Help fixing Mitsubishi TV model CK35304

Hi guys,
Need help to repair Mitsubishi console TV model CK35304. (36-inch,
manuf. date 1994).

Approx a month ago, when you would turn on the TV each day for the
first time, the top of the screen would be shrunk down a few inches.
As TV warmed up, the screen would return to normal. Color and clarity
of picture has been excellent throughout.

The other day, turned it on, just get a line thru the middle of the
tube. So, whatever was going bad, has definitely gone bad. I do not
have TV repair experience, but I have experience repairing other
high-voltage items, such as many Tube Guitar Amps, antique radios,
PC's, and even rebuilt a Video Game monitor once (installed a capacitor
kit). So I am familiar with the voltages involved.

I talked with a friend of mine who repairs TV (lives several hours away
from me...), and while he is hesitate to tell me a lot (he never tells
the secrets of the trade, so to speak...), he said that this a typical
problem with Mitsubishi TVs, and that the problem is probably in the
Vertical output circuit, then said 'maybe 5 capacitors, probably a
chip, and maybe a fuse'.

Here are some photos of the boards inside the set:

(mainboard)
http://mysite.verizon.net/cowman136/tv1.jpg

(closeup of area that may be the problem...)
http://mysite.verizon.net/cowman136/tv2.jpg

(power supply board)
http://mysite.verizon.net/cowman136/tv3.jpg

You guys can tell me whether my friends general advice is accurate or
not. For starters, I have proceeded assuming his advice was good, and
did some searches to try to narrow down what I am looking for.

Doing some Google searches based upon part numbers on the transistors
that I see on the mainboard (picture "tv2.jpg" above) , I found that
TA8427K is apparently my Vertical Deflector chip, that C2073 is
apparently my Vertical Output chip. In this circuit, I see the
following components (and checked them in-circuit, where noted:
- fuse (checks good)
- 15K ohm 3 watt resis. - checks good, approx 14K ohms in circuit
- 4700uF at 10V cap - did not test
- 2.7 ohm resistor - good
- 2700 ohm resis - good
- red capacitor approx 1 inch size with numbers (2A : 335K S) - value
unknown, not tested
- resistor with bands of "yellow - purple - gold - gold" - tests approx
4 ohms.

My photo tv1.jpg above highlights this area of the board. I do not see
any visibly burned components or exploded/leaking caps.

Assistance is MUCH appreciated. I really need to fix this myself, as
cash is very tight. I do not mind installing a few "extra" parts,
shotgun approach is fine. Also, advice as to where is best to buy the
parts (the IC's, as I probably have the caps & resistors) will be
appreciated. THANKS.
BJ

In data Sun, 18 Jun 2006 05:41:26 +0200, <(E-Mail Removed)> ha scritto:

> Approx a month ago, when you would turn on the TV each day for the
> first time, the top of the screen would be shrunk down a few inches.
> As TV warmed up, the screen would return to normal. Color and clarity
> of picture has been excellent throughout.

You have a vertical problem.

> The other day, turned it on, just get a line thru the middle of the
> tube. So, whatever was going bad, has definitely gone bad. I do not
> have TV repair experience, but I have experience repairing other
> high-voltage items, such as many Tube Guitar Amps, antique radios,
> PC's, and even rebuilt a Video Game monitor once (installed a capacitor
> kit). So I am familiar with the voltages involved.

Hantarex ?
>
> I talked with a friend of mine who repairs TV (lives several hours away
> from me...), and while he is hesitate to tell me a lot (he never tells
> the secrets of the trade, so to speak...), he said that this a typical
> problem with Mitsubishi TVs, and that the problem is probably in the
> Vertical output circuit, then said 'maybe 5 capacitors, probably a
> chip, and maybe a fuse'.
>
> Here are some photos of the boards inside the set:
>
> (mainboard)
> http://mysite.verizon.net/cowman136/tv1.jpg
>
> (closeup of area that may be the problem...)
> http://mysite.verizon.net/cowman136/tv2.jpg
>
> (power supply board)
> http://mysite.verizon.net/cowman136/tv3.jpg
>
> You guys can tell me whether my friends general advice is accurate or
> not. For starters, I have proceeded assuming his advice was good, and
> did some searches to try to narrow down what I am looking for.
>
> Doing some Google searches based upon part numbers on the transistors
> that I see on the mainboard (picture "tv2.jpg" above) , I found that
> TA8427K is apparently my Vertical Deflector chip, that C2073 is
> apparently my Vertical Output chip. In this circuit, I see the
> following components (and checked them in-circuit, where noted:
> - fuse (checks good)
> - 15K ohm 3 watt resis. - checks good, approx 14K ohms in circuit
> - 4700uF at 10V cap - did not test
> - 2.7 ohm resistor - good
> - 2700 ohm resis - good
> - red capacitor approx 1 inch size with numbers (2A : 335K S) - value
> unknown, not tested
> - resistor with bands of "yellow - purple - gold - gold" - tests approx
> 4 ohms.

