Sun Monitors on PCs 

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I've recently received a few emailed requests for the following information. I've replied to all of them but one ― I inadvertently deleted that message before even reading it. If you're reading this, please accept my apologies. I'm setting up this page to answer the recent demand.

I got the following information the same way everyone else did: research on the web. Two pages helped me particularly: Hans Leibbrandt's page on connecting Sun monitors to PCs; and this page, about hacking the GDM-17 series.

DISCLAIMER: If you fry your monitor, graphics card, or computer, it's not my fault. For all you know, I'm a luser with a weird sense of humour and I'm winding you up, trying to see how many monitors I can kill with a daft web page.

Why?

There's a fair deal of demand for this sort of thing these days. The monitors used on the older, ‘golden age’ Sun workstations are rock-solid, Sony OEM devices. They're big, aesthetically pleasing and can deal with high refresh rates at high resolutions. Large companies and universities are chucking them out like there's no tomorrow, because many won't (easily) work with the new UltraSPARC machines (they wear SVGA framebuffers and SVGA monitors). It's tempting and feasible to salvage these devices for use with modern machines, be they SPARCs or PCs.

I've personally dealt with two monitors of different generations:

• The Sun 20-inch Premium Colour Monitor. This is a beautiful device from 1994-1995. It's really an OEM version of the Sony GDM-20D10, and you'll see it referred by that name rather than its (numerous) Sun part numbers.
• The Sun 17-inch Premium Colour Monitor. This is a somewhat more recent device, an OEM version of the Sony GDM-17E20. Not as pretty and SPARC-themed as the GDM-20 family, but it has a very crisp picture and a few other characteristics that make it a very worthwhile monitor.

I've also accumulated enough knowledge about the GDM-1962 to bluff my way through (or around) an explanation.

In order to get these monitors to work on a PC, we need to check these things:

1. Mechanical compatibility, i.e. the plug and socket stuff.
2. Signal compatibility: separate sync, composite sync, sync-on-green, the kitchen sync.
3. Making it Sync: all you ever wanted to know about the arcane art of pixel pushing.

 

1. How to Connect it Physically

The first thing new owners of these monitors seem to say is: ‘ye gods, what is this plug?’. Well, boys and girls, it's a 13W3, used on SGI and Sun workstations. It obviously won't mate with your SVGA's DB15 socket (duh). You have a few options here.

Buy a 13W3-to-DB15 adaptor.

These can set you back around £15-£20 in .uk! They may cost more than your monitor (especially if it was given to you and all you payed was the taxi fare to get it home). If you do get an adaptor, make sure it's the female 13W3 to male DB15, for connecting Sun monitors to PC hosts. The other variety (male 13W3 to female DB15) is also common, but it's meant to connect PC monitors to Sun hosts. Not particularly useful in our case. There are many sources for these (auction sites being a good one). Sun even has its own adaptor cable (doubtless to allow the old, quality monitors to be used with new, crappy workstations). The part number is 530-2357.

Add a cable to the monitor

If you're handy with a soldering iron and an X-acto knife, you can add another cable. You can do this either inside the monitor, so it has two captive cables (one for the Sun, one for the SVGA); or you can make a y-cable, splicing the new cable onto the old one.

House the connection in a small metal box. This avoids interference at the cable joins (believe me, at frequencies these monitors operate, you'll need this). Make sure the SVGA cable you use is high quality, with individually shielded coaxial RGB cables and an overall shielding. If you're cannibalising a SVGA extension cable, buy the thick, less flexible kind ― it probably has individually shielded RGB cables.

Hack the cable (destructive)

Both the GDM-20 and GDM-17 have captive signal cables, so you can't change them. But you can chop off the 13W3 plug and solder a DB15 (SVGA) plug in its place.

Obviously, once this is done, it's no longer possible to use the monitor on a Sun machine.

Hack the cable (non-destructive)

There's a simple way to hack the cable that still allows you to connect the monitor to a PC.

