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Re: Monitors (again)
Vincent Quinn writes ...
>
> It seems I'm cursed with failing GS monitors: I have a Commodore Amiga
> 1084S (replacement for my failing-but-probably-fixable Apple RGB) on my GS.
> Well, the 1084 has now started acting up too. When the monitor is cold, no
> problem. As it begins to warm up the video 'flicks' off, leaving a blank,
> olive-green coloured screen. The first couple of times this happens a
> gentle tap on the side of the monitor casing brings the display back, but
> as the monitor gets warmer the display goes completely (no amount of
> banging will shift the blank screen).
>
....
As you say, the problem seems to be temp-related. Since, at least
at the start, bopping the case helps, the indication is that some
connection is affected by expansion or contraction.
One possibility is a picture tube with a poor electrode connection.
If this is the problem then you may well be cursed.
Something to check early on is that a control is not dirty. When
the screen goes dark and bopping does not help, try diddling each
control. A dirty control can often be fixed with a squirt of Control
Cleaner into the control-- usually, this requires removing the case.
Another possibility is a fractured solder connection of some
component to the main board. On the GS monitor, the loose component is
often the High Voltage module-- the thing with the fat Hi-Voltage anode
lead which attaches to the picture tube.
Locating a fractured connection can be difficult. With luck, when
inspecting the bottom of the monitor circuit board you may notice a
connection that looks grey instead of shiny. If the unit is powered ON,
you may notice that tapping a particular component (with a plastic tool)
restores the display. One approach is to resolder every main board
connection in the High Voltage area.
Any time you open the case of a monitor there are a number of
safety considerations ...
>>
003- What Safety precautions should I take when working
on my 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 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.
===========================
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).
= = = = = = = = = = = = = =
007- How do fix a Flickering, Jumping, display which sometimes
collapses to a line?
If the monitor exhibits major flickering, periodic collapse of the
display to a line, etc., then it may help to know that a common source
of such problems is one or more bad connections where the High Voltage
module is joined to the main circuit board. (This module is the black
thing with a HV lead running to the CRT-- it's near the left, back. The
slotted nub controls in its case set Focus and base Intensity.) Often
these connections look okay because it is hard to see the small
fractures in the solder surrounding the pins.
The cure is to resolder all of the pins coming from the module (on
the under-side of the circuit board). Before doing the soldering, clip
a wire to the metal chassis and touch the other end to each HV module
pin and other points in the area. While soldering, avoid touching
anything conductive on the monitor with anything but the iron and
solder.
<<
Rubywand