This resistor was good ! (yellow-purple-gold = 4,7 ohm)

Changing components without measures isn't a good idea.
Start from changing all electrolytic caps in that zone, then

>
> My photo tv1.jpg above highlights this area of the board. I do not see
> any visibly burned components or exploded/leaking caps.
>
> Assistance is MUCH appreciated. I really need to fix this myself, as
> cash is very tight. I do not mind installing a few "extra" parts,
> shotgun approach is fine. Also, advice as to where is best to buy the
> parts (the IC's, as I probably have the caps & resistors) will be
> appreciated. THANKS.
> BJ
>



--
Inty.Evolution
(E-Mail Removed) -> per email normali e con immagini Jpeg

> (closeup of area that may be the problem...)
> http://mysite.verizon.net/cowman136/tv2.jpg


This is the flyback transformer area. If the design has the vertical
circuits power supplied by the flyback, then your height shrinkage could be
a premature sign the flyback is breaking down, or there could be a problem
only in the vertical circuit....changing all capacitors in the vertical
circuit is a common solution to certical problems, however the flyback xfmr
in that chassis is common fail\, so its of not it be mentioned.

In data Sun, 25 Jun 2006 17:24:49 +0200, default <(E-Mail Removed)> ha scritto:

>
>> (closeup of area that may be the problem...)
>> http://mysite.verizon.net/cowman136/tv2.jpg
>
>
> This is the flyback transformer area. If the design has the vertical
> circuits power supplied by the flyback, then your height shrinkage could
> be
> a premature sign the flyback is breaking down, or there could be a
> problem
> only in the vertical circuit....changing all capacitors in the vertical
> circuit is a common solution to certical problems, however the flyback
> xfmr
> in that chassis is common fail\, so its of not it be mentioned.


MAYBE a blown fuse resistor?
>
>



--
Inty.Evolution
(E-Mail Removed) -> per email normali e con immagini Jpeg

Hi,

Thanks to `Inty` and `default` for replies.

The fuses all check fine, unless I am not seeing all of them. I am
familiar with fuse-resistors, too.

Update: I changed the 3 electrolytics in the vertical circuits (100mfd
at approx 35V), and they did not help. I checked the caps that I
removed, and all were close to 100mfd (the weakest tested 88 mfd).

Talked to 2 guys (my original source, and another guy that I know who
was in the tv sales/service business for many years), and both guys
believe that 99% likelihood that the problem is defective TA8427K
vertical deflector chip. Both guys said this part goes bad regularly.
So I have already unsoldered it, and have ordered a replacement. Cheap
solution if it works. Less than $8 including postage for a real
Toshiba chip. Should arrive in a few days. If that does not fix it,
we'll go from there.

The only thing that I wonder about, is that my friend asked me to check
whether there is 24V from pin 6 to ground on TA8427K. Well, I got 0,
although it was `damn hard` to get a reading in that area of the board
while the set was operating. It is possible I was not getting good
contact with my meter. Assuming the 0 is accurate, he says that means
something else is wrong, although he feels that the chip is probably
bad also (which he originally said I should replace). So I Look around
on the board, there is not many components in that area. A diode goes
directly to pin 6 of TA8427K, and a bunch of other diodes are in the
immediate area (all diodes checked normal once I removed the TA8427K),
and of course the 100mfd caps (replaced), and a couple mica caps (very
unlikely to be defective). There is 1 glass fuse in the area, which is
good. He asked me to look for small black square boxes, which he says
would be fuses. There is none of them. I can easily identify the
components in the area, so I really cannot see any way that I am
missing a fuse anywhere. This might be a lot easier with a schematic,
but I doubt at this point it would tell me a whole lot.

I'll know more once the vertical deflector chip has been replaced.
Thanks again.

Inty XP wrote:
> In data Sun, 25 Jun 2006 17:24:49 +0200, default <(E-Mail Removed)> ha scritto:
>
> >
> >> (closeup of area that may be the problem...)
> >> http://mysite.verizon.net/cowman136/tv2.jpg
> >
> >
> > This is the flyback transformer area. If the design has the vertical
> > circuits power supplied by the flyback, then your height shrinkage could
> > be
> > a premature sign the flyback is breaking down, or there could be a
> > problem
> > only in the vertical circuit....changing all capacitors in the vertical
> > circuit is a common solution to certical problems, however the flyback
> > xfmr
> > in that chassis is common fail\, so its of not it be mentioned.
>
>
> MAYBE a blown fuse resistor?
> >
> >
>
>
>
> --
> Inty.Evolution
> (E-Mail Removed) -> per email normali e con immagini Jpeg

SOLVED by replacing the TA8427K vertical deflector chip. Good as new.
Thanks to everyone for their suggestions.