TV pincushion circuit repair

[omgwtfbyobbq]

Well, at least I think it's the pincushion circuit. The picture will bow inward from the sides affter the set has been on for a few minutest to a half an hour. Here's the really funny thing. If I shim the board inside w/ a large folded plastic zip tie, it will push the board up enough to reverse the behavior. The TV will instead start w/ the hourglass shaped picture, and then switch to the normal square picture. Does anyone know where I should look on the board or why flexing the board slightly is reversing the odd behavior?

 

[Nigel Goodwin]

It's most probably just a poor soldered joint (a 'dry' joint), you need to locate where it is, and resolder it.

It's finding it that is the hard part - but common places are on transformer pins, or on transistors mounted on heatsinks.

 

[krytenrobot]

Can you give us the model num of your tv so we can av a look at the manual?

 

[omgwtfbyobbq]

I'm away from home currently but I should be able to post the serial in a few weeks. IIRC I tried looking for it online (Admiral brand) but I couldn't find anything. Thanks for the advice Nigel!

 

[tvtech]

I'm away from home currently but I should be able to post the serial in a few weeks. IIRC I tried looking for it online (Admiral brand) but I couldn't find anything. Thanks for the advice Nigel!

Don't worry about a manual to fix a "dry joint". Just good eyes and patience. And a soldering iron and a little fresh solder.

Cheers

 

[8gokartracer]

cold or Bad Solder Joint

I will describe to you how I have always found bad Solder Joints on TV Circuit Cards.

You must be able to access the bottom of the main circuit card so you can take something like a plastic stick (normally used to adjust potentiometers. I usually call them dido stick or a plastic tweaker) and rake it across the solder joints on the bottom of the main circuit card while having the TV turned on. you will have to place a mirror in front of the TV picture tube set at an angle facing you so you can watch to see when the picture straightens itself up. You must be careful when raking the dido stick across the back of the circuit card so as not to touch the pins with your hand or fingers which might cause you to get shocked. When you hit the right pin or bad solder joint you will be able to see the picture fix itself. You will have to rake the dido stick in this area several times raking in a smaller area each time until you have located the exact pin that has the bad/cold solder joint. once you have located the bad solder joint it is a simple matter of heating the joint using a very small amount of Rosin Flux and adding a small amount of new solder to fix the bad joint. Be sure to remove any flux off of the circuit card using alcohol.

To access the bottom of the main circuit board you will have to pull it out of the TV stand it up on its end, leaning it against the circuit card that is connected to the neck of the picture tube. Be sure to insert a big piece of card board between the main circuit card and the card that is attached to the neck of the picture tube to insulate both cards from each other so they will not short or arc with each other. Of course you will have to hook up any wires you disconnected when you were removing the main circuit card. Be sure to use a Shorting probe if you have to disconnect the High voltage wire/suction cup wire from the Anode of the Picture tube. Be sure to reconnect this HIGH VOLTAGE wire/suction cup before applying power to the TV Once you have the main circuit board standing on its end so you have access to the solder joints on the bottom of the board and you have all of the wires reconnected, you will be able to put power on the TV and use the dido stick method I described in the 1st paragraph to find the bad solder run.

 

[tvtech]

I will describe to you how I have always found bad Solder Joints on TV Circuit Cards.

You must be able to access the bottom of the main circuit card so you can take something like a plastic stick (normally used to adjust potentiometers. I usually call them dido stick or a plastic tweaker) and rake it across the solder joints on the bottom of the main circuit card while having the TV turned on. you will have to place a mirror in front of the TV picture tube set at an angle facing you so you can watch to see when the picture straightens itself up. You must be careful when raking the dido stick across the back of the circuit card so as not to touch the pins with your hand or fingers which might cause you to get shocked. When you hit the right pin or bad solder joint you will be able to see the picture fix itself. You will have to rake the dido stick in this area several times raking in a smaller area each time until you have located the exact pin that has the bad/cold solder joint. once you have located the bad solder joint it is a simple matter of heating the joint using a very small amount of Rosin Flux and adding a small amount of new solder to fix the bad joint. Be sure to remove any flux off of the circuit card using alcohol.

To access the bottom of the main circuit board you will have to pull it out of the TV stand it up on its end, leaning it against the circuit card that is connected to the neck of the picture tube. Be sure to insert a big piece of card board between the main circuit card and the card that is attached to the neck of the picture tube to insulate both cards from each other so they will not short or arc with each other. Of course you will have to hook up any wires you disconnected when you were removing the main circuit card. Be sure to use a Shorting probe if you have to disconnect the High voltage wire/suction cup wire from the Anode of the Picture tube. Be sure to reconnect this HIGH VOLTAGE wire/suction cup before applying power to the TV Once you have the main circuit board standing on its end so you have access to the solder joints on the bottom of the board and you have all of the wires reconnected, you will be able to put power on the TV and use the dido stick method I described in the 1st paragraph to find the bad solder run.

Nice walk through there.

I have been in the TV repair game for yonks and can spot a "dry joint" a mile away. So to speak.....

On a CRT TV ....

1. Scan coil plug likes to go "dry jointed". Either Horizontal or Vertical line on your screen.
2. Heater pin on LOPTX likes to go "dry jointed". Picture slowly fades after TV has been on for awhile.
3. Vertical IC fails. Some TV's chassis show buggerall. Screen is blank. Others offer a clue as in screen shows a horizontal white line.

That's it folks

Cheers