Missile Command -Single Rom Mod

orion3311

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Me and theBman are here trying to burn up some Missile Command PCBs -mine has the second rom enable line being flaky and his, well I think all but 2 roms are bad. I have some 27128's and want to do a single rom mod on these to see if we can get em working.

Anyone know how the address lines should be hooked up to make them work?
 
Thanks - got the roms working at least. I was pretty close except we didn't have the roms burned backwards and didn't use the second rom. You'd think there'd be a way to use only a single - possible tying an address line to the progsel lines but not sure there.

This board is a doozy...bad roms...rams work sometimes, then don't, then do. Now its showing a short on the data bus yet the rom tests still pass. Must be a 244 issue.
 
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Thanks - got the roms working at least. I was pretty close except we didn't have the roms burned backwards and didn't use the second rom. You'd think there'd be a way to use only a single - possible tying an address line to the progsel lines but not sure there.

Well if you tie all the data lines in one bank of ROMS to the data lines in the other bank of ROMs, you can get away with using a single ROM, but that's just ugly.

Otherwise you have to disable one of the 74244s and either add logic (or just do a diode-resistor wired OR) to generate an enable for the other 74244 for tne entire bank of ROMs.

This board is a doozy...bad roms...rams work sometimes, then don't, then do. Now its showing a short on the data bus yet the rom tests still pass. Must be a 244 issue.

Pull all the 4116's put in sockets and replace them with 4164s. Traces on MCs suck, so you might want to cut the chip out to make sure you don't rip any up.
 
Anyone have a link on swapping out the 4164 ram? Doesn't look hard at all for this board..just install sockets leaving pin 9 out, and switching the 12v bus to 5v, but I can't find where the hell the 12v bus is fed from. I see the electrolytic at the edge but the opposite end goes to ground as expected (as a filter)...where is it supplied from?

This is a nice writeup on the pinout at least...

http://osiweb.org/osiweb/misc/4116to4164.txt
 
Here ya go:

http://www.robotron-2084.co.uk/gifs/4164hack.gif

No need to cut traces on the board either.

Cheers! :)

Anyone have a link on swapping out the 4164 ram? Doesn't look hard at all for this board..just install sockets leaving pin 9 out, and switching the 12v bus to 5v, but I can't find where the hell the 12v bus is fed from. I see the electrolytic at the edge but the opposite end goes to ground as expected (as a filter)...where is it supplied from?

This is a nice writeup on the pinout at least...

http://osiweb.org/osiweb/misc/4116to4164.txt
 
Hmmm a little simpler than I would have come up with.

Hacking up 8 chips isn't particularly smart. It's much cleaner to mod the board.

Unless you're using 2708s eproms, you can cut the -5 and +12 after the LM324, as it and the 4116s are the only other parts that use them.
 
Had only a minute tonight to glance at it again with a bright light, and now I see the one passthru connecting the 12v bus for the rams to the bus that runs down the center of the board, which goes directly to the edge connector. Man if that 12v really does just run the rams and roms, should be a piece of cake to just pull a pin out of the edge connector and make a jumper for 5v on that pin.
 
Had only a minute tonight to glance at it again with a bright light, and now I see the one passthru connecting the 12v bus for the rams to the bus that runs down the center of the board, which goes directly to the edge connector. Man if that 12v really does just run the rams and roms, should be a piece of cake to just pull a pin out of the edge connector and make a jumper for 5v on that pin.

It would be wise to mod the board such that it would continue to work when plugged into the standard harness. Otherwise you could smoke someone's PS down the road if they put your board in their machine. And you wouldn't have to muck around with your harness if you needed to test another board in your machine.
 
Thats true - in both our cases we don't have cabs, just the dream of one some day, so for now we just wanted to make sure the boards worked.
 
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