N
NTK
- Jan 1, 1970
- 0
Hi there! I've been reading the posts on verticle problems,
particularly on JVC TVs, and have come up short fixing my TV. One
evening recently, the TV suddenly developed vertical foldover at the
top. There was no for-warning to this.
After reading many posts, I tried first to resolder the vertical chip
(TA8432K) and surrounding components. I then replaced the boost cap
(100uF 35V 105C)and the pair of 470uF 35V caps in series with the
yoke. I've checked the boost diode and 70-ish volt zener (no
schematic, so I'm not certain what the voltage rating of the zener is)
and neither one is shorted or open. I'm seeing about 12 volts DC on
the low voltage vertical supply, and 27 volts DC on the "high" voltage
vertical supply (with 1 volt AC ripple on my VOM). The boost cap gets
charged to about 26V, but doesn't appear to ever discharge (0 volts AC
voltage reading on my VOM).
I only have a VOM to troubleshooting (though I'm borrowing an o'scope
this weekend to view my waveforms).
I also noticed that the verticle pincushion is slightly off--easily
seen on letter boxed DVDs. For a scan line above the center of the
screen, the left and right sides of the scan are above the center,
though only slightly, but enough to give it a very slight bowl shape.
So I'm left with several choices (as I see it): the ramp is bad, the
vertical IC is bad, or the vertical PS is wobbly (bad filter caps?
that's my next check once I get the scope). The ramp is generated by
the vertical IC, btw. I swapped out the ramp cap, too, with no
change.
Any help, insight, or assistance would be GREATLY appreciated.
Thanks!
Nathan
particularly on JVC TVs, and have come up short fixing my TV. One
evening recently, the TV suddenly developed vertical foldover at the
top. There was no for-warning to this.
After reading many posts, I tried first to resolder the vertical chip
(TA8432K) and surrounding components. I then replaced the boost cap
(100uF 35V 105C)and the pair of 470uF 35V caps in series with the
yoke. I've checked the boost diode and 70-ish volt zener (no
schematic, so I'm not certain what the voltage rating of the zener is)
and neither one is shorted or open. I'm seeing about 12 volts DC on
the low voltage vertical supply, and 27 volts DC on the "high" voltage
vertical supply (with 1 volt AC ripple on my VOM). The boost cap gets
charged to about 26V, but doesn't appear to ever discharge (0 volts AC
voltage reading on my VOM).
I only have a VOM to troubleshooting (though I'm borrowing an o'scope
this weekend to view my waveforms).
I also noticed that the verticle pincushion is slightly off--easily
seen on letter boxed DVDs. For a scan line above the center of the
screen, the left and right sides of the scan are above the center,
though only slightly, but enough to give it a very slight bowl shape.
So I'm left with several choices (as I see it): the ramp is bad, the
vertical IC is bad, or the vertical PS is wobbly (bad filter caps?
that's my next check once I get the scope). The ramp is generated by
the vertical IC, btw. I swapped out the ramp cap, too, with no
change.
Any help, insight, or assistance would be GREATLY appreciated.
Thanks!
Nathan
