A2286 Bridgeboard Tseng ET4000 VGA issues

[hawkman]

Hi everyone, I've been working through the many issues on my A2286 bridgeboard setup (XT-IDE solved, see here) and now I'm down to my last but possibly most frustrating issue.

I have soldered in the two 16-bit ISA connectors into the A2000 so I now have three 16 bit slots available. First has the XT-IDE, second a Soundblaster Vibra16C (working) and the third a Tseng ET4000 card with 512mb RAM. System boots correctly and color text mode is fine on the monitor connected to the VGA card.

However, graphics are a mess. Windows 3.1 sort of "duplicates" things and there is a lot of graphical garbage. Games that I've tried so far show gibberish.

I ran Checkit's Video RAM test and it always fails with the exact same errors, see attached. I've unsoldered the lower 256K of the card and socketed it, swapping the upper 256K in and even changing the order of the memory chips. Same exact error every time, with the same data. I therefore don't believe it's a bad memory chip. If it were a memory controller issue, I would imagine that the results would be random rather than exactly the same each time.

My suspicion is that something is using the lower part of A000 for its own nefarious purposes and corrupting the VGA memory space, however a review of Checkit's memory map (also attached) shows only the VGA card in that 128K space, which is where it should be. This seems normal.

I'm still recalling the old days of DOS and device drivers, but I can't recall a situation where something would step on VGA memory space. I have the bridgeboard memory set to D000 so I don't believe that's it, but I'm running out of ideas of what else it could be.

Unfortunately, this is the only PC with ISA slots I have access to, so testing the VGA card in another machine isn't an option right now.

Does anyone have any suggestions?

[Jope]

Have you disabled mono and colour video in PCPrefs?

I'm guessing technically the emulated mono video could coexist with a physical VGA board, just like you can plug in VGA and MDA into a real PC.

[hawkman]

I have tried that, yes. But then the system doesn’t boot. It gets stuck at where it tells me that the parallel port is at xxxx and then it doesn’t progress. I have tried all 4 settings in the 4.2 BIOS - color 80, color 40, mono and special - and none of them seem to allow it to boot.

** edit **

I should also point out that the A2286 came with BIOS 3.5, which I have since upgraded to 4.2 by flashing some new EPROMs. If it's a BIOS issue, I have the equipment to re-flash to any available BIOS.

[hawkman]

Here's a follow-up, although I have still not found an acceptable solution yet.

The system refuses to boot either the XT-IDE or the hardfile unless *both* color and mono are enabled in PCPrefs. I tried disabling the Janus handler and that doesn't allow me to boot with either of mono or color disabled.

However a weird thing happens with I boot with A000 as the Janus handler memory, the system boots with the VGA display flashing yet it passes Checkit's VGA test. I expected there to be graphical issues because of course A000 is where VGA lives in the memory map but I didn't expect it to pass the VGA memory test. Windows is however still a mess although in a different way.

So the only bootable situation still remains D000/color on/mono on in PCPrefs.