Notes on the Troubleshooting and Repair of Computer and Video Monitors


  13.28) Thernal cycling and component life

(From: Bob Myers (myers@fc.hp.com)).

In a CRT monitor, the shortest-lived component BY FAR is the CRT itself,
and it ages (more properly, the cathode is aging) as long as the heater
is on and the tube is under bias.  Most monitors don't get around to turning
the heater down or off until they enter the DPMS "suspend" or "off" modes.
(And no, screen-savers do NOT help here - the tube is still on and the
cathode is aging.)

Other factors - simply having the circuits hot and powered up in general
means that they're aging.  Clearly, they're NOT aging when they're off.
This needs to be balanced against the thermal-cycling sort of stresses that
you mention which happen during power cycling, and this is why I recommend
shutting off only when you're going to be away for an extended period, such
as overnight.  This is, of course, most important for those components which
have clear heat-related aging, but most do to some extent.  Esp. vulnerable
are things like electrolytic caps, for obvious reasons.

The bottom line is that nothing is ever going to last forever, and trying
to maximize the life of the product is an exercise in making tradeoffs between
various aging/failure mechanisms.

  13.29) Minimum and maximum lifespan of monitors

(From: Bob Myers (myers@fc.hp.com)).

There's no way to set a "minimum" or "maximum" life, as there's quite a
variation from unit to unit.  Some small percentage will fail right out of the
box ("infant mortality") while others will run happily for years.  We normally
speak of a mean, or average, life expectancy, as in "MTBF" ("mean time before
failure").  In a CRT display, the CRT itself is usually the limiting factor in
this, and in THAT specific case we usually speak of "mean time to half-bright"
instead, since it's rare for a CRT to simply die once it's past its early
operating life.  (Excluding such things as mechanical damage and so forth, of
course.)  Mean-time-to-half-bright is just what it says: how long, on average,
can you operate the tube before the brightness drops to half its initial level
for a given set of operating conditions.  (Brightness is ALWAYS slowing
decreasing throughout the tube's life, due to the aging of the cathode and the
phosphor.)  For most tubes with standard cathodes, this will be in the
neighborhood of 10K-15K hours (a little over a year to not quite two years of
continuous operation).

However, what you're experiencing sounds more like a problem in the
high-voltage supply; instability here would result in the sort of symptoms
you're seeing.  It COULD still be related to the tube, but it might be
worthwhile to have this checked out.  Unless, of course, you're ready to buy a
new monitor anyway!

Implications of power saving modes: 

(From: Bob Myers (myers@fc.hp.com)).

Energy Star and similar power-saving certifications generally don't
specify what is done inside the monitor to achieve the power reduction,
just the maximum power dissipation in the "reduced power" state(s).
Still, most designs WILL either reduce the voltage to the filament,
or shut it off completely, depending on the degree of power reduction
needed for a given state.

Thermal stresses would be damaging to the heater and cathode if they
happened significantly more often than the daily power-down (you DO
turn you monitor off for the night, don't you?).  The way to use
these features properly is to NOT set up the system to enter the
more reduced states ("suspend" and "off") until a reasonably long period
has passed with no action.  Use the "standby" state for the first level,
the one you enter after a few minutes (10?) of inactivity, and don't
go beyond that unless the system is inactive long enough to suggest thay
you're going to be away for a while.  But make sure that the system WILL
get to the deepest level of power reduction supported - with the monitor
as close to full off as you can get - when you're going to be away for
a really long while, like overnight.  Turning the monitor off overnight
is the best thing you can do for it.

And no, I don't think these monitors will be that much more difficult
to service, just because they've got power management.  This is usually
a fairly simple addition to the power supply, and doesn't really affect
the complexity of the rest of the unit.  But modern monitors DO tend
to be more complicated anyway - what with digital controls, on-screen
displays, etc. - and so are somewhat more difficult to repair.  It
just doesn't really have much to do with the power-saving bits.

