monitor SILICON GRAPHICS - Adaptation for PC

Return to the synopsis        version française


I want to thanks Sylvain Grosjean, electronic teacher for all the time and the assistance that he brought to me, and Julien Leduc for the technical assistance brought.

I thank also Adam Kropelin ( ) who have give me the right to re-use his photograpy of the back of a GDM-20D11.


It is sometimes very interesting to re-use old monitors of workstation for our PC computers, but it could be difficult to adapt these monitors to use them on PC because their operating mode is often different. I present here the adaptation i had made and which function for my monitor SONY GDM 20D11 to use it on my PC. Of course, you can reproduce this solution at your own risks, I decline any responsibility for the damages that that could cause the use of the informations you can find in this page.



A part of the monitor, in the switching power supply, is connected to 220 V (or 120 V for country in 120 V)
A part of the monitor is under very high voltage (up to 25 000 V)

Even disconnected, some capacitor can remain charged under high tension
(300 V rather classically). Attention with the discharges.

Consult the security page of the site

Presentation of the issue

The monitor SONY GDM20D11 is a fixed frequencies monitor whose frequencies of synchronization are higher than the frequencies used for  VGA   (31,5 Khz in horizontal frequency, 60 vertical Hz) we can use it under X11 or windows with the right resolution and the right frequencies. However VGA mode is used to start the PC (bios tests) and the operating system (text mode starting for linux, starting windows  for windows). It is also used for the "safe mode" of windows. This monitor synchronize from 48 to 82 Khz horizontally and near 70 Hz vertically. You can use it between 1024x768 70 Hz to 1280x1024 70 Hz (it could also be used in 1600x1200, but some pixels are mixed).

According to the monitor has the following characteristics:

surface display
freq hrz (Khz)
freq green (Hz)
physical resolution max *
Sony (Sgi)
GDM 20D11
* this does not prevent from displaying higher resolutions (it is most surely the case on your monitor in this moment)

The tube is a " black trinitron ", which means that this monitor does not display a distorsion along the vertical axis (the surface of the monitor is cylindrical and not " spherical " as on the majority of the monitors).

The second problem (and it is not the least), for a user of PC, is that this monitor uses only three input signals: a red, a blue, and a green signal, the green signal containing the signals of synchronization. Even if the connector is a 13W3 (presented further) containing 3 connectors for the colors and 10 pins annex for the others informations, in fact, only the three colours connectors are connected to another thing than the ground or nothing.

Connector HD-15 (side PC)

pin VGA - VESA (principal functions, communication for the nondetailed PNP)
1 RED 
4 BIT ID or reserved
5 not connected
6 red ground
7 green ground
8 blue ground
9 no pin or + 5 V (generally the PC provides +5 V on this pin which can be used to supply power to an external circuitry such as a logical gate used to combine H sync signal and Vsync signal). 
10 ground
11 BID ID 0
12 BIT ID or SDA: DDC serial line data (for PNP  monitors)
13 horizontal synchronization (on certain graphics boards composite synchronisation) 
14 vertical synchronization
15 not connected or SCL: DDC clock line (for PNP monitors)

Connector 13W3 (monitor side)

For the monitor which interests us the pin A1 (center) is connected to the red, the pin A2 with the vert+sync, the pin A3 with blue. Pins 2 to 5 are, in the monitor, " in the air ", the others are connected to the mass.

For other monitors, following interfacings are possible (source: )
Note: the connectors A1, A2 and A3 are armoured and the shielding is always connected to the analog mass.

stitch SGI SUN NeXT IBM Power PC Intergraph GDM20D11
(of visu)
A1 red red red red red Red
A2 green green blue blue green Green
A3 blue blue green green blue Blue
1 id bit 3 NC + 12 V id bit 2 NC GND
2 id bit 0 NC power switch cont id bit 3 NC NC
3 composite sync sense 2  monitor clock auto test monitor sensing 2 NC
4 horizontal drive sense GND monitor out DGND NC NC
5 vertical drive composite sync monitor in Hsync composite sync NC
6 id bit 2 NC - 12 V id bit 0 NC GND
7 id bit 1 NC monitor type id bit 1 NC GND
8 DGND sense 1 GND NC monitor sensing 1 GND
9 DGND sense 0 GND Vsync NC GND
10 sync 2 (obsolete) composite sync GND GND DGND composite sync GND GND


