Re: Where to start on Missile Command PCB repair

It could be bad and would explain why watchdog isn't running (voltages are
acceptable). A 'scope would show if outputs are toggling, but a voltmeter
to B4 pin 3 will work just as well, it should be around 2 volts.

On Thu, Oct 31, 2013 at 11:15 PM, Grant Thienemann <
grant.thienemann@gmail.com> wrote:

> Ok,
>
> On Pin 37 I saw a constant 1.971 volts.
> On Pin 40 I saw a constant 3.7 volts
>
> And I noticed this chip is getting hot to the touch in the pictures below,
> is the one that is brighter than the others
>
> [image: Inline image 1]
>
> Which if I'm reading the schematic correctly is a 74191. It was just by
> chance that I noticed that chip was warm, to the tips of my fingers I
> didn't notice it but on the back of my hand, I thought it was hot.
>
> Thanks
> Grant
>
>
> Suggestions:
>
> Processor is 6502A, NOT 6502. Make sure someone didn't stick the wrong
> chip in there.
>
> You can go low-tech if you want, take your DVM and measure processor pin
> 37. If the clock is there it should read around 2.5 volts. 0 or 5 means
> clock is missing.
>
> Measure pin 40 (NRESET). If 0 volts you're stuck in reset. If around 5
> volts either game is running or watchdog isn't working. Should be pulsing
> between 0 and 5.
>
>
>
>
> On Thu, Oct 31, 2013 at 8:57 PM, Grant Thienemann <
> grant.thienemann@gmail.com> wrote:
>
>> Hey Guys,
>>
>> So I replaced the 6502 socket and all the EPROM sockets as well, did a
>> quick check and the crystal is on the board, though I have no idea if its
>> good or not.
>>
>> Anyway went to turn on the game and I don't get a loud hmmm anymore, but
>> nothing is appearing on screen and the game still appears to be dead.
>>
>> I need to either figure out how to use my catbox, find a 6502 pod, OR
>> find my logic probe . . .
>>
>> -Grant
>>
>>
>> On Thu, Oct 31, 2013 at 9:02 PM, Matt J. McCullar <mccullar@flash.net>wrote:
>>
>>> **
>>> Nice work so far, Grant. Here is where you can find images showing how
>>> to "strap" _Missile Command_ boards for different EPROMs:
>>>
>>> http://www.ionpool.net/arcade/atari/MC2708.jpg
>>> http://www.ionpool.net/arcade/atari/MC2716.jpg
>>>
>>> You can modify each one of the 4164 RAM chips to "behave" like a 4116.
>>>
>>> How to use a 4164 chip instead the original 4116:
>>>
>>> - Bend pin 1 und 8 upwards so they no longer go into the socket's
>>> connectors.
>>> - Connect Pin 8 and 9 with one another through a short piece of
>>> wire.
>>> - Make sure pin 1 and 8 are not in contact with any other components
>>> nearby.
>>> - Insert the chip like this into the socket.
>>>
>>> (Some gamers who own Williams games like _Defender_ have zillions of
>>> these RAMs to modify, and it's a lot easier for them to just modify the
>>> board rather than all the chips. _Missile Command_ doesn't have very many,
>>> and that's why I like to just upgrade the chips instead.) You do not have
>>> to change any jumpers on the _Missile Command_ motherboard for this.
>>>
>>> I don't have a _Missile Command_ board within arm's reach right now, but
>>> the crystal is probably labeled "X1" on the motherboard. It looks like a
>>> small rectangular silver can. (Unless it's missing!)
>>>
>>> Hope this helps!
>>>
>>> Matt J. McCullar
>>>
>>>
>>
>>
>

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Received on Fri Nov 1 00:28:13 2013