While the Apple IIgs could connect to a composite display, Apple released a high-quality color RGB monitor specifically designed for the IIgs. This monitor was called the Apple Color RGB Monitor, A2M6014. It was the only color monitor Apple ever released which could accept full analog RGB video signals at the standard 240p/480i resolution (using a 15.7KHz horizontal line frequency). I have recently acquired a full Apple IIgs setup, and while the IIgs needs some repair to its mainboard the monitor works. Even though this monitor has a connector only used by Apple, with a converter it is possible to use it with a variety of game consoles. In this short blog article I will detail how I got it working with my Analogue consoles and MiSTer.
The Apple Color RGB Monitor is a 12"/11.5" viewable display and has a DA-15 female port on the back for video input and comes with a DA-15 male-to-male cable for connecting to a IIgs.
The pinouts of the analog video connector as VGA compatible with one exception, the sync. Apple monitors use composite sync, VGA monitors expect separate sync (H + V). The Apple sync level is TTL sync. Apple continued to use this connector with the Macintosh II and later machines, which only supports high refresh rate (31.5KHz) VGA-style displays. These connectors also support separate sync and even sync over green, but as this page says, "it's complicated."
But back to our humble 15.7KHz Apple analog video display. Most classic video game consoles operate inherently in the RGB domain and most post-crash systems can output RGB (although some require a little help). Systems which support RGB natively or with a simple mod include the Sega Mark III/Master System, PC Engine/TurboGrafx-16, Sega Mega Drive/Genesis, Super Famicom/Super Nintendo, Neo Geo MVS/AES, Atari Jaguar, Sony PlayStation, Nintendo 64, Sega Dreamcast, GameCube (PAL), PlayStation 2, Wii (PAL). Most either output RGB using composite sync, sync on luma or sync via composite video, the latter two may require the extra components to be filtered out to work with this Apple display. This display may not work properly with consoles which output 75-ohm terminated sync. Some consoles like the SNES and Genesis output TTL sync, so a simple cable will work for these consoles.
The Analogue consoles, the Nt Mini (& Mini Noir), Super Nt and Mega Sg all support analog video output, the Nt Mini has built-in analog video while the Super Nt and Mega Sg require the connection of the Analogue DAC. Analogue uses a "VGA connector" for its video output and the consoles can repurpose the pins for RGB Video, Component Video and S-Video/Composite Video with appropriate adapters. For my Sony PVM-1342, I simply use the 6' Monoprice BNC to VGA adapter (VGA male to 5-connector BNC male version) This monitor and cable setup also work with a MiSTer via the Analog I/O board and the Analogizer adapter attached to an Analogue Pocket.
Analogue consoles auto-detect which adapter is connected via certain pins in the VGA connector being grounded. For a RGB cable, pins 11 or 15 must be grounded. Component requires none of these pins to be grounded and Composite Video requires pin 4 to be grounded. Usually the appropriate pin is connected to pin 5 or 10, which are the canonical VGA signal grounding pins.
MiSTer allows you to set the cable output to RGB/Component (vga_mode) and sync type (composite_sync) in the MiSTer.ini file. The Analogizer allows you to set the output via Video Option choices for most cores. Choose the RGBS. option RGB requires the Sync-on-Green switch to be set to Off on the adapter. Neither require pins to be grounded on the cables connected to them.
In order to connect an HD-15 connector to a DA-15 Apple video connector, you need an adapter like this one. These things are simple passive adapters which redirect or ground pins. This has 10 dipswitches to adapt various monitors but for this one you only need to flip Switch 5 into the On position. I used a 1' StarTech VGA to BNC adapter (VGA male to 5 connector BNC female version) to adapt the Monoprice BNC connectors back to a VGA connector. Only the gray sync cable needs to be connected, the black can be left dangling. I tried using a straight-through VGA to VGA male-to-male cable but it would not with Analogue DAC possibly because it did not have the detection pin grounded. MiSTer will work with a straight VGA to VGA cable because of its ini configurability.
Once I had all the cables and adapters connected and the DIP switch set properly, I observed the resulting output was a bit dim. Keep in mind that this tube is close to 40 years old. The system which it came with was used for business so the monitor might have seen daily use for years. Even at max contrast and high brightness settings the picture looked dimmer than my PVM. I turned off the 700mV RGB level option in the DAC video settings and saw excellently bright (for a CRT) and picture with vivid colors and excellent contrast. MiSTer does not have this option and I was able to get a bright enough picture with its RGB output but the most vivid picture comes with the Analogue consoles when the monitor is driven at 1V. This does not overdrive the monitor, it is designed to accept 0.5 - 1.5V according to the manual.
The monitor has three control knobs on the back, vertical hold, vertical size and horizontal position. The monitor can accept a PAL 50Hz signal but you will need to adjust the vertical size and possibly the vertical hold when switching between NTSC 60Hz and PAL 50Hz. For Analogue consoles the "default' horizontal position will show some of the left side of the images cropped by the overscan. You can use the horizontal position adjust to shift the image to the right but I found that any kind of resolution mode change will cause the picture to lose sync, show a garbled image and produce a high pitched whine if the picture is set too far to the right. The knob will need to be adjusted back to the left to resolve the issue. Even with the cropping nothing essential is lost, many consumer TV sets back then cropped a lot more.
Some of the MiSTer arcade cores have horizontal and vertical offset settings which can shift the image and help some of the graphic elements escape from the overscan. These do not trigger loss of sync with the Apple monitor in my experience. While you can put the monitor on its side for 'tate mode games like Pac-Man or Arkanoid and not block ventilation you may lose color on one side of the tube.
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