Why does my TV go entirely green?
Bill Frandsen
I picked up a 15 year old TV last summer at a rummage sale for free, and it
had about 1/2 an inch of dust over every single component in the case. After
a couple hours of cleaning/bathing the board with component cleaner, I put it
back together, and it worked fine. Then, over the winter, after it had been
on about 45-60 minutes, it would occassionally flash a full-green screen,
then back to a normal picture. Now, just recently, it has started to do this
after only 15 minutes of use, and then it stays green, and the power must be
shut off for a bit to make it go away for a bit longer. Actual use of the TV
was no more than 2 hours a week (for video-gaming)
When the screen goes green, you can almost make out the image underneath it,
but since it has such an intense brightness, it's nearly impossible. It also
has a fine line that superimposes it tracing left to right horizontally, then
back left diagonally (dropping about an inch) and back right for about 10
times from top to bottom (horizontal scan?)
What could be wrong with the unit? Since I got it free, I could just throw
it away, but if it's something easy (and safe) to fix, then I'd appreciate
any suggestions as to what to replace. Obiously it has something to do with
heat, but beyond that I do not know that much about TV components (other than
which areas to avoid while working on cleaning/tuning them up).
BTW-It's a 19" Sears model (Samsung? tube) with a touch "grounding"
12-channel selector, mfg 1980.
Thanks much.
mark wolfe
On Sun, 19 May 1996 22:12:39 GMT, bfra...@rrnet.com (Bill Frandsen)
wrote:
Check the CRT board, you've got the green gun turning on and staying
on. The diagonal lines are retrace lines, and since the green gun is
saturated, you'll see them during the blanking period. You've
probably got a bad transistor turning the green gun on.
Cul,
Mark Wolfe
Sam Goldwasser
> I picked up a 15 year old TV last summer at a rummage sale for free, and it
> had about 1/2 an inch of dust over every single component in the case. After
> a couple hours of cleaning/bathing the board with component cleaner, I put it
> back together, and it worked fine. Then, over the winter, after it had been
> on about 45-60 minutes, it would occassionally flash a full-green screen,
> then back to a normal picture. Now, just recently, it has started to do this
> after only 15 minutes of use, and then it stays green, and the power must be
> shut off for a bit to make it go away for a bit longer. Actual use of the TV
> was no more than 2 hours a week (for video-gaming)
> When the screen goes green, you can almost make out the image underneath it,
> but since it has such an intense brightness, it's nearly impossible. It also
> has a fine line that superimposes it tracing left to right horizontally, then
> back left diagonally (dropping about an inch) and back right for about 10
> times from top to bottom (horizontal scan?)
> What could be wrong with the unit? Since I got it free, I could just throw
> it away, but if it's something easy (and safe) to fix, then I'd appreciate
> any suggestions as to what to replace. Obiously it has something to do with
> heat, but beyond that I do not know that much about TV components (other than
> which areas to avoid while working on cleaning/tuning them up).
> BTW-It's a 19" Sears model (Samsung? tube) with a touch "grounding"
> 12-channel selector, mfg 1980.
> Thanks much.
Depending on how much you can do yourself, this may be repairable.
However:
If you do go inside, beware: line voltage (on large caps) and high voltage
(on CRT) for long after the plug is pulled. There is the added danger of
CRT implosion for carelessly dropped tools and often sharp sheetmetal
shields which can injure if you should have a reflex reaction upon touching
something you should not touch. In inside of a TV or monitor is no place
for the careless or naive.
--- sam
Red, green, or blue full on - fog over picture:
----------------------------------------------
This could be a heater-cathode (H-K) short in the CRT or a failure
of a component in the chroma circuits or video output (driver board).
Don't panic - heater-cathode shorts in CRTs can often be worked around.
Some simple tests can confirm or rule out other possibilities.
Compare the voltages for the video drive signals to the CRT on the little
board on the neck of the CRT with the CRT both connected and unplugged.
A schematic will help greatly in locating these signals.
If there is a significant difference especially on the bad color, then the
CRT is a likely candidate. Try tapping the neck of the CRT GENTLY (with
it plugged in and while viewing a picture) to see if it is an intermittent
problem.
If there is no significant difference, you may have a bad driver or a problem
in the chroma circuits.
Look for bad connection/cold solder joints, probably on the little
board on the neck of the CRT. Use an insulated stick to gently prod
the board and its components in an effort to induce/cure the problem.
Look carefully for hairline cracks around the component leads.
You can swap components between two colors and/or test with an ohmmeter
on that driver board to determine what is bad. The nice thing about
color monitors and TVs is that there three copies of each of these
components. Swapping and/or comparisons between these is an excellent
diagnostic technique.
Alternatively, interchange the outputs of the bad color with a good one
by jumpering on the video driver board (on the CRT neck). If the bad
color changes, then the problem is in the circuitry and not the CRT.
For more info, see the FAQ at:
New, expanded, updated, and improved general repair notes
for a variety of electronic equipment are available at:
http://www.paranoia.com/~filipg/HTML/REPAIR/
along with a whole lot of other interesting stuff maintained
courtesy of Filip (I'll buy a vowel) Gieszczykiewicz.
I also have an ASCII version of the entire set of articles for
which I am the author. These are available via email (zipped,
uuencoded). The total size is about 1.6 MB uncompressed.
--- sam (s...@stdavids.picker.com)
Mr. Paul
In article <4no6de$7...@news.rrnet.com>,
bfra...@rrnet.com (Bill Frandsen) wrote:
>When the screen goes green, you can almost make out the image underneath it,
>but since it has such an intense brightness, it's nearly impossible. It also
>has a fine line that superimposes it tracing left to right horizontally, then
>back left diagonally (dropping about an inch) and back right for about 10
>times from top to bottom (horizontal scan?)
The key is that you can still see video even with the green screen. It's
probably the picture tube with an almost full short.
The lines are horizontal retrace for the green beam which you normally cannot
see (they are blanked normally, this failure is forcing them to be visible in
spite of the blanking).
To be sure:
Power up the set and measure the voltage at the collector of all three
RGB output transistors when the green screen is visible. Note the transistor
that has a substantially lower voltage than the other two.
Turn off TV and pull the picture tube socket (socket may be on a module), force
is not needed if it will not come off easily check for silicone rubber holding
it to the tube or check for some other sort of retaining fastener.
Now place the socket/module in a safe positition, power up the TV and check the
transistors again. If the low one comes up to approx the value of the others
then it's the picture tube if not you have a problem in the RGB drive circuit.
If it's the picture tube you can try and get it rejuvinated, this failure
responds well to a good rejuvination in many cases.