Solutions which not require a modification of the monitor (to be avoided only use to test if monitor is good)

You can find some solutions, using resistors and/or of logical gates. Refer to the " sync one green FAQ " on
These solutions consist in generating a sync on green signal as clean as possible, which is then transmitted to the monitor. Resistor based solutions are not particularly " clean ", Logical gates based solutions and transisor or FET solutions are complicated electronics, requires an external supply voltage and can be dangerous for the monitor in some cases.

Solution for all graphic cards which accept to generate 1024x768 70 Hz minimum

A solution can be used to generate "sync on green" from Hsync,  Vsync and Green signal, by adding all these signals in one, using resistors. This solution works with some problems : If the resistors are too high, the sync signals are not high enough and the monitor doesn't synchronize. If the resistor are too low, the green signal is disturbed and the display is a bad quality one.

This solution can be used to test if the monitor is working correctly, no more.

The value of R is to be determined. Start with resistors near 10 K Ohm, and decrease slowly. The good value is depending on the graphic card. A 100 Ohm value works perfectly with GDM-20D10, but connected to the pin 5, not to the A2 one.

Note: I had tested this solution, it is not the best.  it involves a strong attenuation of the green signal, and the image is not correct any more in term of colors (that depends on your graphics board, but in all the cases it is not very good.) i propose only to use it in order to test the monitor. 

Opening the monitor

The schematic of the solution i had used is presented on pictures re-used frome the Adam Kropelin website. Adam Kropelin had done a good modification to GDM-20D11 to make it works on SUN Worstations. On his website you will find the good methodology to open the monitor properly

the URL est this one :

on the back of this protection is the pcb to be modified.

pcb to be modified

The good cable for the proposed solution

 All the modifications i'm going to propose to you is based on this cable. the red signal (pin one) on HD-15 is connected to red (A1), the green to green (pin 2 to pin A2), the blue is connected to blue (pin 3 to pin A3), all the ground to ground (5,6,7,8,10 to A1 ground, A2 ground, A3 ground),...) the hsync signal (pin 13) to the pin 5 and the vsync signal (pin 14) to the pin 4. 

The first solution, works if you can set the synchro signals to negative on the drivers of your graphic card

This is a good solution i have found later than the other, but which permise to have a very good display and to use the monitor on a PC or on a SGI workstation It is based on the analysis of the electronic engineering, and on the results of older try.

Sun has done the circuitry like that (see the picture next) : The red signal is reported to another electronic card. The blue signal is reported to another electronic card. The green signal is also reported to another electronic card, but is put on the enter of an electronic filter made with two resistor and a capacitor which make what whe called in french a "passe haut". It's a filter which let the high frequencies goes and which stop the low frequencies and the continuous signals.

Existing electronics, before modifications. On the picture next you can see the location of the various components.


I have tried before to add to green signal the Hsync Signal and the Vsync signal through 100 Ohm resistor. This have for consequencies to perturb the green signal.

The idea is, here, to reconstituate the filter with the other passive components than the one which are on the PCB. Using this solution, the two perturbating signal are now linked to the green signal with a very high impedance according to 100 Ohm one.

The schematics is this one : R is linked to pin 1 of  HD15, V is linked to pin 2 of HD-15, B is linked to pin 3 of HD-15, Hsync is linked to pin 13 of HD-15, Vsync  is linked to pin 14 of HD-15 and all signal are corerctly grounded (ground can be found on pin 6,7,8 and on pin 10 of  HD 15.

In order to use the same cable as presented before (you have to do it yourself), the modifications are the one presented on the picture next.

The cable you have to do is this one

What you can also do is to buy a HD-15 to 13W3 adaptor, to test it to see where are connected the HD-15 pin 13 and 14, and to sold the 2,2 K resistor to the correct pin of the 13W3 on the PCB, after having disconnected it from the ground if necessary. (it's what i have done).