  13.30) Methods to prevent screen burn-in on fixed format monitors

When TVs or monitors are used to display the same pattern day in and day out,
screen burn is likely to result.  This may happen with TVs used extensively
for video games and text display terminals - both situations where the format
of the screen is relatively fixed.  It is not likely with TVs under normal
usage or monitors used with windowing systems (e.g., Win95, X-windows) where
the display changes from time-to-time.

With TVs, your only options are to reduce the brightness or get the kids (you?)
to participate in less mind numbing activities.

For monitors, here are three approaches (they can obviously be used together).

* Blank or dim the screen or use a screen saver when not in use (won't prolong
  CRT life but will reduce possibility of burn-in).

* Only set the brightness and contrast as high as needed for comfortable
  viewing.  Subdued ambient illumination will allow these to be greatly
  reduced (and save energy as well!).

* Randomize the display.  On a text entry terminal, for example, the system
  could be set up to vary the position of the text on the screen by a small
  amount - a random number of pixels horizontally and scan lines vertically
  less than the character size.  This could be done every time it is switched
  on or periodically.  Of course, unless you are the designer or programmer,
  this option probably isn't very viable!

There will always be some degradation of the phosphor even during normal use.
With changing scenes, it will simply result in a long term darkening of the
screen and reduction in maximum brightness (independent of the reduced
mission from the electron guns).  This effect is likely very slight but my
advice is to keep contrast (peak whites) only as high as you need and turn the
brightness down when not using the monitor for a few minutes.  Also see the
section: "Monitor life, energy conservation, and laziness".

  13.31) Monitors, heat, and cooling fans

Electronic equipment in general most often really likes to be kept cool.  Up
to a point, cooler is better.  However, to save a few cents and to avoid
complaints about noise, few monitors come equipped with internal cooling fans
even though these could substantially reduce the internal temperature and may
prolong a trouble free life.

Without a fan, there are still (possibly) simple steps that can be taken to
keep the monitor happy:

* Keep the ambient temperature low.  There is no need for the humans to
  freeze, but if you are uncomfortably warm, so is your monitor.

* Run the monitor at the minimum brightness for your needs.  It is better for
  the monitor and energy conservation use lower ambient illumination and lower
  brightness.  Stress on both the CRT and power supply components is reduced
  and the monitor will run cooler.

* When idle, use a screen blanker (or screen saver that displays a dark
  picture) or take advantage of any power saving modes that may be supported.
  As above, this will reduce stresses on the monitor's components and save
  energy as well.  Of course, turn all the monitors off at night.  See the
  section: "Monitor life, energy conservation, and laziness".

* Make sure the monitor's ventilation holes are not covered or blocked in any
  way.  There should be several inches of clearance on all sides, top, and
  bottom.  Make sure dust doesn't collect - suck it out with a portable vacuum

However, even if you follow these recommendations (or have no control over
some aspects of your monitor's environment and operation), some monitors run
excessively hot.

While I don't know of any controlled studies on this topic, anecdotal evidence
suggests a substantial benefit to forced air cooling for some monitors.

It doesn't take much - even a CPU style 1.5 inch fan will make a noticeable
difference in nearly total silence.

The best place to mount such a fan is probably on the plastic case in the
vicinity of the high power components - power supply or horizontal deflection.
Provide a hole and grill to match the fan.  Orienting it to blow outward is
probably preferred.

Power can be tapped from any convenient source which provides a voltage that
is compatible with the fan.  For example, a 12 VDC fan can run on anything
from 8 V (or somewhat less) to 15 V or so with a corresponding variation in
speed.  The current used by such a fan is generally negligible so it shouldn't
be a problem to find a source with enough excess capacity.

If you really want to be slick, add a circuit to adjust fan speed based on
scan mode (higher scan modes->higher air flow) and/or temperature.

  13.32) Why are prices of video monitors so high compared to similarly sized TVs?

