bad tv screen help - screen condensed into 1 inch line --Solved--

[cptnwhlz]

Pretty much all i have for you is that every once in awhile the screen shrinks into a bright, one inch or so line.  I can tell its the image just shrunk alot, as i can see the "VIDEO" all squished in the top corner and i can kinda make out the image.  Usually a lite tap helps but it will go back from a couple of minutes to a half hour later. 

Any help would be great.  Since hitting it helps im guessing something loose?  Im not too scared to pop it open, ive worked with a tv before, but I am not exactly great with them. 

[Kevin Mullins]

First off, don't run it much more like that, liable to just make things worse.

Open it up and pull the chassis out enough to see the underside, solder joints etc.
I'm betting you have a bad solder joint that just needs touched up.
Check around where the yoke plugs into the chassis. (check the rest of the chassis too while you're at it though)

[qrz]

loose connection in vert deflection .

most likely on the output ic.    the chip will be on a heatsink .

 look for a ta, la, an prefix on the chip

some examples are
an5521
la7836
ta1771

qrz

[cptnwhlz]

I gave it a go just now and pulled out the board to look for that chip.  It took awhile but i found one with an "an" prefix, but the joints looked great, and they were really smalls pins and my soldering iron has a relativly big tip, so i didnt want to try touching those up.  I looked at the yoke and everything looked great there and touched up what didnt look 100% perfect.  I tightened up every cable connection and put it all back in.

It worked for about 15 minutes after plugging it in and went back to bad.  It was a little bit "better", as it gave an image of about 6 inches, but the image was all over the place if that makes much sense. 

Any other ideas? Am i totally missing something you told me?  Thanks for all the help so far, btw.

[qrz]

well, it would help us to help you if the model number was posted 

you do have a vertical deflection issue caused by a loose connection.

descrete output stages use 3 or more xistors. whereas an integrated output uses an IC.
due to the generated heat , the solder on heatsinked devices tend to degrade, resulting in intermittent connections.
vert ICs are usually in a 7 or more pin single inline package ( SIP )

also note that the IC versions operate as a closed loop. so be aware that a loose connection anywhere , including the feedback loop/vhold/vsize / can cause vertical instabilities

qrz

[cptnwhlz]

I tried taking a couple of pics of what I had here.  I tried taking  a close up of the chip itself, but my camera is not that great.  The chip says: "an5849s"  and it wasnt anywhere near a heatsink of any sort.   Here is a couple of pics if it can help anyone lead me to what may need to be touched up.

Sorry about how blurry that last pic is.  I couldnt get a good close up shot of the chip, but I figured I would post what I got.

[qrz]

the vert out IC is an la7845 (IC451).  located on the heatsink to the left and down from the tuner in pic 2
 resoldering the ic should cure it....

i have a Sam's Photofact (#4435) in pdf on this .  2.3mb
pm an addy - if u want it


qrz

[cptnwhlz]

I can barely believe it, but it worked!  I was a little scared to take a soldering iron to it, but it went smoothly!  Never would have gotten then done without your help =)


thanks!

[qrz]

like any new skill , with more practice - the better one becomes ....

glad u got it   


qrz