Now, plug the monitor and do the correct settings. (you have to do this with a good multisync PC monitor in order to display something even if it's a bad one settings).

because these monitors are not PC compatible, you cannot display the bios test and the boot of your favorite OS. So it's necessary to have at least a 14' monitor which can display VGA mode to do the settings (in "safe mode" of windows or in console mode of linux).

Some graphic cards are designed to display all mode on fixed frequencies monitors, but this graphic cards are so expensive that it will be better to buy a monitor ! The interest of these is that you don't have to modify anything in the monitor. These graphic cards generate a correct "sync on green".  If you wan't too, see .'s another manufacturer i have found, but i have forgotten the link and the name. The price seems to be quite equal to Si87.

Even if you put a high resolution on windows or linux, there's no chance that it can works correctly on the first try. In fact, it's necessary to adjust two or three things:

Because a lot of graphic cards does not have this sort of settings you will have to download (and to buy if its works correctly) some soft, especially for windows users (linux one should have more freedom to set the parameters as they wan't too, see X11 manual).

Two softs seems to permise this : powerstrip and univbe. I have tried powerstrip (not the 3rd version but the 2.78 version only), which works correctly but which start at the end of the windows boot. very good for searching good parameters. Then i used only the soft of my graphic card (matrox) as you can see next.

Correct settings

As you can see on the picture next, the settings displayed are correct. But be careful : The settings you can see next, are used on a PII 333 operating under windows 2000 professionnal at my works. It replace an old 17'' of bad quality and is very confortable to use CAD soft such as catia V5. The videocard is an MATROX AGP G200.

a modification for all graphic cards

The whole explanations are given on the french page. my english is too poor to repeat all these explanation here. i'm using a XOR gate (74HCT86) (the symbol is a rectangle with "=1" written inside on the french schematics) and pair of resistance and capacitor in order to transform all sort of synchros (positive or negative) in negative one. The principle is to generate the mean of the signals by using filters ("passe bas" in french), and to make a XOR of the signal and it's own mean. The schematic is this one :

what we want to obtain in all casessignaux synchros

what we can have in entrance(four cases possible):     signes

The schematic principe

with R1=R2=10KOhm
with C1=100nF
with C2=10uF
with R3=R4=2,2KOhm and C=100uF like in the first solutions (the difference is the use of a gate.

The PCB is this one :(GIF 300 DPI) typons

The implementation is this one : implantation

The PCB was made with the soft TCI from bruno urbani : (freeware)

Connect the +5V to +5V of the M1 PCB, the GND to the ground, the Hsync to your hsync (where you have putted it) the vsync to the vsync (idem) and the G point (GDM-OUT) to the base of the transistor, at the same place the capacitor is sold in the previous solution.
modif carte


simply set your monitor to 1024x768 or 1280x1024 at 70 or 72 or 75Hz and it will works correctly. Then, use the remote control or your graphic card soft to adjust the display on the monitor.

About the GDM-20D10

They accept a composite sync on the pin 5 of  the 13W3. So there's no problems about disturbing the green signal, so it's sufficient to make a cable with an addition of Hsync and Vsync through 100 Ohm resistor (or more) connected to the pin 5 of 13W3.

a GDM20D10 have four display mode :
1280x1024 81,1 kHz 76 Hz ;
1152x900 71,8 kHz 77 Hz ;
1280x1024 71,7 kHz 67 Hz ;
1152x900 61,8 kHz 66  Hz;

I suppose that the choice between the different mode are made by the type of the synchro (negative-negative, negative-positive, positive-negative, positive-positive) but i don't know
which one is set to which resolution.


For the rest, it's nearly the same monitors than GDM-20D11 and the settings problem is nearly the same (the correct frequencies can be quite different. See the manual sold with the monitor .
you can find two principal pages of this manual here :

the doc of the cxa 1616S can be found here :

a modeline to make a gdm20d11 works correctly in 1600x1200 (thank's to Yann E morin)
Modeline "1600x1200" 162.30  1600 1616 1808 2040  1200 1200 1203 1248 -hsync -vsync

For any informations, you can contact, in french if possible. All question in english should have a reply in a long delay, and in a poor english (see this page to judge).

Don't forget that, if you want to do some modif on your monitor, it's at your own risks, I can't be responsible for the use you can do of this page.