Re: Monitor Problems

[supertimer@aol.com (Supertimer)]

Paul Grammens <pgrammen@sonic.net> wrote:

>Supertimer wrote:
>>
>> I've got one for you, Paul.  My IIGS RGB monitor now only displays
>> a horizontal line across the center of the screen.  I've flipped through
>> PC Tech books and discovered that this is a common problem and
>> that "the vertical deflection is faulty" or something like that.  What
>> does that mean and is it expensive to fix?
>
>You are correct, it is the vertical circuit that is the problem. I
>jumped up, ran to the garage, zipped the screws out of my spare IIgs RGB
>and took a look. I can't tell you exactly what the problem is, but I can
>tell you where to look. With the back off and viewed from the rear, note
>the 4 wires running from the neck of the tube to a connector on the
>board. The red/blue wires are the horizontal deflection signals going to
>the coil on the neck, and the yellow/brown wires carry the vertical
>deflection signals. Vertical deflection starts with a vertical sync
>signal coming from the computer and ends with a powerful sawtooth signal
>going up the yellow/brown wires to generate a magnetic field in one of
>the coils around the neck. So the problem lies between those two points,
>and the most likely culprits are:
>
>1. Cracked solder joints. Use a magnifying glass to look for these,   
>following the path of the signal.
>2. Blown transistors, diodes, or IC's. Sometimes you can see (or
>smell)    which one is gone. Also study the board for burn marks or
>discoloration    from heat. That is often the way I find the culprit.
>3. Bad capacitors. They can be tough to find, unless they got hot.
>4. Open resistors- often will be burned or discolored, but not always.
>
>Looking at the underside of the board, it looks like Q401, Q402, and
>IC401 are all involved in generating the vertical sweep, so focus on
>that area. The vertical sync signal goes from the external connector at
>the rear to the board that plugs onto the end of the tube. It runs
>across the board to a connector on the right side (viewed from the rear)
>and then by a wire to the main board. IC401 probably generates the sweep
>signal, and transistors Q401 and 402 probably amplify the signal to
>drive the coil. 
>
>So: Be safe, leave it off for a while before you open it up. Stay away
>from the fat red wire going to the tube, it's the high voltage. 
>Get some bright light and a good magnifier (I use a small hand lens with
>two 5X lenses that can be added for 10X, available at nature stores).
>Use your eyes and nose, follow the signal path looking for cracks and
>burns. 
>A digital multimeter (some cost less than $20) is a good tool for
>checking for opens and shorts. Get one with a diode checker, diodes
>should measure .5 to .7 volts in one direction, off the scale in the
>other. Transistors can be tested like two diodes base to emitter, and
>base to collector. Blown transistors and diodes can either be open or
>melted into a short. 
>
>That's kind of a thumbnail tutorial on the art of troubleshooting using
>only the cheapest tools, and power off.  I also measure the voltages and
>signals with power on, but that is beyond the scope of this. 
>Good luck, and glad to find some way to help you, considering how often
>you have shared your knowledge of Apples with me.

Thanks for the info, Paul!  I opened the case and took a look at the
bottom of the base circuit board.  I don't see any cracked solder,
but I do see discolorations here and there.  In fact, it looks like
some component(s) leaked.

One thing I do notice is that some time ago, when the screen
began to exhibit symptoms (at that point, the vertical would shake
and stabilize after the monitor warmed up, followed progressively
by longer and longer collapses to a horizontal line until one day,
the monitor no longer recovered), I followed the instructions in
the monitor repair FAQ and resoldered the big holes in the HV
module.  Today I noticed that these holes were discolored and
some white encrustations enveloped some of them, almost (or
maybe even) reaching to neighboring solder connections.

Did I do something wrong?  Does one have to clean a solder
connection that was made using rosin core flux?  I sort of just
soldered the connections and closed the case.  Now I fear that
the white encrustation is conductive and may have precipitated
the end.