"It isn't easy, being green..."  
                               Kermit, ca. 1982

I'd started to think my Apple 2GS RGB monitor was immortal.  It had always worked
for me just as it did when I first turned it on in 1987 or thereabouts.  Then
without any precursor warnings my monitor's screen lit up with a hurt-your-eyes
green raster and no video.  50-dollar bills flashed before my eyes.

I'm no stranger to tv servicing, so there was no question but that I 'd give it
my best effort before spending the big bucks for repair or replacement.  I hit
the wall without service data.  The local electronics-supply dealer told me,
"Nah, there is no Sams Photofact for the Apple 2GS monitor...  Apple never did
sell many 2GSs, so Sams didn't do anything for the 2GS!"  I drew myself to my
full height, started to tell him about the millions of Apple 2GS computers still
in use then said, "Ok..." and left the store.  I'm tired of arguing the point.

I made my own Sams by tracing out the pc-board circuitry.  A boring but necessary
step.  The paper schematic helped to make sense out of the voltage readings on
the pc board's various test points.

The excess greenness was the result of an open peaking coil.  Peaking coils are
small inductors used to extend the frequency response of video amplifiers.  A
transistor amplifier has unavoidable capacitance that bypasses high-frequency
video components.  It's these high-frequency signals that enable the CRT to
change brightness quickly as it forms sharp edges.  Inductance, such as that
found in a peaking coil, cancels capacitance.  If you choose just the right
amount of inductance you can compensate for the unwanted capacitance, which is
exactly what happens when a peaking coil is doing its thing.

The open inductor in my monitor's circuitry allowed the green cathode on the CRT
to drop about 100 volts lower than normal, and this action biased the green gun
into saturation.

It was obvious that something was amiss once I'd determined that the peaking coil
had100 volts across it's terminals.  I had two good peaking peaking coils for
comparison in the red and blue circuitry.  Each of these good coils measured
about 10-ohms resistance.  The flakey coil was open.  Shorting the open coil for
a test eliminated the excess green on the screen but at the expense of poor green
bandwidth.

How do I get a replacement peaking coil?  The local electronics supply dealer was
about as helpful as he'd been with the Sams Photofact deadend.  "Peaking coils
almost never fail.  You have to go back to the manufacturer to get a replacement!
 Forget it!"  This time I stood up to him, asked to see his stash of peaking
coils.  I needed a 20-microHenry inductor,  and he did have a 22-microHenry unit.
 $1.95.

The 10% excess made no noticeable difference and my monitor seems as good as new.

Being green is not so bad if your monitor can also be red and blue.