lnx64
07-21-2012, 02:51 AM
I have this seriously old computer, an old IBM PC all in one, that used a monochrome CRT with a rather intriguing design. It's a IBM PC XT in an all in one chasis called the model 25.. It's an 8MHz CPU system with 640KB of RAM.. It was my first PC, and sadly, a year ago the flyback blew up (literally).
I only got around to it since last month, looking for flyback donors, and found a possible replacement. It's from a 90's IBM point of sale monitor.
What makes this flyback special? Not much. But the flyback I used, required a few resistors and capacitors to be installed to make it work right, so the flyback is essentially on a daughter card with my mods in place..
The CRT in this monitor was interesting, cause it was dual sync, not fixed frequency or multi sync like most computer monitors.
It could handle basically two modes, 400 lines at 70Hz vertical fresh with 31.77KHz scan rate, and 480 lines a 60Hz vertical fresh, with 31KHz scan rate.
400 line mode was used for 80 column text mode, 40 column mode (pixel doubled in RAM), and 320x200 graphics mode with 64 shades of grey. 480 line mode only had one use, 640x480 graphics mode with basically 1-bit color, on or off (pure monochrome)..
So, I got the CRT up and running, it looked very poor, a lot of smearing of graphics. This is something it never showed before, it looked like a weak CRT. So my friend came over with a sencore and checked it, and it was testing weak.. This is weird, the CRT used to be strong a year ago before the flyback blew up. (Can a flyback cause the CRT to get weak?), but we rejuvenated it, and now it's working FANTASTIC!!
Pics!
1-bit 480 line mode: http://img.photobucket.com/albums/v395/Evilweredragon/IMG_0866.jpg
8-bit 64 shades of grey mode: http://img.photobucket.com/albums/v395/Evilweredragon/IMG_0875.jpg
I'm rather impressed.. I blame radiotvnut, for giving me the courage to start messing with flybacks..
Only one quirk, in 400 line mode, this flyback makes a slight whine, but that's odd considering the horizontal frequency is the same, 31.77KHz, so not sure, if it's the flyback, or something else.. It was designed for 400 line mode, considering it boots up in this mode.
I only got around to it since last month, looking for flyback donors, and found a possible replacement. It's from a 90's IBM point of sale monitor.
What makes this flyback special? Not much. But the flyback I used, required a few resistors and capacitors to be installed to make it work right, so the flyback is essentially on a daughter card with my mods in place..
The CRT in this monitor was interesting, cause it was dual sync, not fixed frequency or multi sync like most computer monitors.
It could handle basically two modes, 400 lines at 70Hz vertical fresh with 31.77KHz scan rate, and 480 lines a 60Hz vertical fresh, with 31KHz scan rate.
400 line mode was used for 80 column text mode, 40 column mode (pixel doubled in RAM), and 320x200 graphics mode with 64 shades of grey. 480 line mode only had one use, 640x480 graphics mode with basically 1-bit color, on or off (pure monochrome)..
So, I got the CRT up and running, it looked very poor, a lot of smearing of graphics. This is something it never showed before, it looked like a weak CRT. So my friend came over with a sencore and checked it, and it was testing weak.. This is weird, the CRT used to be strong a year ago before the flyback blew up. (Can a flyback cause the CRT to get weak?), but we rejuvenated it, and now it's working FANTASTIC!!
Pics!
1-bit 480 line mode: http://img.photobucket.com/albums/v395/Evilweredragon/IMG_0866.jpg
8-bit 64 shades of grey mode: http://img.photobucket.com/albums/v395/Evilweredragon/IMG_0875.jpg
I'm rather impressed.. I blame radiotvnut, for giving me the courage to start messing with flybacks..
Only one quirk, in 400 line mode, this flyback makes a slight whine, but that's odd considering the horizontal frequency is the same, 31.77KHz, so not sure, if it's the flyback, or something else.. It was designed for 400 line mode, considering it boots up in this mode.