"How come I can buy a 32" Sony Trinitron TV set for $800, but when it comes
 to buying a monitor for my PC, $1400 only gets me a no-name 20" tube?

 Why can't a giant like Sony produce a PC monitor anywhere close in cost to
 an equivalently sized TV set?"

Well, the bottom line is that there isn't much in common between a TV and
computer monitor when one gets down to the details.  The basic principles
of raster scan display apply to both and that is about it!  Monitors would
already be much more expensive if it weren't for the additional fact that
many more TVs are manufactured and sold than monitors - which drives down
their prices still further:

(Some of this from: Mike Stewart (mstewart@whale.st.usm.edu)).

There are several significant factors being overlooked here:

1. Economy of scale. There are still *many* more TV sets being sold than
   computer monitors. Manufacturers order TV chipsets in much larger
   quantities. This drives down the price.

2. Resolution. NTSC TV signals aren't even VGA resolution. Try getting that
   32" Sony Trinitron XBR to give you 1280x1024.  A computer monitor has a
   CRT with a resolution about 2 to 3 times that of a TV of similar size in
   both horizontal and vertical directions.  The beam is also more sharply

3. Refresh rates. NTSC TV signals come at one refresh rate, period. You
   either watch broadcast NTSC at 59.94Hz (interlaced), or you don't watch
   it at all. No nice, clean 72Hz NI display on there. (NOTE: This only
   refers to the 99+% of TV playback equipment that contains no line-
   doubling circuitry. That's fair, as you'll pay a good bit more for a
   non-interlaced, line-doubled NTSC picture than the previous poster
   was complaining about, anyway.)

   Therefore, a auto-scan monitor needs more sophisticated deflection
   and power supply circuitry.  It must run at much higher scan rates
   and this complicates the circuitry as well.

5. Geometry. The precision of a good computer monitor is much greater then
   any TV.  The sides will be parallel and square.  Adjustments are provided
   to eliminate pincushion, keystone, and trapazoid distortions.

6. Stability. The image on a high quality computer monitor is rock solid
   and does not shift position or change size as components warm up, or the
   power line voltage fluctuates, etc.

(From: Bob Myers (myers@fc.hp.com)).

The basic reason for the cost difference between CRTs for computer and TV
is that they are NOT the same product AT ALL.

They do not share ANY major component.  The glass is different (for one thing,
computer tubes are still almost ALL 90 deg. deflection; TV glass is for
110-114 deg. deflection).  The electron guns are different (different
spot size vs. brightness tradeoff).  The shadow masks are different (computer
displays use a much finer dot pitch than the same size TV tube).  Even the
phosphors used are sometimes different.  They are aimed at different markets,
with different requirements, and so are completely separate designs.  They
most often are not even produced on the same production line.

Beyond the CRT, every other major part of the display design is different,
mostly owing to the difference in horizontal rates required (~15.7 kHz for
TV, vs. 30-85 kHz and often MUCH higher for computer displays) and the
need for multifrequency operation in the computer market, combined with the
need to hold to much tighter geometry, convergence, etc. specs at these
higher rates.

In short, the only thing that's the same between a TV set and a computer
monitor is that they're both boxes which make pictures on a glass screen.
Sort of like the Queen Elizabeth II and the Exxon Valdez - yes, they're
both big metal things that float in the ocean, but there's not really all
THAT much in common between the two designs.

  13.33) Why is the resolution of a computer monitor so much better than a TV

Of course, computer displays may run at resolutions of 1280 x 1024 or more.
These are not limited by minor considerations such as channel bandwidth, and
to a lesser extent, cost.  These are separate issues from why a computer
monitor display is so much better even when the number of scan lines is the
same - as with NTSC versus basic VGA (640 x 480).

1. NTSC (525/30) is fundamentally limited by the bandwidth and color encoding
   of the composite video signal.  This is the most significant factor limiting
   any possible display on a TV via the RF/cable/antenna, or composite or NTSC
   (direct A/V) inputs to perhaps half of VGA resolution horizontally.

