Quick Missile Command ROM question

modessitt

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I'm bench testing a -03 MC board. +5.10 at the chips. At first it was dead, but swapping in a good 6502 got it to come up, but it constantly resets when it goes to the attract mode after the title screen. Pokey has been verified as good, and all chips pulled, cleaned, and reseated. Disabling watchdog doesn't help either.

Put it into test mode, and I get BAD ROM 1,2,3.

Okay, so the manual says that means that the 1st, 2nd, and 3rd block of 2k memory are failing. However, it doesn't tell me how to identify which chip is 1st, 2nd, and 3rd. Looking at MAWS doesn't help, either, because it only lists 6 ROMs, while this board has 11.

My next step is to replace the sockets for those chips to see if that helps. If not, then I'll get 3 new chips. But I need to know which chips are 1, 2, and 3.

Any help?
 
Might check out page 39 (printed), page 45 (PDF here: http://arcarc.xmission.com/PDF_Arca...mmand/Missile_Command_TM-147_3rd_Printing.pdf).

That explains the difference between the 6 and 13 ROM versions (the -01 & -03 have 13, -02 and -04 have 6, like MAWS lists). I assume it's the same code, just some are split into two 1Kb for the "mostly PROM" versions of the PCB.

As far is which are 1, 2, 3... Look in the lower right corner of this: http://arcarc.xmission.com/PDF_Arcade_Atari_Kee/Missile_Command/Missile_Command_DP-147-2nd-01B.pdf

There are lines labeled ROM0/, ROM1/ etc., and 2KROM0/, 2KROM1, etc.. The former appear to refer to the split pads that select the 1K ROM option (i.e. -01 & -03 boards). The latter seem to be the designations for the PCBs with 2K ROMs (-02 & -04). It sounds like the self-test code 'assumes' the 2K option. So, if it's referring to "2K" ROM regions 1 2 & 3, that would seem to be J/K1, K/L1 & L/M1... on a -02/-04 board. The equivalent on you -03 board should be: J/K1, E1, K/L1, F1, & L/M1.

Or, of course, the (E)(P)ROMs could be fine, and if could be an issue in the address decoding.
 
True, but start with the simple steps first.

Would ROM0 be the first ROM (ROM1?) in test or would I go by the ROM1 signal? Looking at that schematic:

ROM0 - 035808 at H1
ROM1 - 035809 at D1
ROM2 - 035810 at J/K1
ROM3 - 035811 at E1
ROM4 - 035812 at K/L1
ROM5 - 035813 at F1
ROM6 - Combined with ROM7 to the 035823 at L/M1
ROM7 -
ROM8 - 035816 at N/P1
ROM9 - 035817 at M/N1
ROM10 - 035818 at R1
ROM11 - 035819 at R3

So, is the 035808 considered ROM 1 in the test mode, or would it have said 0 if that one would have failed.

And yes, I know I could just replace all 11 sockets, but I'd rather not have to for this board. Trying to do a cheapy repair for someone else with no money...
 
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I'd get rid of all the 2708's and replace them with six 2716's. There are jumpers on the board to do just that.

Great, but not very helpful. As I said, I'm trying to do a cheap-as-possible repair for someone else. And I need to know how to identify which ROM is which numbering-wise.

Since nobody is jumping in with a definite answer, I'm just going to replace the socket on E1 and see if it makes any difference on the self-test...
 
Interesting. Replaced the socket at E1 and now the error says ROM 2,3. Apparently that fixed the ROM 1 failure. Don't understand why that would happen based on what I saw from the schematics. Hmmm - which to try next...
 
Interesting. Replaced the socket at E1 and now the error says ROM 2,3. Apparently that fixed the ROM 1 failure. Don't understand why that would happen based on what I saw from the schematics. Hmmm - which to try next...

Makes sense to me. 2KROM1 is made up of ROM2 & ROM3, and ROM3 is at E1.

Try either K/L1 or F1 next (which comprise 2KROM2).

Or L/M1 (2KROM3).
 
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Makes sense to me. 2KROM1 is made up of ROM2 & ROM3, and ROM3 is at E1.

Try either K/L1 or F1 next (which comprise 2KROM2).

Or L/M1 (2KROM3).

Well, I replaced all 11 sockets (thank you, desoldering station) and still get the ROM 2,3 in test, and constant reset after title screen.

At one point, after replacing the socket for K/L1, the game wouldn't boot again. Tracked that down to the PROM at L6. Replaced that socket, and was back to where I was. When I replaced the socket for J/K1, the ROM 1,2,3 error came back, but went back to ROM 2,3 after replacing the M/N1 socket.

So, now what? It's either got to be as problem with the address decoding of the ROMs, or the ROMs themselves are bad (if I knew which was which).
 
Well, I suppose you'd need to concatenate pairs of your 1K ROMs to form 2K files, in order to compare with the MAME ROMs, if you wanted to go that route.

