Introduction
I bought a refurbished 19 inches monitor. It is a Formac ProNitron, but I don’t know the model. Inside, it uses a Sony GDM-1950.
Problems are: the monitor isn’t multiscan, and the connectors are BNC types.The solution is to make a new cable, with sense connected in the right way.
I find that the Sony GDM-1950 can do 1024×768 at 75 Hz. In the Apple video mode, it’s a third party 19 inches. The Sony GDM-1950 was used also in Rasterops 1960, and E-Machine T19 monitors.
Description
Connection with old style connector (DB-15 single density)
The sense on the Apple video plug should be connected like this:
Sense 0 (pin 10) not connected.
Sense 1 (pin 7) connected to sense 2 (pin 4).
Look at Apple technote HW30 for more info on sense modes. You’ll need 5 BNC, and a DB-15 male connector (not a high density one).
Here is the connections :
| DB-15 Mac | Name | Output | |
| 1 | Red Gnd | —— | BNC Red Gnd |
| 2 | Red | —— | BNC Red |
| 3 | /CSYNC | ||
| 4 | sense 2 | —— | sense 1 (DB-15) |
| 5 | Green | —— | BNC Green |
| 6 | Green Gnd | —— | BNC Green Gnd |
| 7 | sense 1 | —— | sense 2 (DB-15) |
| 8 | |||
| 9 | Blue | —— | BNC Blue |
| 10 | sense 0 | ||
| 11 | C&VSYNC Gnd | —— | BNC VSYNC Gnd |
| 12 | /VSYNC | —— | BNC VSYNC |
| 13 | Blue Gnd | —— | BNC Blue Gnd |
| 14 | HSYNC Gnd | —— | BNC HSYNC Gnd |
| 15 | /HSYNC | —— | BNC HSYNC |
Connect with VGA connector
| DB15 VGA | Name | Output | |
| 1 | Red | —— | |
| 2 | Green | —— | |
| 3 | Blue | —— | |
| 4 | ID 2 : nc | ||
| 5 | Gnd | —— | |
| 6 | Red Gnd | —— | |
| 7 | Green Gnd | —— | |
| 8 | Blue Gnd | —— | |
| 9 | nc | ||
| 10 | Gnd | —— | |
| 11 | ID 0 : Gnd | —— | |
| 12 | ID 1 : Gnd (or DDC data) | —— | |
| 13 | Horizontal Synchronization | —— | |
| 14 | Vertical Synchronization | —— | |
| 15 | nc (or DDC Clock) | ||
Modes
| ID 0 | ID 1 | ID 2 | mode |
| nc | nc | nc | no monitor |
| nc | nc | Gnd | monochrome monitor below 1024×768 |
| nc | Gnd | nc | color monitor below 1024×768 |
| Gnd | Gnd | nc | color monitor above 1024×768 |
Use under differents OS
DB15 Macs
The Sony GDM-1950 don’t use inverted synchronization signal. That is why you need to use the sense pins. When there are connected in the good way the /HSYNC and /VSYNC from the Macintosh video, become HSYNC and VSYNC. Under Linux it isn’t done in a good way in the current kernel (2.1.130). You’ll need to change the SYNC mode, in the video mode definitions (number 16 and 17) in the file /drivers/video/macmodes.c, and recompile the kernel.
VGA Macs
Once there is no sense pin (there is, but they are not used), on other monitor needs to be used.
The Mac needs to be started without any monitor connected. This is needed for the mac to think there is a generic monitor connected (new monitor do support DCC protocol, and communicate with the computer).
Then, when the computer has finished its boot process, connect a multisync monitor (by default the resolution is 640×480@67).
Then select the 1024×768@74.9 resolution. Don’t use the 1024×768@75 as synchronisation signal are inverted in the mode.
Keep the computer running, and unplug the multi-sync monitor. Then plug the GDM-1950 monitor.
Set the image size and synchronisation (see below).
Switch off the monitor and reboot.
For start-up the monitor MUST be powered-up 30 seconds after the computer.
This because, at start-up the computer is set to 640×480@67 resolution. It is during the boot process that the resolution is switched to the selected one (1024×768@74.9).
Adjustments
You’ll need also to set the screen ajustments (side left when the monitor is in front of you). Warning : don’t do this if you are not familar with monitors because there is dangerous voltage inside and you need to open the case.
- H-FREQ (horizontal frequency). Because the monitor isn’t multiscan, you’ll need to find the good H-FREQ for him.
- H-PHASE (horizontal phase). Move the begining of the screen horizontally. (time between the H-SYNC pulse and the first pixel of the line)
- H-CENT (horizontal center). Move all the screen horizontally.
- H-SIZE (horizontal size). Change size of the screen horizontally.
- V-SIZE (vertical size). Like H-SIZE but vertically.
- V-CENT (vertical center). Like V-CENT but vertically.
- KEY. Change the trapezoidal of the screen vertically. Needed to have the same width of a line, at the top and at the bottom of the screen.
- KEY BAL (key balance). Change the trapezoidal of the screen vertically. Needed to have 90 degrees angles on the screen.
- PIN AMP (pincushion amplitude). Needed to have the same width for all lines of the screen.
- PIN (pincushion). Needed to not have a vertical curved screen.
There is also some adjusments for the focus (on the right of the monitor). Two kind of adjusments: vertical focus and horizontal focus. For each one the is 12 zones (left, middle left, middle right, right <-> top, middle, bottom). You should start at the middle of the screen, and set horizontal, and vertical in the same zone at the same time.
Troubles
If parts of the screen change of color when you move windows, it’s probably because your monitor is a little older an the power is failling to display a full white line.
If display comes completly dark while setting H-FREQ, it’s because you were too high or too low on that setting an the monitor goes into security. You have to switch off and on the monitor to start again with a better value.