Re: Need Help Fixing a Monitor

[rubywand@aol.com (RUBYWAND)]

In article <4m2m7p$sm@opal.southwind.net>, scottw@onyx.southwind.net
(Scott Weierich) writes:

>Okay, the dreaded "my monitor turned blue and nothing can be seen on it 
>but a blank blue screen" syndrome hit yesterday. I believe from posts 
>from Rubywand that this means that the blue choke went bad. I saw his 
>post (and have a hard copy of it now) concerning it and the detail for 
>saftey was much appreciated, but the problem is that I need a bit more 
>detail on the actual procedure of identifying the bad component (where on

>the moniter EXACTLY it is!) and what it specifically is, where I can 
>probably look to find a proper replacement part, and how exactly I can 
>also adjust the picture before putting the case back on. I seem to 
>remember reading an article many moons ago on this very same procedure in

>seom sort of periodical in the Apple II community, but can't seem to find

>theright publication or article. Any ideas? Thanks for your time.
>
>

     First, since Joe L. Walters has posted a message on a monitor repair
topic, it is probably okay to mention that he is the "J.L.W." who
contributed the info and 'picture' for discharging the HV anode lead.


     Regarding the all-Blue, etc. problem ...

    Another II user (who does not wish to be identified) emailed the more
detailed information below:

>>....
       1. The part that causes the problem when it fails is a "choke" or
"inductor" , it is mounted on a small circuit board attached to the back
of the monitor tube itself. This part looks like a small blue ceramic ball
with two leads coming out the bottom, and is color coded for 10
microhenries.
 
      2. There are three of these items on that circuit board, and if any
one of them fails, the symptom is a screen all of one color, with total
loss of any controls of the monitor. The parts are identified by number,
and what color the screen is will tell you which one to replace.
 
       L6R2 for a Red screen
       L6G2 for a Green screen
       L6B2 for a Blue screen
 
     3. You can probably get a 10 microhenry choke at Radio Shack, or it
is available for $1.28 (plus a $5 Handling charge) from Digikey
Corporation
at (800) 344-4539.  They take Mastercard, Visa, and C.O.D.
 
     The Digikey part number is M8025-ND.
 
     4. After replacing this part, the monitor colors will need to be
readjusted via the small color trimpots on the same circuit board. ....
<<

     and, some additional adjustment info ...

>>....
This is what some of the RGB pots are:
 
R13 RGB Intensity
C86 Horizontal Position on RGB
C85 NTSC Color Hue Adjustment
C45 NTSC Frequency Adjustment
....

How does one go about adjusting the focus on a blurry GS RGB Monitor?
 
Just take the screws out of the back and slide off the back and locate the
pot labeled SCREEN at the back.  Then twist until you like what you see.
....
<<

    Evidently, "SCREEN" is the control I call "Focus".

    The 'Mini-Manual includes ... 
>> 
    Before putting the case back, this is a good time to adjust base
Intensity and Focus (the two nub controls on the HV module).  Position the
monitor so that screen is easy to see and the nub controls are accessible.
Plug in the the C/S Module. Adjust the C/S Module controls to center
positions. Plug in the monitor to the computer. Get a Desktop display with
some text and icons. Use an insulated tool to adjust the nub Intensity and
Focus controls for maximum sharpness at 'normal' viewing intensity. A
magnifying glass is helpful to obtain max pixel sharpness. 
<<

    When the 'bad' choke is removed, you can check it with an Ohm meter.
It should read as 'open' (very high R value).

    The reason your screen turns all-Blue (or all-Red, ...) is that the
blown choke prevents control voltage from reaching the transistor which
regulates the particular Color's intensity level. Your Blue transistor is
permitting Blue to run at max and, so, Blue swamps the display.

    When I did this repair for our monitor, just winding 20-25 turns of
small-gauge enamel-insulated wire (like #30 "magnet wire") on a
pencil-size ferrite core worked fine.    

Rubywand