Or you could break out the logic probe start checking out the CS lines on the ROMS, and the outputs of the LS139 @ P2, and the 7408 @ R2.
 
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Well, for fun, I swapped the 7408 at R2 with the 7408 at J6, but no change. I did notice that at L/M1, I have a 8028 instead of a 2708 like the other spots. Accordingly, there are different jumpers so that - while the 2708's have voltage like:

Pin 19 - +12.4vdc
Pin 21 - -4.95vdc
Pin 24 - +5.09vdc

The 8028 has these voltages:

Pin 19 - +2.32vdc
Pin 21 - +5.09vdc
Pin 24 - +5.09vdc

Not that it might matter at all. Just letting y'all know.

I guess P2 and M5 will be my next suspects...
 
Can't find my damn logic probe at the moment, so I pulled both 74LS139N's at P2 and M5, put in sockets, and swapped them. No change. Still have ROM 2,3 and resetting at the same spot.

Gonna quit it for the night and try to find my logic probe in the morning....
 
Well, for fun, I swapped the 7408 at R2 with the 7408 at J6, but no change. I did notice that at L/M1, I have a 8028 instead of a 2708 like the other spots. Accordingly, there are different jumpers so that - while the 2708's have voltage like:

Pin 19 - +12.4vdc
Pin 21 - -4.95vdc
Pin 24 - +5.09vdc

The 8028 has these voltages:

Pin 19 - +2.32vdc
Pin 21 - +5.09vdc
Pin 24 - +5.09vdc

Not that it might matter at all. Just letting y'all know.

I guess P2 and M5 will be my next suspects...

Per the manual, the device at the L/M1 location was the same 2K chip for all revs of the board. Pin 19 appears to have only 2.32V on it because it's an address line in this case; pulsing between 0 and 5V. As far as the other voltages go... I can't find a datasheet for any "8028", but if it's similar to the "8316" in the schems, then those appear to be the correct supply voltages.

I'd suspect P2 more than M5.
 
Can't find my damn logic probe at the moment, so I pulled both 74LS139N's at P2 and M5, put in sockets, and swapped them. No change. Still have ROM 2,3 and resetting at the same spot.

Gonna quit it for the night and try to find my logic probe in the morning....

Dang. Well, you could continue going upstream... next stop, N2 (source of the PROGSEL lines). Or go back downstream... and read the data on those ROMs to see if you've got bitrot.
 
Well damn, stood up and saw my logic probe on the shelf. Anyway, probed M5 and P2. I'm not sure EXACTLY what i should be seeing and where, but some pins pulse rapidly while it's on title screen through until it resets, some pulse slowly through title screen then rapidly during the tiny amount of attract I get before it resets, and some pulse slowly all the time.

HOWEVER - pin 11 of M5 (ROM1) is stuck high.

Now, here comes the interesting part - I swapped the 74LS139N at M5 with the one at P2 to see if the stuck pin went with it. Nope. P2 is pulsing away on pin 11 just fine. Went back to M5 and found it pulsing away. But a few minutes later, I found pin 11 of M5 not pulsing and stuck high, while the board just boots and resets.

Didn't see any other pins on M5 that seemed to be a problem (all pulsed in some speed). so - now what?
 
More results - testing pin 20 of the 2708's (CS1), I find them all to pulsing except D1 and F1. They pulse a few times at start up then stay high....
 
The 7442s on MCs always seem to die or fail in a way that they appear to be working. Try piggybacking a few on the two 7442s to see if that helps at all.

Instead of replacing all of the sockets I would have switched to the 2716 solution and only replaced the six. I have had more problems with the 2708s that I don't even bother with them and immediately switch to the 2716s (or 2732s if you are out of 2716s). I'd try a different set of roms just for craps and giggles.

Let us know how you are faring. The way that the board is working makes me still think ROMs.

Bill
 
There are rarely any quick cheap fixes for MC. :)

(I know that doesn't help, sorry.)
 
The 7442s on MCs always seem to die or fail in a way that they appear to be working. Try piggybacking a few on the two 7442s to see if that helps at all.

Instead of replacing all of the sockets I would have switched to the 2716 solution and only replaced the six. I have had more problems with the 2708s that I don't even bother with them and immediately switch to the 2716s (or 2732s if you are out of 2716s). I'd try a different set of roms just for craps and giggles.

Let us know how you are faring. The way that the board is working makes me still think ROMs.

Bill

If I had another set of ROMs, or some 2716's (or others) I'd do that, but I don't. Trying to get this fixed quickly. I'll check the 7442's when I get a chance (tomorrow?)...
 
If I had another set of ROMs, or some 2716's (or others) I'd do that, but I don't. Trying to get this fixed quickly. I'll check the 7442's when I get a chance (tomorrow?)...

If you want a set to try, PM me with your mailing addy.

MCs can be maddening.

Bill
 
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