How I got a Sony GDM 1660 fixed Frequency Monitor to work on my PC
The Problems
- Normal 'PC' type SVGA monitors are capable of adjusting their vertical and
horizontal scan rates over a wide range of frequencies to cope with different
resolutions. A fixed frequency monitor is designed, like a normal TV, to only work in
a narrow range of horizontal and vertical frequencies.
- 'PC' type SVGA monitors uses separate Horizontal and Vertical synchronization
signals on separate pins on the sub miniature 15 pin 'D' connector. The Sony monitor
uses a scheme called 'Sync on Green' where the horizontal, Vertical and Green signals
are all combined together.
My fixes for both of these problems are described below.
The Hardware
To create a composite sync on green signal from the separate SVGA signals I used
this circuit. There is nothing particularly original about it as I based it on circuits
from sources listed in the bibliography.
Some points to note are:
- The exclusive or gates on the horiz & vertical sync inputs convert the sync pulses
to positive going spikes regardless of if the actual sync signals are positive or
negative going (VGA Monitors use sync polarity to decide what mode they should be
in)
- When sync is low the green signal is 0 Volts(no signal, sync is low)
- When Sync is high the green signal level is the normal video content plus the
an amount dependent on the setting of the potentiometer.
- To adjust the potentiometer, start with it at the 0V side and slowly rotate it
until the monitor falls into sync. Adjusting the level too high may result in color
balance being affected.
- Use SHORT direct connections for the through color leads. We're looking at 100MHz
plus signals here so long dangly leads WILL cause shadows. The best idea would be to
build this onto the actual video card rather than having an adapter dangling on the
back. Mind you I used to use an adaptor on the back, and there seems no real difference to
circuitry built on the board accept the adaptor doesn't keep falling out!
Use these instructions at your own risk. My monitor or video card haven't
blown up yet but if yours does, don't blame me!
The Software
Windows 3.1
If you want to run MS Windows you will need to set up your display driver for a
resolution and refresh rate that gives you the correct scan rates.
I currently use 1280 * 1024 with a refresh rate of 60Hz. This gives me a horizontal
rate of
60 frames per sec * (1024 lines + (a few lines for vert sync, say 30)) = 63Khz
and a vertical rate of
60Hz
which are within the range of operation of the monitor
linux text mode
Here the SVGATextMode package comes into its own. I have my linux text mode set to
100x48 , a marked improvement over 80x25!
Once again the SVGATextMode package can be found as SVGATextMode-1.3.tar.gz
Here are my mode lines.
"My100x48" 65 800 840 934 1032 768 768 769 800 font 8x16
"My80x25" 55 640 704 800 857 400 405 410 427 font 8x16 DoubleScan
X
There is a heap of documentation with X to help with setup. Here are some extracts
from my XF86Config file relevant to the monitor
# SONY Fixed Frequency Monitor #########################################
Section "Monitor"
Identifier "SONY GDM-1660"
VendorName "Sony"
ModelName "GDM-1660"
Bandwidth 110
HorizSync 60-68 # monosync
VertRefresh 57-85 # monosync
# 1024x768 62.03K 77.63Hz
Mode "1024x768#
DotClock 90
HTimings 1024 1148 1268 1451
VTimings 768 772 775 799
EndMode
# Highest Vert Rate 85Hz works 90Hz is too High
# Lowest Vert Rate 57Hz Works 55Hz is too low
# Highest Horiz Rate 68K Works (But display seems to vary in brightness??)
# Lowest Horiz Rate 60K Works 58K Doesn't (Shuts down monitor!)
EndSection
Section "Screen"
Driver "accel"
Device "S3 with Chrontel 8391 Ramdac/clockchip"
Monitor "SONY GDM-1660"
Subsection "Display"
Depth 8
Modes "1024x768"
ViewPort 0 0
Virtual 1024 768
EndSubsection
SubSection "Display"
Depth 16
Weight 565
Modes "1024x768"
ViewPort 0 0
Virtual 1024 768
EndSubsection
EndSection
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