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Most probably the vertical deflection amplifier is failing. The most common part that fails is the vertical output transistor. The set is too old to find documentation on part numbers and descriptions. Probably the part is no longer available and you will need the assistance of someone who can help you find an equivalent transistor that will do the job. Of course, without testing we cannot be certain the failure is the output transistor. It could be from something else such as the voltage regulator that feeds the dc line to the vertical section. Could be the vertical synchronous level that goes too low to trigger the vertical sweep generator.
Other bad parts in vertical deflection circuit though there are not that many parts that would kill the deflection entirely.
Loss of power to vertical deflection circuits. Check for blown fusable resistors/fuses and bad connections.
Loss of vertical oscillator or vertical drive signals Good luck.
There is a failure in the vertical deflection circuit. Typically there is a vertical output i.c. that provides the deflection vertically. The i.c. itself is a fairly common component to fail. There are some lower power circuits that feed this output device that also could be the problem. When the electron beam in the tube is not deflected vertically it "writes" only horizontally across the center of the screen thus resulting in a single trace. Be careful not to leave this at high brightness for any extended time as it can "burn in" that area of the screen. Unless you are a "techi" this is a job for a qualified technician. Troubleshooting would be in the vertical deflection section of the set. Most of the parts are not expensive in themselves, except for the deflection yoke which sits around the neck of the tube. The cost to repair would typically be the shop labor.
This denotes a problem with the vertical deflection circuit. This is more then likely the result of the vertical coupling capacitor failing. You will need the schematic diagram of the TV to find the capacitor in question. it is located between the vertical output stage and the vertical deflection winding of the yoke transformer. In addition check the continuity of the vertical winding of the yoke transformer this can cause the same problem. In any event the problem is that the vertical deflection signal is not getting to the yoke transformer or the yoke transformer is malfunctioning.
As far as I can recall, this set uses a standard vertical IC. Check that first. It should be an LA7837 or somethint similar. Also, check the capacitors in the same circuit as well as the supply voltages to the chip. If that fails to resolve the problem, please update this and we'll move on to other areas.
If you mean a horizontal line going left to right across the center of the screen and it's intermittent then a tech should be able to fix that one on a service call fairly easy... The vertical IC in that unit, IC N301, is a TDA8351 and it most likely has some poor solder connections due to heat stress - we call ring cracked - thus the problem sometimes corrects itself temporarily.
While he's coming out anyway ask him ahead of time to bring the following:
Two resistors 1.0 ohm 2 watt
and a cap 3300 microferet 25 volts
and his DMM & ESR meter.
Ask him to ESR test C863 this is a high failure cap and test R370 & R371 in the supply for change in value.
Shouldn't be too much to repair - and simply ask ahead of time what they charge for a service call, and if they think they can correct such a problem (ring cracks on the solder connections of your vertical IC) on-site.
If you're not too sure where to begin your research for a qualified shop try NESDA at:
Sounds like the vertical control IC has gone out. Replace IC N301 (TDA8351) and check or replace R370 (1ohm), R371(33ohm), and R380(1ohm). This shouldn't affect the sound but once you get video you might figure out what is wrong with the sound (control setting).
The TDA8351 crosses to NTE7156 and shouldn't run you more than $10.