   PAL (625/25) more closely matches an 800x600 SVGA format but still suffers
   from similar limitations in horizontal resolution.

2. Monitors are designed to provide sharp focus at the expense of brightness.
   TVs don't have great focus but produce brighter display.  This limits both
   horizontal and vertical resolution.

3. Monitor CRTs are designed with much finer dot/line pitch in the shadow/slot
   mask or aperture grill - often better than 2:1 smaller than similar size

4. TVs use interlaced scanning.  Jitter in the vertical also affects perceived
   display quality.

Where a TV/monitor has direct RGB inputs, the limitation is primarily due to
(2) to (4) though they may not have the same high bandwidth circuitry as a
more costly computer monitor.

There are other factors but these are the most important.

  13.34) Combined TV and computer monitor

"This is a 27" VGA monitor which should also be able to be used as an
 NTSC television monitor.  Can anybody comment on it?"

IMO, I think the entire idea of a combined TV/computer monitor is silly
especially when the likely cost premium is taken into account.  Watching
the boob tube will tie up your entire PC.  The optimal size for TV and
computer use is not the same nor are the requirements in terms of scan
rate, resolution, brightness, and sharpness.  Thus, the design will be
inherently more expensive and include more compromises.

So, I will probably be proved wrong by record sales of these things...

  13.35) Problems with designing a combination TV and computer monitor

(From: Bob Myers (myers@fc.hp.com)).

It's possible, and has been done (for instance, Toshiba has one product
and offerings from other companies are available or are on the way).  But
such designs ARE compromises, and won't give the best performance possible
in either application.

There is a fundamental difference between CRTs designed for TV use,
and those used in computer monitors.  It's a brightness/resolution
tradeoff - TV tubes are run about 3X or so the brightness of a typical
computer monitor, but sacrifice the ability to use small spot sizes
and fine dot pitches to do this.  You don't see very many color tubes
running at 100 - 150 fL brightness and still using an 0.28 mm pitch!

  13.36) So, what about truly digital monitors?

"I am really interested in this Digital Revolution (DVD, HD-TV) but what about
 PC monitors? Wouldn't it be great to have a monitor that was also compatible
 with HD-TV? I want to buy a new 17" or 19" but I don't want to invest in CRT
 (analog technology), when will Digital PC Monitors be coming out?"

(From: Bob Myers (myers@fc.hp.com)).

Being compatible with HDTV just means having the right front end to interpret
the signals, just as using NTSC video on a current computer monitor requires a
decoder.  I seriously doubt that we'll see computer displays which are
DIRECTLY capable of handling the HDTV data stream.

Having said that, there is ALREADY a standard for a digital display interface,
which was approved by VESA last year.  The new "Plug & Display" interface
standard supports BOTH digital and analog video outputs on a single standard
connector, enabling monitors with either sort of interface to be easily
supported.  (The host uses ID information from the monitor - already a
standard feature of most CRT displays - to decide which interface to use and
how to configure it for a given monitor.)  There are already products on the
market (a few) or in development using the new interface.

Having said THAT, don't count the CRT monitor out just yet; it'll probably be
with us for some time yet, and there's little reason to use a digital
interface for a CRT-based display (since, under the new standard, you're going
to have BOTH flavors of interface available anyway).  Actually, there is very
little inherent advantage for MOST display technologies in the interface
itself being "digital" (even LCDs are "analog" at the pixel level); the
problems most non-CRT displays have today with "analog" video have to do with
getting a good TIMING reference with which to sample the video, NOT with
whether that video is encoded in digital or analog form.

  13.37) About sync polarity options

Many video cards provide polarity options for each scan mode.  Why?

Probably to be compatible with older monitors.  Most modern monitors are
auto polarity detecting so the settings should not matter.

(Note that some of the digital PC video standard did have specific
sync polarity specifications.)

Some software programs that directly access the video card may even be
changing sync polarity - for apparently no reason - without you being
aware of it.