Chop of the 13W3 plug, leaving around 15 cm (around 6 inches) of cable on it. Solder a male DB15 on the cable leaving the monitor; solder a female DB15 on the cable dangling from the severed 13W3 plug (look at the proper wiring here). Your monitor is now equipped with a 13W3 plug and can be connected to an SVGA card, and you have a custom-made 13W3 to DB15 adaptor to allow it to be connected to a Sun workstation too.

Buy a KVM switch box

There are KVM (Keyboard, Video, Mouse) switches around that can mix and match Sun and PC monitors, and Sun and PC workstations. The good quality ones that can handle Sun monitor frequencies tend to be expensive, and the cheap kinds will probably introduce horrible noise to your images. I wouldn't do it, but your mileage may vary!  

2. Why it Won't Switch On/Show a Picture

So, you managed to connect the monitor to your SVGA card, you turned on the machine, and nothing happened? The monitor turned on, degaussed itself, then switched itself back off?

First, if you're using a hacked-together adaptor, make sure you've wired everything properly.

Now comes the interesting bit. Sun monitors use composite sync. SVGAs use separate sync. The horizontal synchronisation signal lets the monitor know when a single raster (scan line) has been completed, and the electron ray returns to the left side of the screen. Vertical synchronisation lets the monitor know when the bottom of the display has been reached, at which point the electron ray returns to the top of the screen (flyback, vertical refresh).

Different manufacturers use different ways of conveying these signals to the monitor. Separate sync provides the two signals on separate cables. The SVGA does this (requiring five signals to go to the monitor: red, green, blue, horizontal sync and vertical sync).

Composite sync combines the two signals and provides them on a single cable (four signals are required by the monitor).

Sync-on-green combines synchronisation with the Green component (three signals are needed).

So: we need to convert separate sync to composite sync and feed it to the monitor. We're in luck: this is much simpler than other sync signal conversions!

The refresh signals from the VGA are at TTL levels. HSync is normally at logical one (+5V), with pulses dropping to logical zero (0V). Vsync is at logical zero with pulses going up. The Sun needs a composite sync signal that's normally at round +3V;horizontal sync pulses drop down to 0V and vertical sync pulses rise up to +5V. This allows us to combine the TTL signals from the SVGA into a nice and friendly composite sync.

I've seen quite a few ways of dealing with this.

• You're lucky or clever, and your 13W3-to-DB15 adaptor already combines the two sync signals. You lucky bastard. You lucky, lucky bastard. Et cetera.
• You're lucky or clever, and you have an SVGA that will produce composite sync. ATI cards do this: my Radeon 7500 does it, in Windows and X. I believe some older Matrox cards could also do it. You'll need software support to do it, though, and you won't get a picture until the card is told to enable composite sync. So, you probably won't be able to see your BIOS display or VGA text modes.
• Just connect the two sync signals together (an example is here).
• Connect the two signals using a 330Ω resistor.
• Connect the two signals using a small capacitor (an example and explanation).
• Connect the two signals using active high-speed logic (an XOR gate, I believe). I don't much like this idea because it needs external power and the quality depends very much on the propagation delay of the gate. Passive components seem to work much better. And they're much more economical too!

There are also a few different places to add this modification, depending on your tastes, needs and expertise with the soldering iron.

• Modify your SVGA board itself. I've seen an SVGA with a 330Ω resistor soldered across the horizontal/vertical sync pads. I won't vouch for this approach. Framebuffers are delicate devices and you generally don't want to impair them by modifying them on-board. I can't guarantee the card will work with ordinary SVGA monitors after the modification.
• Modify the adaptor (if you have one). This is a nice idea, but not really feasible as most adaptors are made of moulded plastic and can't be tampered with.
• Modify the monitor cable or plug. Much easier and safer. I've done this. For good measure, I've added a little switch that disconnects the capacitor. This makes my GDM-20D10 work with Suns too. There's virtually no loss in signal quality, but I've been pretty pedantic in implementing the mod.
• Modify the monitor itself. I have done this (albeit with a resistor rather than a plain connection). It works well, and does not compromise Sun compatibility either! If you have a GDM-17E20, I thoroughly recommend it. You'll need a bit of patience, as these Sony monitors have lots of screws and metal places you need to remove. But it's worth it.

