GE 25" Only a 13" now

I have a GE Model #25GT516 with a Chassis # of CTC185AB manufactured april 1997 .The Lower half of picture is fine but the top half is not there , There are lines every .25 " or so in the top half and they do change colors as the picture changes , the audio is fine. It has theis problem immediatly after being turned on .The TV has had problems before and had its power supply replaced by a shop . Its for or Local Vol. Firehouse so I would like to fix it if I can so we dont have to waste money on a new TV. I am familiar with electronics but its been a while since I did anything with a TV, Ie. since tubes.Any help or a sams would be nice.I havent opened it up yet , and yes I know to to discharge high voltage before getting my paws in there , I learned that one a long time ago.Also anyone know where to buy TV schematics and parts online.

Thank You ,
Lee

 

LeeMe, Is the upper half of the screen thats reduced all black?


Fred

 

Yes sir it is the upper half.Not completely black has lines every quarter of an inch or so . I suspect its the power supply not suppling the verticle.

 

LeeMe, Sound like scan lines at that part of the screen. Flip the chassis and go to the tuner shield (metal box lower right). There are six points on that shield that are soldered to the circuit board, those points are your ground for the upper right area of the board where your EEPROM, and microcomputer are and they tend to crack giving you an open ground. Resolder those points, resolder the pins on U4501(vertical output I.C.), and check to see if capacitors C4505-220uf, C4506-1000uf, C4502-3300uf, and C4501-.22uf are leaky. Also check CR4501-diode #1N4002, there should be at least 24volts at pins #2 and #6 of U4501.



Fred

 

Okay , I got the tv opened up . Low and behold the verticle section there has been pawed with . Some of the components have been replaced .Not the greatest soldering job either.The ids are the not same as the ones you listed.They made a mess on the board and I cant read the id's of some of the stuff thats been replaced.I did replace one of the caps but is was 470 uF, Now there is a distorted view in the top half of the screen.The lines are still there but it tries to display a picture ,it is not of the rright size is comparison with the bottom .The lines are green in color and the center of the screen has a thick line that is white.There is an I.C with the id of u501 mounted on a verticle heat sink.Pin 2 has 24 volts on it but pin 6 only has 8.75 volts.

 

LeeMe, Part of your problem is at pin#6. Check to see if CR4501 is leaky or if C4505 was removed and reinstalled backwards. These are the voltages that should present or close too on pins of U4501.

Pin#1. 9.0vdc
Pin#2. 24vdc
Pin#3. 1.2vdc
Pin#4. Ground
Pin#5. 12.9vdc
Pin#6. 24.3vdc
Pin#7. 8.2vdc

Pins#2and #6 are tied together by CR4501.

If in fact the soldering is that bad check for solder bridges.



Fred

 

I resoldered all the pins and took away the extra solder , when I first turned it on same thing , then it started working.I did some voltage measurements while it was still not working and only had 8 volts on the other side of diode then again when it started working ,it now has 24 and it works I am going to take diode out and replace it .Thank You very much , the guys at station will be happy to have tv back , although the station and trucks are much cleaner when they are bored, If it acts up again I know what to check . Thank You again .

 

LeeMe, Your so welcome. If you ever have a samsung with a vertical problem D501 is usually the culprit there.



Fred