Your video card determines the maximum video rate you can generate.  The
monitor has to be able to lock to it.  So, if you cannot setup higher than
some specified rate (i.e., the options do not exist in your menu), it is
a function of the video card and drivers.  If you can set it but the
monitor displays garbage or nothing at all, it is a limitation of the
monitor.  The sync polarity rarely makes any difference and if it does,
the effects will be obvious - picture shifted left/right/up/down on screen -
or just won't sync at all.

If you experience problems of this type, experimenting with the sync polarity
may be instructive.

If you do not know what your monitor wants and you have the option, set both
horizontal and vertical sync polarities to be negative as this is nearly
always acceptable (for studio video and VGA/SVGA monitors).

(From: Bob Myers (myers@fc.hp.com)).

This was used in older systems to identify certain display modes, but in
general modern monitors accept either polarity equally well.  Recent display
timing standards have all been written specifying positive-polarity sync
(the sync pulse is at logical "1" rather than "0"), but the use of negative
polarity usually won't do anything except possibly cause the image to be
off-center by the width of the sync pulse.

  13.38) VESA Display Data Channel standard

(From: Bob Myers (myers@fc.hp.com)).

This defined several protocols for digital communications between a
host system and its display.  DDC provides 3 different modes:

DDC1 - A unidirectional (display to host only) serial communications system
         which provides basic display ID and feature support information
         (including supported timings, display size, colorimetry and gamma,
         etc.) to the host.  This uses pin 12 on the 15-pin "VGA" connector as
         a data line.

DDC2B - Adds clock (pin 15) and return (pin 11, I think - I'm at home, and
         don't have the standard with me) to enable at least ID information to 
         be obtained via an I2C interface.  I2C is a bidirectional interface,
         but display control via DDC2B is not defined at this time.

DDC2AB - Full ID and control of the monitor via ACCESS.bus.  As ACCESS.bus is
         basically a command and protocol definition on top of the I2C
         hardware interface, this uses the same lines as DDC2B.

DDC was the first and only definition of the 15-pin D-subminiature
video output connector which VESA has provided.  No further definitions
on this connector will be made, as VESA is instead concentrating on the
new Enhanced Video Connector standard which is due out later this year.
This will define a completely new connector which will include support
for DDC and separate syncs as in the 15-pin D-sub, and will also include
support for audio I/O, video input, and the USB and P1394 serial interfaces.

  13.39) Identifying connections on unknown or cut monitor cables

Obviously, this is best done with a schematic.  However, since such a luxury
may not be possible, how can you go about figuring out where all the wires
go?  Easy answer - very carefully.

For the following, I assume a VGA/SVGA monitor.  You need to identify the
grounds, video signals, H and V sync, and monitor sense lines.  The procedure
is described with respec to a cut cable but if you are trying to identify
an unknown connector type on the monitor, the same comments apply to the
wiring **inside** the monitor.

First identify the grounds.  Use an ohmmeter between each wire and the shell
of the video connector on the monitor.  Resistance will be less than an ohm
for the ground wires.  These will often be colored black.  The shields of
the RGB coaxes will also be connected to ground.

The high bandwidth video signals will always use individual coaxial cables.
These may even be color coded red, green, and blue.  If not, you can determine
which is which later on.  If there are only three such coaxes, they are
the video signals.  If there are four, the extra one may be the H sync.
If there are five, the extra two may be the H and V syncs.  Testing
between these wires and ground with an ohmmeter should measure 75 ohms
for the video terminations.

Display a lively screen on your PC at a resolution you know the monitor
should support (remember, trying to drive a monitor of unknown scan rate
specifications beyond its ratings is like playing Russian Roulette.)
When in doubt, VGA (640x480, 31.4 KHz H, 60 Hz V) should be safe.

Turn up the brightness and contrast on the monitor.  If you are lucky,
even without any sync, there will be a visible raster.  Set it to be just
visible.  If there is none, then it should appear once there is valid sync.

