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how do I fix an analog tv with a shrinkig picture?

it's an old zenith about 1995. The picture is shrinking
from top to bottom so there is just a thin
picture in the middle.if I hit the tv the
picture will go back to normal for a very
short time.

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lemonie6 years ago
When do they swich-off your analogue-signal?

L
framistan6 years ago
If you can solder... you can very likely fix this tv. First UNPLUG the tv from everything and put it on a table to work on. Let the tv sit for a few hours being unplugged to be sure the capacitors and picturetube have discharged their voltage. A few minutes of waiting is all you really need to wait... but we are being extra carefull so you dont get shocked. Take off the back of the tv and whatever other panels etc needed so you can access the bottom of the circuit board. Any component that looks like it has a bad solder connection, you need to re-solder it with plenty of heating from the solder iron to be sure the solder flows smoothly. Be especially sure to solder the pins under the flyback transformer... the vertical output transistor(s)... and any component that is sort-of-large-ish. The larger components are the ones that the factory wave-soldering machine doesn't heat up enough to solder properly those components. Be very carefull to replace all wires onto the same terminals they came off of. they are usually marked with matching numbers or you could use magic marker to give each connector a number and same number written under the connector. Be extremely carefull of the NECK of the picture tube. If you smack it accidentally with something it might crack and picture tube IMPLODE. As you can see, there are dangers to doing this so do this AT YOUR OWN RISK. If you are under age... be sure to get parents help to do this and don't attempt if you are without supervision. If you re-assemble the TV and it still does the problem, there is a 2nd method of finding the EXACT component causing the problem but it requires turning on the TV with the back removed. Then you place a mirror at the front of the TV so you can see the picture while you use a plastic stick to gently poke each component and watch the reaction of the picture. When you find a component that you touch and the picture expands or shrinks... then THAT is the component that needs soldering underneath. Occasionally this is caused by a metal shield that has an UNSOLDERED tab underneath the PC board also. When inspecting the solder connections, i would often just solder every suspected LARGE component regardless of how the solder connection LOOKS ... because sometimes you cant tell by LOOKING whether the connection is bad or not. see the picture for what a "bad-solder-joint" looks like.
bad_solder.jpg
The CRT MUST be discharged before working anywhere near the high voltage connection. It can hold it's charge for weeks not just hours.
. Thank you! And keep it grounded all the time you are working near it.
. You can find instructions on how to discharge a CRT on the Web.
NachoMahma6 years ago
.  IIRC, that means the flyback transformer is bad. It can be extremely dangerous (kill you kind of dangerous) to work on the flyback transformer; it's connected to the CRT which is basically a very large, very high-voltage capacitor.