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#161101 - 03/30/07 01:16 AM OT: TV problem
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Guys,
I've got a problem here with a TV set that is killing me.
My Brother in Law (sisters hubby) gave me the TV after I came home from holiday and asked me if I could fix it.
The TV is a Mitsubishi 25" of 1999 build, the Chassis No. I've still yet to get as I haven't really spent a lot of time on it to be honest.
The complaint was that after running for roughly 30 minutes the screen would reduce to a 1" line and then a dot.
I was thinking a dry joint, somewhere on the Main board, I've looked at the Main board about twice and can't see anything wrong with it.
Frustrated, I started poking around with an oscilloscope, but everything seems to be where it should be.
There are no sounds of arcing and I have frozen most parts of the boards in the set with (dare I say it) old Freon spray.
The real nuisance about this is the fact that you can't get service manuals or any real info about gear like this without paying for it, this TV set is long obselete, but try and find any useful information on it.
I'm not doing this repair for money, just for the hell of it and my BIL knows it.
I just want to save another TV from a premature trip to the dump.
Anyone got any ideas?.


{Edit: Please don't think that this is an area where everyone can send their "My Appliance is broken can you help me fix it" type threads, I've repaired TV's and associated things for 20 years. }


Edited by Trumpy (03/30/07 01:19 AM)
Edit Reason: To add last bit
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#161108 - 03/30/07 04:23 AM Re: OT: TV problem [Re: Trumpy]
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
 Quote:
The complaint was that after running for roughly 30 minutes the screen would reduce to a 1" line and then a dot.


Do you mean 1" high, or 1" wide? If the former, then clearly a problem in the vertical scan section; if the latter the line scanning, although in any modern set that would have an effect on the EHT as well.

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#161150 - 03/30/07 05:07 PM Re: OT: TV problem [Re: pauluk]
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
I had a somewhat similar problem with an older model Mitsubishi CRT Television Receiver - seems like it was also 25" Screen - but was circa 1994-ish.

The problem encountered was Vertical Rolling after about 30 Minutes.

Turned out to be a poor design issue / heat related issue.

There was a Ceramic Power Resistor, which ran red hot during normal usage, and it would dissipate heat into a nearby PCB via the metallic shielding nearby (through heat sinking).
That PCB contained the ICs for Vertical + Horizontal control.

The fix I employed was installing a "Muffin Fan" in the case, and controlling it through a Relay. The Relay coil was connected to the "Load" side of the main power control (master "On/Off").

Fixed the problem, but generated a lot of sound (the Fan was loud!).

Maybe your experiencing similar issues on your Receiver.


Edited by Scott35 (03/30/07 05:08 PM)
Edit Reason: Brain In Idle!
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Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#161172 - 03/30/07 10:45 PM Re: OT: TV problem [Re: Scott35]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
You are probably going to have trouble finding parts. If it isn't the horizontal output transistor or a Radio Shack componant like a resistor you are going to have a problem. These TVs are assembled in Asia somewhere and they usually do not have a real "replacement part" infrastructure since TVs don't break that often and people just toss them.
I suppose Sams may still sell you a book.
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#161189 - 03/31/07 07:49 AM Re: OT: TV problem [Re: gfretwell]
geoff in UK Offline
Member

Registered: 12/30/02
Posts: 172
Loc: UK

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#161191 - 03/31/07 08:02 AM Re: OT: TV problem [Re: geoff in UK]
geoff in UK Offline
Member

Registered: 12/30/02
Posts: 172
Loc: UK

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#161202 - 03/31/07 09:04 AM Re: OT: TV problem [Re: geoff in UK]
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
 Quote:
If it isn't the horizontal output transistor or a Radio Shack componant like a resistor you are going to have a problem


Yep, getting model-specific components has become darned-near impossible. Long gone are the days when you could buy a replacement LOPT at a reasonable price, or even things like replacement scanning coils. You'll be lucky to source them at all, nevermind at a sensible price. \:\(

About the only way to find some of these parts is to canibalize another set.

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#161232 - 03/31/07 04:05 PM Re: OT: TV problem [Re: pauluk]
classicsat Offline
Member

Registered: 11/23/02
Posts: 449
It could be a wonky capacitor.

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#161601 - 04/05/07 02:25 AM Re: OT: TV problem [Re: classicsat]
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
It has been fixed,
I shoved some cooling spray in the direction of the LOPT and the problem went away.
Next thing was to find a replacement.
I have a few TV sets here laid to waste, but none had the same specs as far as the LOPT went.
I rang a mate of mine that has a whole (spare) bedroom full of TV sets and he desoldered just the right one.
Job done, my sister and BIL will be happy once they come back from the US on thier holiday.
BTW, sorry to go off topic (un-usual for a thread that I'm involved with), anyone know of a good steak-house in Boston?.
That was in an e-mail from my sister.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#161644 - 04/05/07 06:48 PM Re: OT: TV problem [Re: Trumpy]
RODALCO Offline
Member

Registered: 12/08/05
Posts: 863
Loc: Titirangi, Akld, New Zealand
I built in two 115 Volts fans in series in my old 25 YO Philps TV, which finally died but did not need any maintenace for the last 15.
Haven't had the time to find the fault yet.
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The product of rotation, excitation and flux produces electricty.

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