  Before you modify your monitor, however, test it without the modification. I have reasons to believe the GDM-17E20 will understand separate sync on its own (which means its only incompatibility is mechanical ― the shape of the connector). If this is true, this is an ideal (if bulky) monitor for the PC user.

 

3. Making it Sync

So, everything is set. The monitor powers up, degausses itself, then goes back to sleep again. Perhaps you're not feeding it the right frequencies!

Here's the deal.

GDM-20D10 (and friends)

This is a multisync monitor, but not one designed for the PC. It can synchronise to a wide range of frequencies (approximately 40-82 kHz horizontal, 50-180 Hz vertical), but they're higher than you might like. Here are its sync specs (and a few modes), in XFree86 format:

Section "Monitor"
	Identifier	"Sony GDM-20D10"
	HorizSync	40-82
	VertRefresh	50-180
	Option		"DPMS"

        Modeline "gdm_1600x1200" 162 1600 1664 1856 2160 1200 1201 1204 1250 +HSync +VSync
        Modeline "gdm_1280x1024" 80 1280 1312 1456 1712 1024 1027 1030 1064
        ModeLine "gdm_1152x864" 105 1152 1192 1352 1440 864 865 875 895
        Modeline "gdm_1024x768" 110 1024 1056 1184 1360 768 770 774 805
        Modeline "gdm_800x600" 65 800 816 880 1048 600 600 603 631 +hsync +vsync
        Modeline "gdm_640x480" 50 640 648 696 832 480 481 484 509 +hsync +vsync
        Modeline "gdm_720x600" 55 720 728 776 912 600 600 603 631 +hsync +vsync
        Modeline "gdm_720x540" 55 720 728 776 912 540 541 544 569 +hsync +vsync
EndSection

The bad news: this monitor won't sync to most standard VGA modes and below. For instance, it's not able to display the default BIOS modes for 320x200 graphics, or 80x25 text. Under Linux or Windows you can bypass this problem. I use a 1280x1024 pixel, 160x64 character graphical console in Linux. Under Windows, you can tweak the registry or use your video card's software. There's nothing you can do for the BIOS modes (short of hacking the BIOS image itself, something I don't really recommend).

My solution is relatively simple: I use a second monitor. I already have a lovely, crisp Compaq 151FS next to the GDM-20D10. It's Hecate the server's monitor. I've modified a simple monitor switch so that it has two positions of operation: normal (both machines display on their monitors) and 'take-over' in which Vennëa's framebuffer is displayed on Hecate's monitor, and Hecate's framebuffer is not displayed anywhere.

If you do something like this, make sure the switch box is metal and rewire it with high quality, shielded cable. The cables used normally are hardly suitable for TTL use! I used pieces of an old, high quality monitor cable with individually shielded signal cables.

GDM-17E20 (and friends)

You're in luck! This is a multisync monitor that'll work on the PC's full range of sync frequencies. I have reason to believe you won't even have to sort out the composite sync issue, as the monitor probably understands separate sync on its own. I don't have much to give you here and there's no need for special instructions. Try different modes and find the one you prefer.

GDM-1962

Oooh, here's a problem case. This is not a multisync monitor. It's a fixed frequency device. As such, it won't display anything unless it's at its own frequency. It might even fry if you feed it the wrong frequencies! You have been warned.

The GDM-1962 can sync at 61.8 kHz/66 Hz and 71.7 kHz/76 Hz (horizontal/vertical). It was made to be used at 1152x900 and 1280x1024. You'll probably have trouble getting SVGAs to conform to this sort of specification with that much accuracy (most cards I know have a 1 kHz resolution in their programmable clocks).

Your best bet with this monitor is to find a special PC graphics card that can drive fixed frequency monitors. I have seen a couple of these beasties (one was a 1991 Miro implementation of the TIGA standard and was actually made for the GDM-1962; the other is a fancy, 2D/3D AGP accelerator board that was made to drive fixed frequency monitors. It came with my GDM-20D10 and it can display the standard VGA text modes on fixed frequency monitors, too! It just uses huge margins (effectively, the 720x400 resolution of the VGA's text mode is rendered as a centred, small window on a 1280x1024 frame!).