Re: Where to start on Missile Command PCB repair

Yeah, still can't believe I did that one, kind of mind blogging because
I've built easily over 20 computers, and I've been working arcade PCBs now
for over a year.

ANYWAY onto my second Missile Command PCB, having learned from my prior
experience, I did the following:

1st. Installed sockets all the ram chips
2nd. Replaced sockets for 6502A and PROMs
3rd. Installed new 4116 ram onto the board
4th. This board actually had a 6502B processor instead of 6502A, but seeing
at it was rated at 3Mhz instead of 2Mhz and I figured the clock would
regulate it I installed the 6502B back onto the PCB.

At this point I tried the PCB, and I was getting the game rebooting after
main Missile Command screen. Went into test mode and I got that the RAM was
good but the ROM was bad. So I got out my Needham's EMP-30 and read all the
PROMs onto my computer, did a romcmp with MAME and found that 035824-02
PROM was bad, even after cleaning the chip, I wasn't getting any data from
it, so I pulled another 035824-02 PROM and installed it on the board, and
the game booted. I played games on that PCB for about 2 hours last nigth
with no issues.

I started working on my third Missile Command PCB by removing 6502 and some
of the PROM sockets but it was late. I will try finishing up that PCB
tonight.

-Grant

On Mon, Nov 4, 2013 at 11:48 PM, matt <galaga@slingshot.co.nz> wrote:

> 5th. Installed new ram backwards <- yup
>
> backwards I killed my Atari 400 by putting the ram card and CPU card
> backwards!!!
> and the 6502 pod wont test say's addess line stuck???
>
>
>
> On 5/11/2013 9:11 a.m., Grant Thienemann wrote:
>
> UPDATE
>
> So I have a stack of these PCBs to fix, this first Missile Command PCB I
> was fixing was out of my upright. Turns out these were issues:
>
> 1st. 6502 and not 6502A
> 2nd. 2 bad EPROMs
> 3rd. Bad sockets for Pokey, 6502 and EPROMs
> 4th. 3 of the 8 4116 ram chips where bad
> 5th. Installed new ram backwards <- yup
>
> I installed sockets for the new ram so that helped significantly with
> changing them out. I have the voltage set right at 5.02 volts, though I
> would like to get the negative voltage down below -5.2 volts, not sure how
> to go about fixing that on the ARII pcb.
>
> The game now works fine. I got lucky on this one honestly. For my second
> PCB I went ahead a put new sockets on the PCB for the ROMs, 6502A, Ram and
> Pokey. I installed new 4116 ram last night as well, just didn't get around
> to testing it, I will try the PCB out this evening.
>
> I'll keep ya'll updated! Thank you so much everyone for you help!
>
> -Grant
>
>
> On Fri, Nov 1, 2013 at 7:54 PM, <solarfox@triluminary.net> wrote:
>
>> On Fri, 1 Nov 2013 08:08:42 -0500, you wrote:
>>
>> >On Nov 1, 2013 7:52 AM, "Grant Thienemann" <grant.thienemann@gmail.com>
>> >wrote:
>>
>> >> Ok not to keep getting off topic, but as this is related to the Missile
>> >> Command repair, I'm going to ask. When I look for 74191 I can't find
>> >> anything on Digikey, etc, but when I search for 74HC191 it comes up, is
>> >> that the same thing?
>>
>> >Close. HCT is closer. Either should work.
>>
>> Not always, though. 74HC is "high-speed CMOS"; its switching thresholds
>> for what it considers "low" and "high" logic levels are the usual <33% of
>> Vcc = Low, >66% of Vcc = High. In a 5Vdc circuit, this works out to
>> <1.65V
>> = Low, >3.3V = High.
>>
>> However -- TTL gate inputs consider anything <0.8V to be "low", and >2V to
>> be "high". On the output side, 0 - 0.5V is considered an acceptable "low"
>> output signal level, while 2.7V - 5V is an acceptable "high."
>>
>> So -- mixing 74HC with TTL *may* work. It will *probably* work. It would
>> take a very unlucky coincidence of worst-case scenarios for the input and
>> output drive voltages of the two different chips to fall within the
>> "mismatch zone"... but it *can* happen.
>>
>> 74HCT, on the other hand, is "high-speed CMOS, TTL-compatible"; it's
>> specifically designed so that its input and output signal levels fall
>> within the same ranges as "normal" TTL.
>>
>> -----------------------------------------------------------------------------
>> A: Because it reverses the natural flow of conversation.
>>
>> Q: Why is top-posting bad?
>>
>> -----------------------------------------------------------------------------
>>
>>
>> ---------------------------------------------------------------------------
>> ** Unsubscribe, subscribe, or view the archives at
>> http://www.vectorlist.org
>> ** Please direct other questions, comments, or problems to
>> chris@westnet.com
>>
>
>
>

---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Tue Nov 5 09:42:09 2013