Re: How may I fix my Apple IIGS monitor?

[Rubywand <rubywand@swbell.net>]

Supertimer writes ...
> 
> The symptom is no image except a single horizontal line
> at the center of the CRT.
> 
> How may I fix this?  Has anyone had this problem?

 ....

     Several years ago, our monitor display would flick into a single
line from time to time. It turned out that the High-Voltage Flyback
transformer had one or more loose pins.

Note: The HV Flyback transformer is the black thing near the back left
side of the main circuit board. It has the Focus and Intensity controls
mounted in it and a fat lead running to the anode of the CRT (picture
tube).

     Unfortunately, the holes into which the HV Flyback transformer
mounts on the board are too large for the pins. So, each pin is
surrounded by more solder than is usually rquired for connecting
something to a board. Sometimes, this solder fractures-- i.e. develops
cracks-- and the connection between the pin and the circuit board is
disrupted.

     The cure was to resolder all of the HV Flyback transformer pin
connections using good quality solder (something like Kester "44" rosin
core 63-tin alloy solder).

     Naturally, there is a high-voltage shock hazard to consider even
with the monitor OFF and unplugged and allowed to sit for a day before
beginning work. Another hazard is the picture tube-- Do Not Break it.
Here is some info on safety and setting up to work on the monitor ...


>>

     Basically: unplug the monitor and let sit for a day, wear goggles,
work on a non-conductive table surface, do not stress CRT neck.

     Unplugging the monitor and letting it sit for a few hours reduces
the danger of shock from stored charges; it does not eliminate it. The
usual warning for this kind of work is AVOID touching two different
circuit points at the same time. Like, don't touch the metal chassis and
the conductive surface of the CRT at the same time.

     WEAR protective GOGGLES. If you should, somehow, bump or stress the
CRT neck-- as in jumping when you get shocked-- it may break. The result
may be a peaceful THOOP! or the CRT may implode in a spray of glass.
(Avoid using the CRT's neck to support the monitor in any position.)

     Work on a wooden or plastic-topped table with plenty of space. Try
to position yourself, tools, and the monitor so that when you get
'stung', the chances of breaking something are reduced.

     As much as posible, avoid using heavy tools of any kind. An
inadvertant tap from a mini-screwdriver is much less likely to crack the
CRT than a bonk from a full-sized screwdriver or pair of pliers.

     Rubber gloves are probably a good idea so long as they do not get
in the way. Of course, pointy connections and components can puncture
gloves.

     It's a good idea to clip a wire to the chassis and touch the other
end to the conductive surface of the CRT a few times before doing any
work in order to drain off any charge there.

Note: Several places in a monitor or TV carry high enough voltages to
deliver an uncomfortable shock. Draining the charge from one point does
not guarantee that other points have been discharged.

===========================


From: Joe Walters

004- How do I discharge the High Voltage?

The HV charge (20,000+ volts) might not be much reduced by just waiting
a few hours (or days), especially if you are in a low humidity location
and the tube, etc., are all of good quality.

1. There is a long wire (called the anode) that goes from the high
   voltage power supply to the top of the tube where it is snapped
   into a hole. You can't see the hole because there is a rubber
   shield built onto the wire. The end of the wire goes to a metal
   clip which, without the rubber shield, looks somewhat as below.
   One squeezes the clip so the end slips into the hole in the tube.
 
   ---     ---
  ==  \   /  ===== back of CRT
       \ /  <-- metal clip (This is what your grounded
        |                      screwdriver needs to touch.)
       [|]
       [|]  insulated Anode lead going to HV module
       [|]

   Needless to say, UNPLUG the monitor before beginning. Simply
   turning it off isn't good enough.

2. Get a clip lead and clip one end to a long slender screwdriver

3. Clip the other end to the metal chassis of the TV  (i.e the
   metal frame parts)

4. Carefully! slip the screwdriver tip under the rubber flap on the
   top of the tube until it touches the internal wire that both
   holds the anode wire in place and conducts electricity.

Step 4 may result in a somewhat loud "SNAP" as the tube is discharged.
Be prepared so you don't jump and break something.

===========================


From: Rubywand

005- How do I open my RGB monitor's case and get set for doing
     internal adjustments or repairs?

     Whatever it is you plan to fix, if you remove the monitor case, you
will probably need to unplug the cable running from the circuit board to
the Controls/Switch Module on the side of the case. Use 'whiteout', 
nail polish, etc. to mark the position of the plug. In more detail ...

   1. Unplug everything from the monitor & let it sit for a day.

   2. Put on protective GOGGLES. Place the unit face down on a wooden or
plastic-topped surface with lots of space and good lighting. Remove the
the screws. Place the unit in nomal position.

   3. Have a fat magazine ready. Slide the case off until you are able
to see the control leads plugged into the main board on the right side
of the case. Mark the plug position with 'white-out', nail polish, etc..
Unplug the connector.

   4. Slide off the case while supporting the monitor and slide the fat
magazine under the circuit board to prop up the monitor from behind.


   5. Discharge the HV (optional, but, generally, a good idea).

   6. <Do adjustments, fixes on Monitor>

   7. When done, reinstall the control assembly.

   8. Still wearing GOGGLES, support the monitor, remove the magazine,
slide on the case, reconnect the plug, finish sliding on the case,
replace screws.

= = = = = = = = = = = = = =


006- What tools and solder should I use for repairs?

     For any soldering use a good quality pencil-style iron rated at
25-40 watts with a holder and sponge. Use high quality (60/40 tin/lead
or better) rosin core solder (e.g. Kester "44" 20 gauge).
    
<<


     There are other possible causes for a flat lined display. However,
a loose HV Flyback transformer connection is a well-known source of
trouble for this monitor.



Rubywand