• Please review our updated Terms and Rules here

Compaq Deskpro 286 Video Help

collector said:
that is the first thing I though of. The picture seemed to be better with the xt card and 5153 in the compaq but it was still unreadable. I will try the compaq card in the xt. If all else fails, is there another combination of card/monitor I can try? Maybe a 15 pin card?
Click to expand...

The Compaq card may well work fine in the XT, because the XT's motherboard BIOS will program it with frequencies that work on a 5153. Conversely, the XT card probably didn't work in the Compaq because the Compaq's BIOS was programming it with timings for the high-resolution text mode.
 
JohnElliott said:
Compaq CGA cards (in combination with a Compaq motherboard BIOS) support a high-resolution 350-line version of the 80x25 video mode. A 5153 won't be able to display this.

The CTRL+ALT+< key combination on the Compaq should switch to the normal 200-line version. On the 8086 Deskpro, it's possible to select this at boot time by turning on the motherboard DIP switch SW6. I don't know whether the 286 version does this with DIP switches or with a BIOS setup program.
Click to expand...

Good to know. I was not aware of this. so is the text better/sharper w/ a Compaq display?
 
JohnElliott said:
The Compaq card may well work fine in the XT, because the XT's motherboard BIOS will program it with frequencies that work on a 5153. Conversely, the XT card probably didn't work in the Compaq because the Compaq's BIOS was programming it with timings for the high-resolution text mode.
Click to expand...

That was going to be my next question: Why didn't the regular IBM CGA card work? How does the Compaq BIOS program the timings on the IBM card? I ask because if the card is a fixed freq. part then there is no timings to program. Or am I missing something?
 
thank you very much, tried the keystroke combo and it worked great. I am getting just black and white from my 5153. I have yet to try any type of program that might produce colors. Do you think I am restricted to bw because of the mb/vc combo?
 
It has been literally decades (well, almost two of them) but...

I'm pretty sure I had that exact card once. (I picked it up at a garage sale.) As has been clarified already in this thread, it was designed for use with a special dual-mode *monochrome* Compaq monitor that combined a high-res text mode with CGA graphics compatibility. Here's the thing I remember, however...

I can't make it out in the photos of the card, but I'm pretty positive there's a spot on the board where you can either add or remove a jumper and doing so will make it compatible with a normal CGA monitor. I used the card in a generic XT clone with that jumper set for several years. If there are any sets of staking pins on the board that look like they're for one of those standard little plastic jumpers try bridging them and see what it gets you.

(Edit: Wait, I guess if you're using the card in the original Compaq and are happy with the keyboard combination solution then it's probably irrelevant. Never mind.)
 
Last edited:
Shadow Lord said:
That was going to be my next question: Why didn't the regular IBM CGA card work? How does the Compaq BIOS program the timings on the IBM card? I ask because if the card is a fixed freq. part then there is no timings to program. Or am I missing something?
Click to expand...

The IBM CGA and compatibles are built around a 6845 CRT controller. The motherboard BIOS has to program the registers of this chip when setting the mode. An IBM motherboard BIOS only uses timings that the 5153 monitor can display, but others can be set up manually.
 
collector said:
thank you very much, tried the keystroke combo and it worked great. I am getting just black and white from my 5153. I have yet to try any type of program that might produce colors. Do you think I am restricted to bw because of the mb/vc combo?
Click to expand...

No; colour should be possible.
 
Eudimorphodon said:
It has been literally decades (well, almost two of them) but...

I'm pretty sure I had that exact card once. (I picked it up at a garage sale.) As has been clarified already in this thread, it was designed for use with a special dual-mode *monochrome* Compaq monitor that combined a high-res text mode with CGA graphics compatibility. Here's the thing I remember, however...

I can't make it out in the photos of the card, but I'm pretty positive there's a spot on the board where you can either add or remove a jumper and doing so will make it compatible with a normal CGA monitor. I used the card in a generic XT clone with that jumper set for several years. If there are any sets of staking pins on the board that look like they're for one of those standard little plastic jumpers try bridging them and see what it gets you.

(Edit: Wait, I guess if you're using the card in the original Compaq and are happy with the keyboard combination solution then it's probably irrelevant. Never mind.)
Click to expand...

The jumpers on the card are to disable the external CGA socket in the high-resolution mode. That's for when the card is in use in a Compaq Portable with the internal monitor attached to the header on the card. It's done with jumpers J3 and J5, which should both be set to the same position.

Pins 1-2: For Portable; the external CGA socket is disabled when in high-resolution mode.
Pins 2-3: For Deskpro; the external CGA socket is enabled when in high-resolution mode.
 
JohnElliott said:
The IBM CGA and compatibles are built around a 6845 CRT controller. The motherboard BIOS has to program the registers of this chip when setting the mode. An IBM motherboard BIOS only uses timings that the 5153 monitor can display, but others can be set up manually.
Click to expand...

Thanks for clarifying. Learned something new today!
 
You must log in or register to reply here.
Back
Top