12 Mar
2004
12 Mar
'04
5:36 a.m.
This is fixable. It is caused when some material is
magnetized. The process to fix it is called
'demagnetizing'. The theory is simple: You apply a
changin magnetic field (for example, that created by a
coil with 60Hz AC), and graduately decrease the
strength of the magnetic field (for example, you pull
the coil further away from the monitor while moving it
in circle). It will fix the problem. Some monitor or
TV has build in circuit to perform the process.
In my experience, this is a lot trickier than it
sounds. I would
first practice on a CRT that you aren't fond of before moving on to
the one you're trying to rehabilitate.
Coils for CRTs are wrapped in electrical tape and shaped to suit to
hug the CRT. Electrical tape they used can be any color, rarely see
one with off the beaten trail color like yellow, blue etc.
In tritron CRT monitors especially high end, it has many coils around
the back of CRT, one is degaussing, at least 2 thinner coils for
purity compensation, one round coil near CRT yoke for
picture rotation (common to many monitors also found in some direct
view TVs.)
Sounds like the purity compensation circuit isn't working, check that
your monitor compass module is working. Yes there are few monitors
has one uses it for automatic purity adjustments when monitor is
facing in different direction.
How I know? Fixed an high end sony 21" monitor with that feature.
It was bad compass module IC, more precise, a pin corroded off, fixed
that by grinding away black package and solder short strand of to
make connection. Compass module board is usually horizontal and
almost centered where the base axis is.
Cheers,
Wizard
--
Sellam Ismail Vintage Computer Festival