I've been restoring/upgrading an 8088 Compaq Portable and I was wondering if it is possible to connect a normal EGA card to the internal CRT? The service guide for the Portable 2 lists the existence of two 8-bit "Enhanced Color Graphics Boards" with the requisite internal connector, but I don't have those.
I determined the pinout of the connector that runs from the MDA/CGA card to the CRT, and it should be relatively straightforward to connect an EGA card with some op-amps and timing adjustments to the CRT. Just to try things out, I swapped in a Zenith Z-449 EGA/VGA card and built a quick board for experimenting with the primary green channel. The CRT did sync at mode 16 (21.85kHz) and drew mostly correct, so I think it's possible. Has anyone here tried this before?
For reference, the pinout of the VDU->CRT connector on my system is:
----------------
| 1 2 3 4 || 5 |
| 6 7 8 9 || 10|
----------------
1 - Red - VSync - Negative Pulse ~150us All Modes, 50Hz MDA, 60Hz CGA
2 - Black - CGA Mode Active? - High in CGA mode, low in MDA mode. My CRT appears to multi-sync and ignore this.
3 - Orange - Analog video data - ~3V max observed
4 - Brown - Hsync - Positive Pulse ~5us All Modes, 15.7kHz CGA, 18.5kHz MDA
5 - Grounding Strap
6,7,8,9 - White - Video Ground
10 - NC
I determined the pinout of the connector that runs from the MDA/CGA card to the CRT, and it should be relatively straightforward to connect an EGA card with some op-amps and timing adjustments to the CRT. Just to try things out, I swapped in a Zenith Z-449 EGA/VGA card and built a quick board for experimenting with the primary green channel. The CRT did sync at mode 16 (21.85kHz) and drew mostly correct, so I think it's possible. Has anyone here tried this before?
For reference, the pinout of the VDU->CRT connector on my system is:
----------------
| 1 2 3 4 || 5 |
| 6 7 8 9 || 10|
----------------
1 - Red - VSync - Negative Pulse ~150us All Modes, 50Hz MDA, 60Hz CGA
2 - Black - CGA Mode Active? - High in CGA mode, low in MDA mode. My CRT appears to multi-sync and ignore this.
3 - Orange - Analog video data - ~3V max observed
4 - Brown - Hsync - Positive Pulse ~5us All Modes, 15.7kHz CGA, 18.5kHz MDA
5 - Grounding Strap
6,7,8,9 - White - Video Ground
10 - NC