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Crumbtrail TV Forums: TV Equipment: TV Repair Forum:
Now No Picture???

 
 


Wiz
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Sep 4, 2005, 10:21 PM

Post #1 of 7 (2041 views)
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Now No Picture??? Can't Post
Hey,

I have a 28" Naiko TV (N2850W) that had problems with horizontal deflection (vertical line down center of screen) There were a few dry joints in it and these were soldered up, which made the picture wider, however it didnt cover the screen (4:3 size rather than 16:9) and had a pincusion effect. Eg. ) (

I thought that this may just be something in the menu that needed to be adjusted, however, after a few minutes the picture got narrower, and eventually back to the vertical line. I switched the TV off, and when turned back on again, the pincusion effect as before was present.

Do I need to look for more dry joints, or is there any components, caps etc. that could be causing this fault, or could this be something more serious?

Any help apprieciated,

Oliver


(This post was edited by TheOW on Sep 6, 2005, 3:45 PM)



Wiz
User


Sep 5, 2005, 10:21 AM

Post #2 of 7 (2032 views)
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Re: [oliverwestby] Picture gets narrower ??? [In reply to] Can't Post
Update, I connected all the wires back up after carefully resoldering the dry joints, however now when i turn the tv on, I get a flicker of light at the sides of the screen, and then a weird noise for a few seconds that descreases in pitch. Then the TV stays on for a couple of seconds with no picture and no noise, before switching onto standby.

Can anyone help.

Oliver


rrobor
Veteran

Sep 5, 2005, 11:35 AM

Post #3 of 7 (2030 views)
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Re: [oliverwestby] Picture gets narrower ??? [In reply to] Can't Post
Simple answer is no, We dont know what you have done, It was a dry joint on the yoke socket or S shaping capacitor, now you have created a short and probably blown the output transistor. Get help on this as it seems you are just adding to the bill.


Wiz
User


Sep 5, 2005, 9:11 PM

Post #4 of 7 (2023 views)
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Re: [rrobor] Picture gets narrower ??? [In reply to] Can't Post
A friend of mine (DKendall) got me into TVs, so to practice/have fun, I have got a few TVs from the local dump for a couple of quid so not really minding if I kill it any further. I have gone round the places that I resoldered, checking for any shorted bits, and found none. I think that the output transistor is ok. (reads similar ohms to another one that I have.)

Could there be any other components that could be dead that may be causing this?

Oliver


(This post was edited by oliverwestby on Sep 5, 2005, 9:13 PM)


Wiz
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Sep 5, 2005, 10:35 PM

Post #5 of 7 (2017 views)
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Re: [oliverwestby] Picture gets narrower ??? [In reply to] Can't Post
I take back what I said about the output transistor. I have checked and rechecked the board, and now it will turn on, and stay on, however, there is no picture, so im thinking something to do with the LOPT or controlling components.

Another point to note is that when turning on the tv, there is a pop from the speakers, and when turned off there are a few quiet pops from the speakers. I dont know if this has anythng to do with the problem or not?

Oliver


Wiz
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Sep 6, 2005, 10:57 PM

Post #6 of 7 (1995 views)
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Re: [TheOW] Picture gets narrower ??? [In reply to] Can't Post
Argh.

Does the HOT control the catode voltages from the LOPT?
The output to the cathodes is about 320v DC on the cathode pin and 400v DC on pin 4 on the LOPT.
I thought that this was suposed to be about 200v DC.

I touched the cathode pin to heater pin to lower the voltage of that, and got a bright blue screen, making me think that the voltage on the cathodes is too high. could it also be that the anode has too lower voltage? What could be causing this?

Oliver


EDIT: Was measuring incorrectly, these voltages read correctly


(This post was edited by TheOW on Sep 7, 2005, 11:09 PM)


Wiz
User


Sep 7, 2005, 11:08 PM

Post #7 of 7 (1975 views)
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Re: [TheOW] Picture gets narrower ??? [In reply to] Can't Post
Using an Oscilliscope, I have worked out that the R, G and B tracks from the chip TDA9353 have no signal, sugesting to me that this chip has died, or something to do with it has died. Would this also explain the narrower, pincusion effect? or am I dealing with more than one problem here?

Also where can I get a new chip from?

 
 
 


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