You will need to bring out wires from the video connector on your PC.

Connect the ground of your video card to the ground wires you already
identified on the monitor cable.

Attach a wire in series with a 200-500 ohm resistor to H sync (pin 13)
on the VGA connector.

Momentarily touch the end of this wire to each of the remaining
unidentified wires (including the coaxes if you have 4 or 5 of these and
it is not obvious which are the video signals) on the monitor.  When you 
find the H sync input, the raster should lock in and probably brighten up.
If the monitor was originally whining due to lack of sync, it should quiet

Once you have located H sync, you can remove the resistor and connect the
wire up directly.

Now, attach the video signals.  It is likely that you will now have a
picture but it will be rolling on the screen.  Some monitors, however,
will not unblank until they receive both valid H and V sync.  Use your
resistor with the V sync output of the video card (Pin 14) on the remaining
unidentified wires.  Once you find the V sync input, the display should
lock in solid.

The only remaining unknowns are the monitor sense lines.  For older monitors -
those without the ACCESS.bus interface, you can just wire up the sense lines
to the appropriate levels (Color: ID0 (Pin 11) to ground, ID1 (Pin 12) NC).

See the document "Pinouts for various connectors in Real Life(tm)" for
detailed hookup information".  Replacement VGA connectors are readily

Also see the section: "Replacing the cable on an HP D1182A monitor" for some
hints and helpful 'hassle savers(tm)'.

  13.40) Replacing monitor cables or connectors

Many intermittent or erratic loss of color or loss of sync problems are due
to a bad cable - more specifically, bad connections usually between the male
pins and the wires.  Or, perhaps, one or more pins were accidentally broken
off as a result of the connector being forced in the wrong way around.

Unfortunately, it is all too likely - particularly with newer monitors - that
the shell is molded on and impossible to non-destructively remove to access
the connector for wire repair or pin replacement.

You have several options:

* For name brand monitors, entire replacement cables may be available.  These
  will be pricey ($25 to $50 typical) but are by far the easiest solution.

* The connector itself can be replaced.  Places like MCM Electronics stock
  VGA (HD15) male connectors and pins.  These may be either solder or crimp
  type (both can actually be soldered if you work at it).  It takes a steady
  hand, bright light, and patience to solder the fine wires to the tiny pins.
  A crimp tool is probably not worth the investment for a single repair.

* If you can locate a dead monitor with a good VGA cable still attached, it
  is possible to cut and splice the wires away from the connector.  Use an
  ohmmeter to identify which signal pin connects to which color coded wire
  on each cable and then solder and tape the individual wires.  It won't be
  pretty but should work reasonable well.

  13.41) Replacing the cable on an HP D1182A monitor

(From: Marion D. Kitchens (jkitchen@erols.com)).

By following the procedure in the section: "Identifying connections on unknown or cut monitor cables", I was able to get a D-15 correctly connected on the
ends of an HP D1182A monitor's video cable.  This was a monitor that came to
me with the D-15 missing.  The only remaining unknown is the brown wire but
the monitor seems to work fine without it (however, see below).

 Cable Wire  Internal Pin #   Function   Resistance  D-15 Pin     Notes
 White Coax      5,4          Red Video      75        1,6    shield is 6
 Black Coax      3,1         Green Video     75        2,7    shield is 7
 Red Coax        7,6          Blue Video     75        3,8    shield is 8
 Red              8             Gnd           0         10   red & blue are 
 Blue             9           V. sync        1K         14     twisted pair
 Yellow          10             Gnd           0         10   yellow & clear are
 Clear           11           H. Sync       500         13     twisted pair
 Brown           12             ID0??     Infinite    11??    Works OK w/o

Internal pin numbers refer to a 12 pin, in-line connector inside the monitor.
It is mounted on a circuit board (model XC-1429U printed on board) that is
mounted on the neck of the CTR.  There are 12 pins, but one is blank --
nothing connected.  I have called that one pin # 2 for reference, and the pin
furthermost away I called pin #12.  Double numbers mean the first is connected
to the coax center conductor, and the second is the coax shield.

