jpdylon
08-20-2008, 05:42 PM
Wondering if someone can point me in the right direction.
When the set is cold the horizontal hold is very touchy and will sometimes start tearing. After a couple of minutes the set has a steady picture, but there is a pie crusting problem. The pie crusting effect doesn't get worse or better as the set is left on.
It appears that the horozontal output and driver transistor were replaced, perhaps to try to cure the problem. THe HOT is a philips part 433-2 - which I believe to be an original replacement part. The driver transistor is an NTE198. What was the original supposed to be, and would it have an effect on the pie crusting problem?
Your thoughts, ladies & gentlemen?
firenzeprima
08-21-2008, 12:54 AM
uuhhmmm seems a problem of thermal drift, try to control the electrolytic capacitors and tin solders circuits concerned
radiotvnut
08-21-2008, 01:12 AM
I'd scope the B+ lines to the horizontal oscillator and driver circuits to see if there was any trash on the B+ lines. I'd also check the regulated B+ feeding the flyback and horizontal output circuit to make sure it was regulating and free of ripple or other garbage.
The newer Philips / Magnavox chassis had a 100uf, 200V cap in the 130V B+ line that would fail and cause horizontal sync problems.
jpdylon
08-22-2008, 11:27 AM
ok, there were some small electrolytics in the oscillator section that were leaky. The tearing and piss poor sync problems are now gone.
The remaining problem is jagged vertical lines. Its not so much a pie crusting effect because its uniform all over the screen. I may post some screen shots if possible. B+ lines are clean and it happens on both tuner and AV. Definitely noticeable on the OSD.
kx250rider
08-22-2008, 12:05 PM
Those has some weird problems in the IF & AGC circuits that cause problems maybe similar to what you're seeing. It's been 10 years since I worked on one of those, but I seem to remember replacing a crystal filter (tiny blue packaged part under one of the shield cans :( ) If you have trouble with it, I can try asking my friend Bob in West LA. He's a Magnavox whiz-bang tech.
Charles
jpdylon
08-22-2008, 11:40 PM
I got a slight clue as to what it may be. The vertical height was a little lacking when I fired upt he set this evening to do some more troubleshooting.
Here are some screen grabs. As you can see its almost as though just a few scan lines are shifted to the side. They move about randomly. Perhaps its actually a vertical failure....:scratch2:
The problem DOES NOT worsen as the set warms up.
http://i49.photobucket.com/albums/f298/AKjpdylon/magnavox/P1010008.jpg
http://i49.photobucket.com/albums/f298/AKjpdylon/magnavox/P1010009.jpg
http://i49.photobucket.com/albums/f298/AKjpdylon/magnavox/P1010010.jpg