4375M Thompson - MGA Multi-sync monitor with the ST
NOTES:
1) You must invert the Horiz and Vert Sync (use 4069 IC) 2) Use Practical Solutions Monitor switcher 3) Monitor does not have audio, must use external amp and speaker 4) Add 68 ohm resistors in series with RGB from Computer.
PICTURE CLARITY
The DOT Pitch on the Thompson is the same as the original ST Color monitor (.31) and the convergance on this monitor is very good. The only problem I have is that it is a 14 inch monitor and you need to sit back another two feet for the scan lines to look the same (the Atari Monitor is a 12 inch). Or you can reduce the size of the screen with the Vert and Horiz size controls.
Monochrome is good (higher scan rate) but you need to change the vert size to max to get the proper ratio (Horiz/Vert size). You need to add 68 ohm resistors in series with the RGB lines from the computer as Color output has a tad too much drive for this monitor. Monochrome out from the ST needs to drive three lines (R,G,B) and loads down so that its drive is slightly lower. (resistors not needed)
FEATURES
This monitor has superimpose ability, multi-sync ability, switching from TTL to Analog mode with either a switch or line going high-low on the Analog plug. Composite Video, TTL, EGA , VGA, PGA and Analog modes are all supported.
CONCLUSION
This monitor should give you a very useable picture and give you the added benefit of having Mono mode available with the click of a button. Not to mention that the new Computers Atari is coming out with will need a Multi -Sync for those higher resolutions and more colors. By the way, the current price of this monitor is $399.00 mail order.
TECHNICAL NOTES
Thompson brings out a 5v supply on the Analog plug that you can use to power the sync inverter (4069 IC) this line can't power anything more than .25W. I used 1/2 of a printer cable I had lying around...the DB25 male that plugs into the ST for the Analog plug to the Thompson.
Below are the pin assignment for the ST and the Thompson.
Thompson DB 25 Plug Atari Monitor Plug
==============================================================
Pin # Signal description Pin # Signal description
2 Red video .6v +going 7 Red Video 1VPP +going
4 Green video .6 +going 6 Green Video 1VPP +going
14 Blue video .6 +going 10 Blue Video 1VPP +going
16 Horiz sync TTL Pos 9 Horiz Sync TTL Neg
17 Vert sync TTL Pos 12 Vert Sync TTL Neg
21 5 Volt supply 8 12 Volt supply for pullup
1 Ground 13 Ground
3 Ground 1 Audio output
5 Ground 4 Monochrome Detect
15 Ground 11 Monochrome 1vpp +going
25 Ground
There are many ways that you can connect, using switches relays or solid state switching IC's, these pins together to achieve Mono and Color modes. I'll just give examples for both modes and leave the actual choice of method to you.
************* COLOR *************
Thompson Res 68 ohm Atari
Pin 2--------~~~~-----------------Pin 7
Pin 4--------~~~~-----------------Pin 6
Pin14--------~~~~-----------------Pin 10
4069 IC (Sync Inverter)
|---------|
Pin 9 Atari -|1 14 |--5v Pin 21 Thompson
Pin 16 Thompson-|2 13 |-Gnd
Pin 12 Atari -|3 12 |
Pin 17 Thompson-|4 11 |-Gnd
Gnd -|5 10 |
|6 9 |-Gnd
Gnd -|7 8 |
|_________|
All grounds are carried through. Pin 14 of the 4069 is bypassed to ground with a 4.7 Ufd cap. Unused input pins on logic chips should not be allowed to float. They must be attached to ground or B+.
********** Monochrome **************
Thompson Atari
Pin 2---------------------Pin 11
Pin 4---------------------Pin 11
Pin 14--------------------Pin 11
Pin 4 to Gnd (Mono Switch Line)
Pin 13 Gnd
All grounds carried through....use same Sync circuit. Sync is the same for both Color and Mono mode. Audio is not provided in the Thompson Monitor and you will have to provide an external amp and speaker for the sound.
The most important thing to realize is that monochrome and color lines can not be hooked up at the same time, that's why you need a multi-pole switch like in Monitor master and the new Astra Monitor switch box. You can make your own or buy one from the above companys. The only part that might be hard to get would be the Atari Plug. One source of the Monitor Plug is Practical Solutions 602-884-9612.
There are many possibilities allowed for in design of the Atari Monitor output plug. Pin 3 of that plug is a general purpose Output line that can be used to throw an electronic latch so that no mechanical button is necessary to switch between Mono and Color mode.
Jeff Rigby
Intersect Software Corp.
3951 Sawyer Rd.
Sarasota, Fl. 34233