The double numbered pins under D-15 above mean connect the center conductor of
the coax to the first pin number, and the coax shield to the second pin
number.  All the coax shields should measure zero Ohms to ground, and all the
center conductors should measure about 75 Ohms to ground.  Ground is the outer
shield of the video cable, which is connected to the D-15 connector shell when
doing the wiring job.

Pins 5 & 10 are also listed as ground connections on the D-15 connector.  I
suspect these are for the H. sync & V. sync, but do not know that for a fact.
I connected what I believe to be both ground returns (per the twisted pairs
show above) to pin 10.

The currently unconnected brown wire does have a signal of some sort on it.
At least when trying to find the H. sync and V. sync wires, I got screen
reactions if I connected it to some pins on the D-15 connector.  Since it was
the only "left over" wire when I got H. sync & V. sync correct, I suspect it
to be the ID0 wire.  Yes?  No? Maybe?  Nothing seems to happen when I connect
it to D-15 pin #11.  The monitor SEEMS to be OK without the brown wire
connected to anything (but the color balance is a bit off, green and blue OK,
but red is a pale pink).  An Ohmmeter connected between ground and the brown
wire "acts like" it is charging a capacitor -- resistance starts low and
increases with time to several 10's of Meg.  Is that a clue?

As an aid in finding the correct wiring connections I make a special floppy.
It is a bootable floppy for use in the A: drive.  Boot the computer from that
floppy.  First format a system floppy for the A: drive.  Then copy the
ANSI.SYS file from your C:\DOS\ files to the floppy.  Next write a CONGIF.SYS
file to the floppy, containing one line --- DEVICE=A:\ANSI.SYS Now write three
batch files to the floppy, one for each color.

                        RED.BAT file
                          PROMPT  $p$g$e[41m

                          PROMPT  $p$g$e[42m

                          PROMPT  $p$g$e[44m

In trying to find the H. sync and V. sync, I found it most helpful to use the
following procedure.

1. Connect all of the ground wires, and one of the coax center conductors (any
   one at random) to D-15 pin #1.

2. Boot the computer from the above floppy.  Watch the drive light to
   determine when the boot process is completed.  Hit RETURN twice to get past
   the new time and date that it asks for.

3. Turn on the monitor, and type RED to run the red batch file.

4. Now follow the procedure in the section: "Identifying connections on unknown or cut monitor cables" to find the H & V sync wires.  When you
   have them correct you should see a colored screen (it might be red, green,
   or blue) and two "A:>" prompts on screen.  Make sure the brightness control
   is set for maximum brightness, and that contrast is high.

5. Once you have a readable screen, find the correct coax to produce a red
   screen when connected to D-15 pin #1.  Then type GREEN to run the green
   batch file, and find the correct coax to produce a green screen.  The
   remaining coax is, of course, the blue video.  But verify that anyway by
   typing BLUE to run the blue batch file.

6. Now you should be able to get red, green, and blue screens buy running the
   respective batch files.

To aid in the trial and error process of finding all the correct wiring, I
made a small (3 by 4 inch) PCB with 15 connection points and a large grounding
point, and mounted a D-15 connector on one edge.  The 15 copper traces were
wired to the D-15 connector so that pin numbers 1 through 15 followed a simple
series across one edge of the PCB.  The 15 traces were about 1/4 by 1 inch to
make life easy.  I even soldered 220 Ohm resistors to pin numbers 13 & 14 on
the board to make that easy too.  With this "aid" I used a video extension
cable to bring my working point to the front of the test bench, and had plenty
of working room for all those trial and error connections.  Yes, I do like
'hassle savers(tm)'!

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Written by Samuel M. Goldwasser. | [mailto]. The most recent version is available on the WWW server http://www.repairfaq.org/ [Copyright] [Disclaimer]