I have an old vf-2 I got cheap with the same problem. They sold it dirt cheap 'for parts" because it would not "power up" and it was not worth their time to diagnose it.
When I hooked it up, I found everything working, except the monitor, which had gone bad. I want to put an LCD on it and went through a lot to figure out how.
First, the old monitors are MGA - the 9 pin is not the DE-9 VGA semi-standard, but rather the original IBM monochrome video (remember the original IBM PC with the green screen monitor?).
Later came color - CGA then EGA. All of these, MGA, CGA and EGA are digital signals, whereas VGA is analog. The sync is compatible with VGA, but the video levels and horizontal refresh aren't. So those are the two problems - signal level and refresh rate.
The signal levels are TTL (about 3-5 volts peak) and VGA is .7 volts p-p although some VGA will take 1 volt p-p. If quality is not a big deal, a simple resistor network will fix the levels.
The refresh rate is the biggest problem. You need a monitor that can sync to the 15 KHz refresh rate of MGA / CGA. Most current monitors only go down to 30 KHz.
15KHz is about the same frequency as NTSC, so these are your options:
1) Buy an old IBM PC era (early 80's) monitor from a used equipment place or flea market.
2) Convert the signal to NTSC and feed it to a monitor that takes NTSC. These are more prevalent than monitors that take VGA at 15 KHz (although during the mid 90's there were some models that did). The circuit to convert to NTSC is more complex, but not too complicated.
3) Get a scan line doubler. Unfortunately, most of these are in the $900 to $3000 range which makes this option a no-go. It is cheaper to convert your system to full HAAS LCD.
4) Convert your system to HAAS LCD by replacing the video board and monitor.
5) I just found this option... Several far east manufacturers have started making converters for older video game consoles to use a VGA monitor. These normally hook to a TV. This, as it turns out, is exactly what is needed. A search on eBay (search for "CGA VGA") turns up several models under $100. You just need to make your own cable for the input, which is trivial.
I am doing option 5 immediately to get the thing going, but will do option 4 eventually.
Go to Wikipedia and look up MGA (actually listed under MDA on Wikipedia) and CGA for the pinouts.
On the DE-9 connector, pins 1,2 are ground, pin 8 is horz sync and pin 9 is vert sync. Intensity is pin 6.
MGA (and HAAS) use pin 7 for monochrome video with pins 3,4,5 unused. CGA uses pins 3,4,5 for RGB with pin 7 unused. Most monitors that take CGA also take MGA and figure out which pins have signal. The eBay adapters also do this.
Good luck.  |