Re: Space Duel PCB weirdness

I've read the other responses to your question to date so I won't repeat
those. I know that there's likely a bad logic IC somewhere that isn't
gating or counting or shifting like it should, but that's hard to find
without special equipment so I'll give you a few simple hints that often go
a long way.

1/ I know that you said the clock is running but the main crystal or
oscillator circuit could still cause an issue if the levels aren't correct
or if the crystal broke and is running the wrong speed. Sounds weird, but
I've seen it happen. Also, check for the clock at other chips such as
counters, shift registers, latches, etc., not just at the CPU.

2/ Check the halt or reset pin of the 6502. See if it is being told to stop
and if so, backtrack that signal to be sure that the chips generating it are
getting what they need. If yes, then they are your problem.

3/ Replace the 2116's with 5116's or 6116's. Bad sram can cause weird
behavior and the game certainly won't run.

4/ Inspect those 377's again. Sometimes when people replace them, they rip
out vias and lose chunks of the traces on the component side under the new
socket. Beep them through from the socket contact through to their signal
destination/origin.

5/ Beep check the DIP sockets by measuring continuity from the chip pin (on
the shoulder/knee) to the pad underneath. Those old leaf contacts sometimes
snap/crack under the socket body near the PCB. If any doubts exist as to
the reliability of the socket, replace it... carefully and patiently. If
you have little soldering experience or don't have the proper tools for
socket removal, then don't attempt it. It's super easy to do more harm than
good when trying to remove multi-pin components. If you are proficient,
don't hesitate.

6/ If the board is really dirty, clean it thoroughly and don't be afraid to
get it completely wet. I wash my big boards and wiring harnesses in the
dishwasher with no ill effects, although certain residual soldering fluxes
(specifically no-clean type 245) can turn an ugly white. It can be removed
with simple rubbing alcohol and a toothbrush and/or q-tips. The point here
is that contaminates can prevent proper board operation depending on where
it is located. When I wash boards in the sink, I use mild hand soap and a
toothbrush or paintbrush to clean everything. I usually hold the PCB on
edge and drip dry for a minute, then either blow-dry with compressed air or
I lay it on a rack inside the clothes dryer and dry at lowest heat setting
for 45 minutes. I've never had a problem come up from doing this, and a
clean PCB is a happy PCB. Besides, I hate getting my fingers dirty while
working on boards anyway. If there's a ton of old rosin flux, it can be
removed with rubbing alcohol. The 70% works fine. The 99% works faster and
is stronger but also can cause some old solder masks to discolor but most
will be okay. The nice thing about rubbing alcohol is that it works, it's
cheap, and you can buy it almost anywhere. For really flux laden boards, I
fill a glass tray and set the board right in and let it soak for a while. I
gently brush it (with paint brush) while submerged until it looks clean and
then I drip dry for a minute and then blow dry it. I usually do this
outside in the open garage in the summer when it's warm. I would not
recommend exposing yourself to that much alcohol vapor indoors.

7/ Look at the entire board on both sides under magnification and the
brightest light that you have. Look for any sort of trace scratches that
has cut through and caused an open. Look for a broken trimpot leads, bent
or broken leads on resistors or diodes or anything. When a large part is
bent over (say a big film cap), it can hit and even break an adjacent
resistor. Check for broken SIP resistor networks. Check for DIP pins on
the bottom that are bent right over that may be touching adjacent pins or
traces. Oftentimes the problem is visually detectable if you have the
patience to really look over everything carefully. A lot of small damage
can occur when people carelessly stack their PCB's. I find this a very
common cause of failure on almost every sort of boards. People stack boards
and they either just don't care what happens to them or they are blissfully
unaware of what can happen. Either way, things get bent, broken, or
scratched. Also, check for any IC that is cracked, has a small hole or
crater or swelling right in the center of the body where the chip is inside.
When chips blow or fail, they can show such a physical defect and they can
leak black stuff out of the body along the lead frame and out onto a pin
where you can see it.

Dunno if that'll help, but good luck.

William Boucher

----- Original Message -----
From: "Chris Brooks" <armis@pcdochouston.com>
To: <vectorlist@vectorlist.org>
Sent: Monday, January 26, 2009 7:30 AM
Subject: VECTOR: Space Duel PCB weirdness

>
> Hello all - new to the list, but not arcade stuff :) Howdy from Texas!
>
> Anyway, I have a Space Duel board that is behaving badly and I am stumped
> as to what is going on.
>
> The watchdog barks, so I disabled it, then looked at the CPU bus. It
> appears to address memory for a few milliseconds, then completely stop -
> no
> activity, address bus locked, data bus locked. Clock looks clean on the
> scope and is operating at the correct frequency.
>
> I would completely understand this happening if it was a processor that
> supported halting or DMA, but the 6502 has no support for such things.
>
> Anyone have a clue on what to look at next? I'm thinking its time to
> invest
> in a logic analyzer.
>
> Thanks,
>
>
> Chris Brooks
>
>
> ---------------------------------------------------------------------------
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> ** Please direct other questions, comments, or problems to
> chris@westnet.com

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Received on Mon Jan 26 19:43:12 2009