Missile Command not booting (Help me repair this board!)

TheDrewster

Well-known member

Donor 2012
Joined
Oct 5, 2008
Messages
7,668
Reaction score
314
Location
Reno, Nevada
Missile Command not booting (Help me repair this board!)

I just finished replacing the harness connector (what a bitch...) and much to my dismay, the board still does not boot. What makes this even more difficult is the fact that the monitor is shot and only displays bright green, so I cant see any video output. After poking around with my logic probe and multimeter, I know these facts:

Continuity from harness to edge connector is good
Board is receiving +5.02v
Player 1 and 2 lights constantly lit
Watchdog is high
Reset line is pulsing
Test mode does not work


Oy...Where do I start?
 
I just finished replacing the harness connector (what a bitch...) and much to my dismay, the board still does not boot. What makes this even more difficult is the fact that the monitor is shot and only displays bright green, so I cant see any video output. After poking around with my logic probe and multimeter, I know these facts:

Continuity from harness to edge connector is good
Board is receiving +5.02v
Player 1 and 2 lights constantly lit
Watchdog is high
Reset line is pulsing
Test mode does not work


Oy...Where do I start?

Does it go into test mode?

If it doesn't boot into test mode, check is if the CPU is getting clock. If it has clock but isn't booting, I'd start by cleaning and reseating all your ROMs. Then verifying them or swapping in a known good set.
 
Does it go into test mode?

If it doesn't boot into test mode, check is if the CPU is getting clock. If it has clock but isn't booting, I'd start by cleaning and reseating all your ROMs. Then verifying them or swapping in a known good set.

Throwing the test switch does not change anything, so I am assuming not.

CPU is getting a clock signal.

Reseating the ROMs did not help.
 
Throwing the test switch does not change anything, so I am assuming not.

CPU is getting a clock signal.

Reseating the ROMs did not help.

Did you clean the legs with a pink eraser, fiberglass pen, or similar?

Am I correct in assuming that the reset pin on the CPU continues to pulse when you put it in test mode?

I would swap in a known good ROM set next, or pull and verify the ROMs you have. If they're good, I would suspect the address decoders. Unfortunately, that's territory I haven't navigated before, so I don't know if I have much more to add.
 
I will pull the ROMs and verify them tomorrow when I pull my programmer + POS Dell laptop out of the tool bin. Ill report back with any findings.
 
If you are trying to troubleshoot the RAM circuitry (such as RAM itself, address decoders or data/address bus). It's helpful to have a Fluke 9010A. If you don't have one you still can do some testing.

First identify the RAM chips. Then pull the datasheets off the internet
for example if your RAM chips are 2114's then google "2114 datasheet"

Once you have the datasheet you'll want to identify the pins that that are labeld A0-Ax which are the address line pins, as well as the pins that are labeled as data input/ouput

while the board is "resetting" use a logic probe to test test of the address pins and data pins. Normally they should "flip" every so often, that is they will generlaly not remain constant high, low or "no-state" if you find that one of the pins does... it is likely a bad chip and needs to be replaced. If the RAMs all check out, then you want to get the schematics and locate the buffer chips that are immediately between the CPU and RAM chips. (chips such as LS244 and LS245 etc) These just have "inputs and outputs" for each pin... that's an input or an output... test it the same.

again if you just find one pin on a chip (in the input, output, address, or data etc) that's not "flipping" that chip is probably bad. (keep in mind though you cannot just test "every pin" for example the ground, will always be low, Vcc will always be high etc.

hope this helps. If you want to try to troubleshoot this, let me know I think I have millipede schematics somewhere, and can help you figure out which chips to look at.

-brian
 
Back
Top Bottom