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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)

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(closeup of area that may be the problem...)

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(power supply board)

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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

Reply to
rpesq
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In data Sun, 18 Jun 2006 05:41:26 +0200, ha scritto:

You have a vertical problem.

Hantarex ? ;)

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

--
Inty.Evolution
intiglietta@email.it -> per email normali e con immagini Jpeg
Reply to
Inty XP

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.

Reply to
default

In data Sun, 25 Jun 2006 17:24:49 +0200, default ha scritto:

MAYBE a blown fuse resistor?

--
Inty.Evolution
intiglietta@email.it -> per email normali e con immagini Jpeg
Reply to
Inty XP

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 > In data Sun, 25 Jun 2006 17:24:49 +0200, default ha scritto:

Reply to
rpesq

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

Reply to
rpesq

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