(Topic ID: 313304)

DESW: DMD ROM, socket all pins?

By mcmnky

4 months ago



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  • 5 posts
  • 3 Pinsiders participating
  • Latest reply 4 months ago by Dmod
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27040 (resized).PNG
DMD_board_after (resized).JPG
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#1 4 months ago

I'm replacing the stock display on my Star Wars with ColorDMD and notice a pin on the display ROM sticking out from the socket. Do I leave it like this or fix it?

My first thought is obviously reseat the ROM, but my second thought is, it's been working with this configuration. Maybe this was done on purpose. The DMD is working, I'm just replacing it to get colors.

What do you think--don't rock the boat or do the hustle?

PXL_20220409_192553366.MP (resized).jpgsketch-1649533739968 (resized).pngsketch-1649533712937 (resized).pngsketch-1649533767653 (resized).png
#2 4 months ago

That board looks pretty sad, was the game in a flood?? In the schema U12 pin 1 is marked as the 5v so how that's functioning properly is beyond me.

pasted_image (resized).png

#3 4 months ago

No flood just dirty.

I think I'm going to leave it and finish putting the ColorDMD tomorrow. One, it's working. Two, the more I look at it the more I'm convinced that pin will break off if I tried to get it in the socket.

If the new display doesn't work I know where to start troubleshooting.

#4 4 months ago

Lewis Carroll's White Queen, who said "why, sometimes I've believed as many as six impossible things before breakfast" might have been the previous owner of this machine.

I finished the ColorDMD installation (without doing anything to the ROM), updated the display firmware, fire it up, and no display. I can bring up the display configuration menu, but no game animation.

So I know when working with these boards it's important to check, double check, triple check that all cables are connected correctly. The ColorDMD instructions are somewhat ambiguous (install with the red stripe to the right--is that my right or the board's right?) so at first I had the ribbon cables matching the original configuration.

On inspection I noticed the ribbon cable from the display board to the LED board has the red stripe at pin 14. Doesn't the red stripe usually go to pin 1? So I reverse that cable, fire it up, and it works!

So what, you're thinking. That the display doesn't work with a cable in the wrong orientation and works with the correct orientation isn't quite a news flash. OK, but how was the original display working with the cable in that original orientation?

In the "before" picture both ribbon cables have the red stripe to the left.

DMD_board_before (resized).JPG

After, the 26-pin ribbon has the red stripe left, while the 14-pin ribbon has red stripe right.

DMD_board_after (resized).JPG

The display ROM continues to have that 1 pin out of the socket, as it's been since I got the machine about a year ago. I try not to think about it too much, as long as it works.

#5 4 months ago
Quoted from mcmnky:

Lewis Carroll's White Queen, who said "why, sometimes I've believed as many as six impossible things before breakfast" might have been the previous owner of this machine.
I finished the ColorDMD installation (without doing anything to the ROM), updated the display firmware, fire it up, and no display. I can bring up the display configuration menu, but no game animation.
So I know when working with these boards it's important to check, double check, triple check that all cables are connected correctly. The ColorDMD instructions are somewhat ambiguous (install with the red stripe to the right--is that my right or the board's right?) so at first I had the ribbon cables matching the original configuration.
On inspection I noticed the ribbon cable from the display board to the LED board has the red stripe at pin 14. Doesn't the red stripe usually go to pin 1? So I reverse that cable, fire it up, and it works!
So what, you're thinking. That the display doesn't work with a cable in the wrong orientation and works with the correct orientation isn't quite a news flash. OK, but how was the original display working with the cable in that original orientation?
In the "before" picture both ribbon cables have the red stripe to the left.
[quoted image]
After, the 26-pin ribbon has the red stripe left, while the 14-pin ribbon has red stripe right.
[quoted image]
The display ROM continues to have that 1 pin out of the socket, as it's been since I got the machine about a year ago. I try not to think about it too much, as long as it works.

The red stripe on the cable is a guide that usually runs from pin 1 on one connector to pin 1 on the other end, but if it was an after-market cable it's possible it was assembled with pin 1 running to pin 14. Cables can be ordered/assembled either way.

With the standard cable, it's possible the cable was installed reversed at both ends (red stripe on pin 14 at both DMD and display board) which will also work.

As far as the EEPROM, pin 1 (VPP) is the programming voltage pin and isn't used during reads on a 27C040 EEPROM. It's a don't care when the EEPROM is in read mode, which is why it's working despite not being installed correctly.
27040 (resized).PNG

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