The early ABI Boardmaster 4000 systems were sold without an LCD built in and a Philips CRT MDA monitor was sold separately. Later the LCD became optional and finally it came installed as standard.
These early models without an LCD can be updated to the later firmware so are just as useful as the later models but the video output is a problem. MDA TTL 18khz video is not really used outside of early IBM computers and industrial equipment such as CNC machines.
Since IBM 1550 monitors are quite rare and collectable these days as well as being fairly unreliable tracking down a large CRT from the 80s isn't an ideal solution.
I did some googling for an MDA compatible LCD monitor, there's one on ebay sold for CNC machines which would work but the price is very high. There's also scan converters such as the GBS8218 that would work but still a little more than I was looking to spend.
I then found a forum post and
this page that suggested the BenQ BL702A may work. The monitors listed are obviously not tested for MDA and only tested on Atari / Amiga computers but if they support low, medium and high resolutions there's a chance they might support MDA too.
I decided to pick up a G922HDL which is also a BenQ as there were some very cheap ones on ebay. Unfortunately this one doesn't support MDA and just displays 'out of range'.
A couple of weeks later a 17" BL702A showed up on ebay and I decided to bid as even if it didn't work it's a nice size for testing Amigas and possibly medium resolution arcade pcbs.
The BL702A works pretty well, I had to play with the settings a bit to get it centered and adjust sharpness and phase. There are some rows of pixels that aren't as clear, they look missing in the pictures but it looks better in person. I think the phase needs changing more than the monitor will allow, it is perfectly usable though.
I like it even better in green. :)
Wiring up a vga to boardmaster cable was fairly straight forward, the video pinout is in the manual.
Ground to Ground, Horizontal Sync to Horizontal Sync, Vertical Sync to Vertical Sync and TTL Video to Red, Green or Blue (or all three) through a 470ohm resistor. I recommend green only as then you have the option of green or white.
So there you have it, if you're a CNC, IBM computer or Boardmaster owner that needs a new monitor order yourself a BenQ BL702A. At the time of writing this they're still available and are being sold new for around £80-£100. There's a 19" model (BL912) too that *should* work but this isn't confirmed.
