate the cause of the burn. A
intermittent connection can get hot.
-- John Tinker
13 Dec
13 Dec
12:30 a.m.
New subject: CRT Problems was:(no subject)
If the 'burn mark' on the inside of the neck of the tube is silvery-edged
and/or mettallic looking, then it is possible that is the residue of the
"getter" flash. To sweep out the last of the reactive gas molecules that
are left in a vacuum tube (mostly dissolved in the surfaces of the
elements) a small amount of a compound called a getter is caused to burn
inside the tube after evacuation. This absorbs the last bits of gas in the
device and deposits them on the side of the neck.
Note that if this 'getter spot' is grey or has flakey edges (not
silvery) then your CRT is most likely gassy and needs to be sent to
Picture Tube Heaven.
On the other front, if the heater is 'arcing' in the tube, this could
mean that it is actually open and not making contact all the time, or that
there is a short between the heater element and the cathode
structure... both of which scenarios bode ill for your Tube. The picture
disturbances that you report sound like loss-of-emission symptoms that I
would expect to see if the heater/filament is intermittent.
One last Thought: there used to be a quite common little gizmo called a
CRT Rejuvenator... basically it hit the heater/cathode parts with a
momentary elevated voltage to burn away shorts and attempt to re-weld open
heater filaments. You might try this, but it's a Last Resort type of
thing and seldom (if ever) permanent.
Cheerz
John
1:03 a.m.
New subject: CRT Problems was:(no subject)
Thanks to all who have responded... based on many replies, I think I
understand everything well enough to ask better questions:
If the 'burn mark' on the inside of the neck
of the tube is silvery-edged
and/or mettallic looking, then it is possible that is the residue of the
"getter" flash. To sweep out the last of the reactive gas molecules that
Yeah, silvery, not flaky. So that's a good thing
On the other front, if the heater is
'arcing' in the tube, this could
mean that it is actually open and not making contact all the time, or that
there is a short between the heater element and the cathode
structure... both of which scenarios bode ill for your Tube. The picture
disturbances that you report sound like loss-of-emission symptoms that I
would expect to see if the heater/filament is intermittent.
Ok, what exactly does it mean for a heater to be arcing? It starts to glow
then stops, then starts, then stops.
Also, Several people have have used intermittent in this context and I'm not
quite sure I understand... it is intermittent in the fact that it
intermittently starts and stops glowing...
I have my TV closed again, but when I open it up again I want to have a list
of all the things I need to look for and what to do about them. So far, I know
I need to look for bad connectiions, broken 'pins', to make double sure the
little mark is silvery instead of gray. However, all the wires and soldering
seemed to be in tact, of the connections I could see everything was fine. BTW,
I'm relatively (70%) sure I know what parts are what based on descriptions
here, but does anyone know of a site with pictures that labels different parts
so I can get a better idea of what is what? Thanks.
Phil
--
Insanity Palace of Metallica
www.ipom.com
webmaster(a)ipom.com
--
10:08 a.m.
New subject: Fixing CRT heaters (was: Re: CRT Problems)
Hi,
On Wednesday 13 December 2000 01:03, you wrote:
understand everything well enough to ask better
questions:
Great, then it's not a burn, it's a good sign. If the silvery deposit becomes
hazy or translucent, it means that the tube is losing vacuum. Tubes with weak
vacuum run hot, which compounds the loss of life.
However, your problem with the intermittent heater is a pretty common thing
to have happend in the old days. There is a way to fix it, usually... You
will need to find someone with a picture tube tester that has the filament
'repair' feature. What this really is, is a fairly large (500uf or better)
capacitor, that gets charged up to about 250VDC and then is applied across
the (open) heater contacts on the tube. It helps to first jar the tube
slightly, and test to make sure that the heater is (at least at that moment)
totally open, before applying the voltage.
Now the voltage is applied. The tube is then jarred slightly, until the open
heater makes a light contact, at which time the cap discharges like a mini
arc-welder and tags the heater filament back in place. This works well, and
can be done many times. If your heater is open internally, this is the best
(and only) route for effecting a repair.
Good luck, I hope you are able to fix it.
--
Bill Layer
Sales Technician
<b.layer(a)vikingelectronics.com>
If the 'burn mark' on the inside of the
neck of the tube is
silvery-edged and/or mettallic looking, then it is possible that is the
residue of the "getter" flash. To sweep out the last of the reactive
gas molecules that
Yeah, silvery, not flaky. So that's a good thing 
11:36 a.m.
New subject: CRT Problems was:(no subject)
-> Also, Several people have used intermittent in this context and I'm
not
-> quite sure I understand... it is intermittent in the fact that it
-> intermittently starts and stops glowing...
Yes.
-> I have my TV closed again, but when I open it up again I want to have
a list
-> of all the things I need to look for and what to do about them. So
far, I know
-> I need to look for bad connections, broken 'pins', to make double
sure the
-> little mark is silvery instead of gray. However, all the wires and
soldering
-> seemed to be in tact, of the connections I could see everything was
fine.
The thing to look for as far as bad connections go is a cold solder
joint. These are a result of thermal fatigue/cycling and physical
stresses. You should look _very_ closely in the places Tony mentioned,
especially where the CRT socket is soldered to the little board at the
rear of the CRT and where the flyback is soldered to the mainboard. A
cold solder joint will usually look normal without a close inspection
(unless you have a lot of experience at these things), but a closer look
will reveal a slight ring around the socket pin, flyback pin or wire,
within the circumference of the solder pad. Sometimes the contact will
be bad right at the solder/pin interface. That is unless the solder has
totally popped away from the circuit pad, which is another type of cold
solder joint related to initial improper soldering. I'd recommend
resoldering every connection for the CRT socket and flyback transformer
and seeing if this fixes the problem.
If you are inexperienced at soldering/resoldering, I'm sure we can
start a new thread. d8^)
Bill
8800
days inactive
8801
days old
8 comments
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participants (6)
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ard＠p850ug1.demon.co.uk -
b.layer＠vikingelectronics.com -
jpl15＠panix.com -
jtinker＠coin.org -
webmaster＠ipom.com -
whdawson＠mlynk.com