RE: Where to start on Missile Command PCB repair

From: Matt J. McCullar <mccullar_at_flash.net>
Date: Thu Oct 31 2013 - 00:19:44 EDT

Howdy, Grant! I've worked on several "Missile Command" boards, and here's
what I've learned...

* Replace all the sockets. If yours are original, they are over 30 years
old now and their contacts are just as corroded as the pins on the chips.
Yes, it takes practice to desolder all those things effectively, but new
sockets will eliminate a great many headaches. (Replace the socket
underneath the 6502 processor, too.) [You may find some ripped-up
printed-circuit traces underneath these sockets; some people pry out those
chips without being careful, so you may have even more soldering to do.]

* Is the crystal still there? The main clock is generated from a 10.000 MHz
crystal, and all too often when I see a "Missile Command" board, that
crystal is just flat-out missing. Even if it's still there, it should be
solid in place and not easy to move around with your finger.

* I like to replace all of those old 4116 RAMs with newer 4164 RAMs, that
have been "tricked out" to resemble 4116's. You can find information on how
to do this on the Internet; it's not that difficult. The 4164 chips are
newer, use only +5 volts (instead of several bus voltages as the 4116s do),
and may be much easier to find on the market these days.

* A real curve ball: Atari designed the motherboard so that it could accept
two different kinds of EPROMs: 2708s or 2716s. There are lots of solder
pads (jumpers) next to the ROM sockets that tell the hardware which chips
are being used. You must look at these very carefully; a pad may be cut or
it may be intact (or resoldered). 2708 EPROMs use several bus voltages and
those pads must be configured for such; 2716 EPROMs hold twice as much
memory and use only +5 volts, but again those solder pads must be configured
for them. If the wrong type of EPROM gets plugged into a socket that
doesn't have those pads set correctly, it may destroy that EPROM. (I like
to "strap" the boards for 2716s, as they are far easier to obtain and work
with. If you have a "Missile Command" board that has EPROMs in every single
socket, they are probably 2708s; if only half the sockets are populated, the
chips are probably 2716s. But someone else in the past may have swapped
chips around without knowing the difference.) [If you use just 2716s, you
only have to replace half of the sockets!]

* Take lots of careful notes. Be sure the correct EPROMs/ROMs go in the
correct sockets.

Defend cities!

Matt J. McCullar

-----Original Message-----
From: owner-rasterlist@vectorlist.org
[mailto:owner-rasterlist@vectorlist.org]On Behalf Of Grant Thienemann
Sent: Wednesday, October 30, 2013 6:32 AM
To: rasterlist@vectorlist.org
Subject: RASTER: Where to start on Missile Command PCB repair

Hey Guys,

I've got a stack of Missile Command PCBs that don't work and I need
some guidance on where to start. Here is what I have done with my
first PCB.

Checked the PCB in test mode, doesn't nothing, just an audible hum
Felt all the chips to see if any are hot, none were warm to the touch
Replaced all the 4116 ram with sockets and cleaned the ram legs, still
nothing.

I have the following equipment at my disposal though honestly, I don't
know how to use some of it.

HP Logic comparator
HP 5004a <-- haven't used them yet
Atari Catbox <-- haven't figured out how to use it correctly yet
Fluke 9010a but no 6502 pod :-(
Logic Probe <-- haven't used it yet

Any information would be fantastic!

Thanks
Grant
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Received on Wed Oct 30 23:10:11 2013

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