Re: Monitor help??

[Rubywand <rubywand@swbell.net>]

TomMage writes ...
> 
> The monitor I am using with my ][e is malfunctioning, it is a Magnavox RGB by
> the way (looks almost just like my Commodore 1902 monitor :) ). The picture
> just starts fading away until the screen is blank. If I whack it a couple times
> the picture comes back for a while, but then fades again. Is this baby on it's
> last legs or is there something that can be fixed (without having to throw it
> against a wall or something? :) )
>

 ....

     Since, evidently, bonking temporarily restores contact, it sounds
like something is loose or making poor contact.

     A fairly good bet is a dirty control (intensity or focus) or a
loose connection of the High Voltage anode lead to the CRT (picture
tube). A bit less likely is a loose component.

     Probably, you are going to need to get inside the monitor. There
are several hazards here. One is breaking the neck of the CRT and
getting sprayed with glass (wear goggles); another is getting zapped by
a stored charge which may run from a few hundred Volts up to several
thousand-- i.e. even with the monitor OFF and unplugged.

Note: If you are new to monitor repairs and have a friend with
TV/monitor repair experience, it is a good idea to ask him/her to do the
inside monitor stuff and watch.

     The simplest guideline for avoiding shock-- after unplugging the AC
lead, moving to a nice open wood table or similar non-conductive work
area, and letting the monitor sit for a few hours-- is to not touch two
conductive surfaces at once. Like, don't hold the metal chassis (or
anything metal on the monitor) and mess with the anode lead. Rubber
gloves may be helpful but they do not guarantee protection.

     Hi Voltage charges can exist in a monitor for days after all power
is removed. The usual danger from getting shocked by a monitor is what
you do in response-- for example, plow through a window, fall off a
stool, smash a tool into the CRT, etc.. For sure, keep any heavy metal
tools away from the monitor.

     Basically: Be Careful. Make sure it is unplugged (e.g. have the AC
plug in view with, maybe, masking tape wrapped around it). Keep an
opened monitor away from the reach of children, ... . The newsgroup FAQs
file Csa2Monitor.txt goes into a bit more detail about safety. You can
find the file at ...

for Viewing via an FTP program or for downloading ...
 ftp://ground.ecn.uiowa.edu/apple2/Faqs/

for on-line perusing via Netscape, etc. ...
 http://www.grin.net/~cturley/A2.FAQs.and.INFO/CSA2.FAQs/
 ftp://apple.cabi.net/pub/applegs/FAQs.and.INFO/A2.Csa2.FAQs/


     One good try at a fix includes squirting Radio Shack Control
Cleaner into controls and turning them back and forth. Try to mark the
control's position first and return it to this setting after squirting
and turning it. (The cleaner needs to get _inside_ pots and switches to
do any good. On a monitor, some pots will be open; other's will have a
metal cover. You can get inside of most metal pot covers from the place
where the leads come out.)

     Another try is blowing/whisking dust from the CRT and High Voltage
module (using non-conductive brushes) and slightly twisting the Anode
lead where it clips into CRT to reestablish good contact. The HV module
is the thing with the fat lead which clips to a place on the CRT. The
fat lead is the Anode lead-- a High Voltage charge on this lead is
likely. A High Voltage charge at the connection point on the CRT is
likely.  A High Voltage charge anywhere around the connection point on
the CRT surface is likely-- it is not unusual for the CRT surface in
this area to be conductive.


     The pic below shows a typical way the Anode is clipped to a CRT.


 
      ---     ---  <-- clip inside conductive recess in CRT
  =====  \   /  =========== back of CRT (may be conductive!)
          \ /  <-- metal clip usually covered by a rubber cup.
           |                     
          [|]
          [|]  insulated Anode lead going to HV module
          [|]


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 of good quality. You can, probably, _reduce_ the
shock hazard by discharging the High Voltage at the anode. You can not,
really, expect to eliminate the shock hazard. (See WARNING below.)

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.

WARNING: After "discharging", do _not_ assume that no High Voltage is
present. Almost certainly, some High Voltage remains or may reappear
over time.


     After "discharging" (you hope) the Anode, you can use _insulated_
narrow long-nosed pliers to grip the Anode clip beneath the cup and
twist it slightly. If necessary, you can hold the CRT steady with your
other hand at the plastic shell which normally surrounds the front of
the CRT. (Do NOT hold any metal part of the monitor or touch any part of
the CRT itself with your other hand.)


     As was mentioned earlier, another possibility is some loose
component. Finding and fixing a loose capacitor, resistor, switch, etc.
is a job for someone with repair experience. If you locate an obviously
loose component and wish to resolder the connection, remember to avoid
touching more than one conductive point at a time when doing the
soldering.

     Again, if you are new to monitor repairs and have a friend with
TV/monitor repair experience, it is a good idea to ask him/her to do the
inside monitor stuff.
     


Rubywand