Re: AppleColor RGB Monitor --- Problem

[mjmahon@aol.com (Michael J. Mahon)]

Quadrajet1 wrote:

>  Bad flybacks don't cause a single line problem, that's usually a bad HOT
>circuit problem.

The flyback _is_ the horizontal output transformer, as well as the high
voltage transformer.  A failure in the flyback like an intermittent open
in the secondary will produce a vertical line display.

Most horizontal output circuit failures result in no drive to the flyback,
which eliminates the high voltage, and therefore no display is visible.

In the case described, where the failed display was a single
_horizontal_ line, that indicates a failure in the vertical drive
circuits, not the flyback, though vertical output circuits may
be near enough to where the OP was spraying that it was
affected by the spray and "fixed" the problem for a while.

When you see a raster that is shrunken or a line, remember
that the dimension that is normal is the stage that is working,
and the shrunken dimension is the stage with the failure.

In many monitors, the vertical output stage is partially powered
by "boost" voltage generated by the horizontal output stage,
so anything that hurts the boost will also deprive the vertical
stage of proper power.  Conversely, if the vertical stage has
a fault that increases the load on the boost power, the horizontal
stage and the HV may be dimished, as well.

If the raster becomes slightly dimmer and larger, often fuzzier,
particularly as brightness in increased ("blooming"), it means that
the HV is low, since a lower HV makes a slower and more easily
deflected electron beam.

Since it is no longer economic to repair most TVs or monitors,
the skills to diagnose their problems are becoming rarer. ;-(

-michael

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