Display issues with MFX 40 column basic

[davesnowdon]

I've noticed an odd display issue when using the MFX in SDX BASIC mode with the default 40 column display (I have build 167 of the MFX ROM)

The third screenshot shows a listing of drive D from SDX BASIC in 40 column mode. At first I thought that the contents of the SD card might be corrupt but later when looking at the disk from CP/M the file names were displayed correctly (second attachment). Running BASIC in 80 column mode (VGA1) also produces a clean listing.

This is not limited to just listing disk contents though. I can see the same issue when running "USER INFO" in 40 column mode (first attachment).

Any suggestions what the problem might be?

[Dave]

Hi Dave,


Mmm, that’s weird.

Are you able to hook a TV/monitor up to the MTX native video output, or even a TV coax? Does the problem occur there too, or is it only on the VGA output?

Regards
Dave

[davesnowdon]

Are you able to hook a TV/monitor up to the MTX native video output, or even a TV coax? Does the problem occur there too, or is it only on the VGA output?

I'll see if I can dig out a cable and find a display that will accept composite video. Will let you know

[Dave]

A couple of other quick suggestions . . . . .

Remove and refit MFX just in case the connector has worked a little loose.

Remove and reinsert the socketed chips on MFX, particularly the RAM and ROM

(Clutching at straws, but worth trying)

Regards
Dave

[Bill B]

According to the table on Dave's site, you have FPGA firmware version 1.01. With that version of the firmware, the 80 column display uses the FPGA internal RAM, and it is only the 40-column (VDP emulation) display that uses the external RAM.

So that very much suggests to me that the problem lies with the video RAM chip on the MFX. That is the large chip mounted horizontally above the FPGA board. So as suggested by Dave, I would first try gently removing and re-socketing that chip. If that does not work, try the same with the FPGA board itself (in case the connections between that and the RAM chip are unreliable). Beyond that I think it is trying replacing the video RAM chip.

[Martin A]

What does the Graphics mode output look like ?

If that ram chip has "gone" then there might be more corruption with G2 mode as there's that much more ram in use.

[davesnowdon]

Thanks all! I'll try graphics mode and re-seating the chips. I did try a couple of games when I first got the MFX and didn't see any issues.
Might be a couple of days before my next update - I need to finish a Halloween project.

[davesnowdon]

Sorry about the long delay in updating.

I got hold and a composite video cable and a monitor that can display composite video and this was the result.

IMG_0839.JPEG (921.65 KiB) Viewed 4375 times

For comparison this was the startup screen with VGA output

IMG_0840.JPEG (428.92 KiB) Viewed 4375 times

I guessing this means that it's not an MFX issue after all but possibly display RAM on the MTX itself?

[Dave]

Hi,

It’s almost certainly a VRAM fault. I suggest that you remove MFX and just use the MTX video output for faultfnding.

Although it’s not consistent, on occasion, it looks like the “‘“ is being displayed instead of a space. That’s probably ASCII code 96 instead of 32, I.e., a 1 bit error in bit 6. Could be a faulty 4116 in position 7G on the MTX board.

Although it’s unrelated to the fault, your MTX video board looks to be pinned for mono, rather than colour
The link option is described about half way down this page http://www.primrosebank.net/computers/ ... _board.htm

Regards
Dave