Sony GDM20D11 Modification to Accept Separate Sync

Modifying Your Sony GDM20D11 Monitor to Accept Separate Sync

Introduction

The Sony GDM20D11 19" monitor, originally sold with the SGI Indy workstation (and perhaps others), is a common find these days in surplus heaps and old equipment give-aways. It is an excellent monitor, sporting a nice vertically-flat Trinitron (tm) tube with 0.25 mm dot pitch. See Reputable Systems for the GDM20D11's specific specs.

Since the GDM20D11 was distributed with SGI workstations, it expects to see the video sync signal combined with the green video signal (so-called sync-on- green). This is how most (all?) older SGI workstations provided their output. Unfortunately, Sun workstations use the more common composite sync signal which places the sync signals on a separate conductor (pin 5 on a 13W3). This difference means a stock GDM20D11 (or any sync-on-green monitor) will not work with a Sun.

The simple modification described below will allow a GDM20D11 to accept a separate composite sync signal on pin 5, thus allowing it to work with Sun workstations. It will continue to accept sync-on-green as well.

Using the monitor with a PC

This modification alone is not enough to make the GDM20D11 compatible with your average PC. However, Laurent Granjon has a very nice description (also available in French) of how to extend this mod to allow PC compatibility. Ivan Leong also has an excellent page showing another way to make the GDM20D11 work with a PC.

Cables

After you make the sync modification, you will be able to use with monitor with both SGI and Sun equipment. However, you must use a slightly different cable for each platform.

When using the monitor with a Sun, be sure to use a Sun 13W3 video cable (one that has pin 5 wired through). The SGI cables I have seen do not have pin 5 wired and therefore won't work with a Sun, even when the monitor has been modified.

To use the monitor with an SGI machine, you must use a cable that does not wire pin 5 through. SGI equipment expects pin 5 to be disconnected and after modifying your monitor that will no longer be true.

Modification Details

Disclaimer: You're on your own on. Making this modification surely voids your warranty, so if you care about such things, you'd better stop here. I've only ever made this modification to one monitor. It works great for me, but I may have the only GDM20D11 on the planet that it works with. Yours may smoke, throw sparks, stink up your house, or cause your spouse to leave you. I take responsibility for none of these things. You may do something like leave the power cable plugged in and grab the flyback with your left hand and a cold water pipe with your right. I don't take responsibility for that, either.

Having said all that, this is a very simple modification to make. It involves soldering in one 10,000 ohm (10 K ohm) resistor on the signal input circuit board. Only a little disassembly is required to expose the board, and the points you need to solder to have plenty of room around them, so even a relatively inexperienced solderer can do the job safely. The input board carries only very low voltages, so you don't need to get near the scary-looking HV stuff.

Click any of the images below for a larger version.

Step 1: Remove Your IndyCam and Disconnect All Cables
You do have an IndyCam, right!? If you forget this step, I know from experience you will have a surprise awaiting you sometime later when the thing falls off the top. Be sure to remove the power and signal cables as well.

Step 2: Remove the Rear Cover
Removing the rear cover is a simple process of taking out four screws as shown in the picture below. Pull the cover straight back to remove it once the screws are out.

Step 3: Remove Metal Shielding
Remove the metal shield which covers the back of the monitor. Two screws have to come out. One is located above the shield and one is below it (between the shield and the 13W3 connector). Once the screws are out, lift the shield slightly and pull it off.

Step 4: Remove the Input Signal PCB
Remove the four screws holding the input signal PCB and then turn it around so the back of it is facing you. It will still be connected via a number of wires, so don't pull too hard.

Step 5: Solder In the Resistor
The images below show before and after shots of the modification. A 10,000 ohm (10 K ohm) resistor must be soldered to the points shown. One end connects to pin 5 of the 13W3 connector. The other end connects to the monitor's sync input circuit. I suggest that you add a small amount of solder to both points before you solder the resistor. This will allow you to hold the resistor with one hand and the iron with the other and not have to worry about sprouting a third hand to hold the solder. As always, be careful to apply only as much heat as is needed to connect the resistor so you do not damage the PCB or nearby components. I suggest holding the resistor with a pair of needle-nose pliers since the leads will get hot. Also, be sure the bare resistor leads do not contact any pads on the PCB other than the ones you're soldering to. You don't want to short out any other signals.

Step 6: Reassemble
Reverse steps 1 through 4 to reassemble the monitor. If you want, you can mount the input signal PCB and test the monitor immediately before you reassemble the whole thing.

Feel free to send questions, comments, and reports of success or failure to me at akropel1@rochester.rr.com.
Note: I have no experience connecting this monitor to a PC, so if you write to ask about that you will probably be disappointed with my answer...