Tech: Centipede Board sprite issues
LyonsArcade
I've got a Centipede PCB that was working fine until this morning,
now all of my moving objects have the picture in the wrong order going
left to right... i.e. the 'ship' has the right side over to the left,
then a few lines of air, then the right side of the ship, then a few
lines of air, then the left side of the ship. Up and down everything
is fine, just horizontally it's out of order. The playfield looks
fine, it's just the moving objects. I've tested both the character
roms and they're fine, and I don't get any 'beeps' in the self test
although I think that just tests the playfield ram, and the playfield
looks perfect.
Any ideas where to poke around next?
Thanks in advance!
Craig Yarbrough
Most likely a problem in the Motion Object circuitry. Check the adders
@ F6 and H6 - those are notorious for going bad. Also the '163
counters @ A5 and B5, although IIRC if those go bad the objects start
disappearing.
I do work on these if you find you need help.
- Craig
LyonsArcade
Craig, thank you for your help. I ordered those parts from Jameco
(but it looks like they take a couple weeks to ship? WTF?) ... I'll
reply back after I figure out where we are on it!
Thanks again
Ron
LyonsArcade
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I never got the parts from Jameco, so I took an old parts board I had
and stole parts off of it. I did F6 (with a socket) and noticed a
slight change, then did H6, no change... then did A5 and B5, no
change, then went back and looked at F6, there was a pin bent! Fixed
the pin, fixed the problem. You're pretty good Craig, I'll bet you've
done that a few times, eh?
I've got another one i'm messing with that I thought maybe you might
have an idea about, if you're game. The board works perfect, except
for the first 10 minutes or so, there's a jitter from side to side.
It's the entire image almost like the vertical on the monitor is
collapsing. I've tried it in two different cabinets and it does it in
both... when you put it in 'test', ... the test screen never shakes at
all. If you go back out of test (and the machine's only been on less
than 10 minutes) the shake is still there. It's only once every 30
seconds or so. I replaced a couple things in the vertical sync
circuit but really I don't think it's in the sync circuit because it
doesn't do it in test. I'm thinking maybe it's in the playfield
stuff? It's hard to figure out because once the game is on for 10
minutes or so, it doesn't do it. It's not cabinet related becuase
other pcb's (like this one I just fixed!) work fine in the cabinet,
and the jittery pcb does the same thing in a different cabinet. Just
for giggles (before I figured out it didn't do it in test!) I rebuilt
the monitor, and put a brand new bob roberts big blue/black in the
bottom. Cleaned fuses, all that stuff, checked the power coming in
from the a/r, etc. I've cleaned the edge connector, checked
continuity, etc. and again it only does it when it's in play, and the
test screen is steady as a rock. The jitter is only about a quarter
inch or so from side to side, it would be the vertical circuit on the
monitor, I don't know which it would be on the pcb.
Thanks again, you guys are lifesavers!
Ron
Craig Yarbrough
Glad I could help out! :-)
That other problem sounds like it might be a bad socket at the sync
PROM P4.
- