Re: My RGB went green!

[dynasor@infi.net (Dennis McClain-Furmanski)]

Ron Louie (ronlouie@u.washington.edu) wrote:
: Now which pocket do I put which hand in.....breast pocket, pants pocket 
: or pocket socket?? };)  jes' kiddin'

: Thanks for everyone's replies, including Petar and Tony (from Alltech).  
: I'm awaiting my Sony, while using another Green Screen, pirated from an 
: office IIc!  I guess I'll try to fix it, and donate it to the local 
: elementary school ( I already gave them my lovable IIe, my 300 baud 
: modem, and my 40Meg PowerDrive with JumpStart installed!)

Don't give up yet. Try this.
=====

A reprint from the archives of The Road Apple, 1991:
 
All Green can Give you the Blues and Make you See Red
by Dennis McClain-Furmanski
 
   This article gives a complete description of a problem which
is becoming increasingly common with AppleColor RGB monitors.
This is the current monitor which comes with the IIGS, not the
AppleColor 100, which has been discontinued.
   Techie warning! This is a technical problem, and calls for
experience with electronics. While you might not be able to
handle the work yourself, it's highly likely you can find someone
experienced enough with a soldering pencil to save you a great
deal of money. The instructions will be clear enough to anyone
with board level repair experience. If you've experienced this
problem, give them this article to work from. They shouldn't need
anything else except one small part and soldering equipment. And
a safety tip: you MUST do this with the monitor unplugged.
Preferably after having it sit for a day or two to drain off the
enormous charge in the CRT. It can bite, even after days of not
being used.
   I had just rebooted when out of the blue, everything went
green. Not just shades of green, but an all encompassing,
pervasive green. No image, no brightness control, nothing. Just
an eye piercing solid green screen. Being an unabashed techie
with some experience in things video, I opened my RGB monitor to
see what I could see. It was just some huge amount of stuff. I
was out of my league and I knew it. But what to do? A motherboard
swap for an Apple RGB is costly.
   Luckily, if I can stretch the intent of the term, I was not
the only one in this situation, and someone who'd experienced
this same problem was much better at these things than I. Donald
Beaty, AFA DonB on America Online, is a retired physics
professor. He had had the same symptoms and had been able to
discern the cause. Virtually all of the information I'm about to
impart is his doing. It is due to his experience and hard work
that I'm able to type this without blinding myself with a
composite monitor, and can afford my weekly pizza. Thank you,
Don.
   An RGB monitor is only somewhat like a TV or other composite
monitor. The RGB handles the red, green and blue signals
separately. Not mixing them gives the monitor the ability to
produce a sharper picture. Each of these signals must be
amplified so that they can be used to produce the picture. One of
the two boards in an RGB monitor hangs on the back of the CRT or
picture tube. It contains the circuitry to drive the CRT. Among
the components are three transistors, labeled Q6G2, Q6R2, and
Q6B2. Q is for transistor, the 6 is for which component in the
circuit, and the R, G or B is for the color it handles. These
transistors are relatively large rectangular black slabs, about
1/4 inch by 1/2 inch. They have three legs going through the
board, and are mounted against steel braces on the board which
serve as heat radiators.
   Just above these transistors are small blue blobs on two legs,
each with a black and a red dot on them, and numbered identically
to the transistors except the first letter on the board next to
them is an L. These are called inductors or chokes. They're for
keeping the sharpness in that color. The problem stems from the
one marked L6G2, above the transistor Q6G2. It seems these are
failing fairly consistently. Since they're going bad, but the
others in the circuit are not, it is likely that the problem is
mechanical, possibly resulting from a misaligned manufacturing
machine in the factory. They have probably been jammed or twisted
in the process of building the monitor, making them weaker and
liable to breakdown.
   To repair your monitor, first unplug it completely. I
recommend doing so days before you attempt the repair, unless you
know how to drain off the residual voltage from the CRT anode. If
you don't know how, I'm not going to tell you, because it's
dangerous. Just let it sit for a few days.
   Take the back off the monitor by removing the four screws, two
on top and two on the bottom, from the rear. Carefully slide the
back off. You can feed the power cord in though the hole in the
back. Make sure you don't pull too hard or too quickly, as the
power switch is connected to the side of the back portion, and
the wires to it are still connected. Once the back is off far
enough, move it to the side so you can see the back of the board
hanging on the back of the CRT. From above, you can see the parts
described above, and from the back you can see the numbers on the
board corresponding to the parts. The part L6G2 is marked with a
small line between the two solder connections and the numbers
right next to them. If you're having trouble locating this, from
the rear of the board, it's at approximately 10 o'clock from the
center of the board, about half way to the edge.
   There's always the slight chance your problem has a different
cause. To test this, it's necessary to power up the monitor. This
is NOT for the inexperienced. With the choke defective, the
screen is solid green, even with no input. If you short across
the legs of the choke, the screen should go to black. If it's
still green, you have a different problem and I can't help you. A
second way to test it is with a voltmeter. If there's about 100
volts of potential across the legs of the choke with the monitor
on, the choke is open, and this repair is for you.
   To remove the part, heat the solder pads at either end of the
line between them. You can use solder wick or a solder sucker, or
just heat the pad and pull the part out from the other side with
needlenose pliers. Some people like to clip the part off of the
legs, and pull them out later. I never do, because I've been
known to try to remove the wrong part.
   Once you get the part out, you'll need a replacement. You can
go to most any electronics supply store (maybe even Radio Shack,
but no promises) and get a replacement choke. The original is a
"20 micro-Henry choke". You can try asking for that. This is a
non-standard value, but it's worth a shot. If they don't have
one, the nearest standard value is 22 micro-Henry. I've used
this, and it works fine. Don't be concerned if the replacement is
not shaped or sized like the original. As long as the specs are
right, it'll work.
   Now, simply solder the part in the place of the old one and
reassemble the monitor. Be certain you haven't dragged solder
between the pads, and that you've trimmed excess leads from the
part from the back of the board. If all has gone well, you've
just saved yourself what Don states was quoted to another
sufferer of The Green Disease as a $315.00 repair bill.
 
 
Follow-up: A year later, within two weeks of each other, the blue,
then the red went out. Same problem, same fix. Just change the
chokes marked B and R instead. Save yourself some time, spend
the extra $4.00 now for the other two, and replace all 3 at once.
At $2.00 each, and maybe a 30 minute repair time for all 3, it beats
buying a new monitor or daughterboard.

--
dynasor@infi.net                                       The Doctor is on.