Question about Quasar SP-2725 27" TV
We acquired an older standard type Toshiba TV that the kids use for Wii. It seems to have problems after it warms up. The screen goes black. There is also no sound when the screen goes black. The picture (along with the sound) often comes back when you hit the TV. It seems to be getting worse. Is there an easy, inexpensive fix we can try?
This could be due to what we techs call a 'cold solder joint.'
The mere fact that temperature and whacking the
set seems to help, reinforces this diagnosis.
There are a number of points on the circuit board that get quite hot and solder joints can fail from metal fatigue; the swelling and shrinking of the joint until the copper leads and solder (tin/lead) separate.
To inspect the main board, please pull the plug from the AC and let the unit sit overnight to eliminate the chance of a nasty shock, then remove the back (~6-10 screws).
If you have a digital camera make a couple of pix of the guts from different angles unless you trust your memory, then pull plugs from the board (marking them in some way is best).
The heavy-looking lead attached to the picture tube (CRT) has a spring clip that needs to be compressed from the side to free it, otherwise the various cables can be removed by unplugging.
You should have a quality soldering iron for this, NO GUN! These are too hot and may cause the traces on the PC board to lift. The soldering tool needn't cost a hundred bucks but should be designed for electronics work, preferably with an iron-plated copper tip; these stay clean better and are easier to tin. The solder should be some designed for electronics use (no acid!) and with a rosin core that serves to clean the surfaces to solder. In the same place, pick up some 'solder wick' or if they have cheap solder suckers, any of these should be good enough unless you are planning on doing this for a living. The total cost will be under ~ $20 US.
You should have a cellulose sponge, wetted and wrung out so you can often clean (wipe briefly) the tip and put fresh solder on it.
Now you are kinda prepared (40+ years experience is better) to look for solder joints on the underside of the board. If a joint, especially a larger one (they are more sensitive) that appears dull or even cracked around the pin coming through from the other side, use the wick or ****** to remove the old solder, clean the tip, flow some of the new solder into the joint. It should look shiny and obviously flow onto the pin and the board joint. Try to keep the length of time short; otherwise, the trace may lift from the board. If it does, use something non-metallic and heat proof to hold it down, reheat the solder joint briefly and press the trace down onto the board again with the tool.
If you cannot identify any specific joint that might have failed, I would recommend you do all except the smallest ones (called shot-gunning) so you have some chance of hitting the right one.
You can do this! Just think, you've learned a new skill! Unfortunately, it isn't one particularly valuable anymore since we now just throw stuff away instead of trying to compete with Chinese child-labor.
Posted on Jan 15, 2009
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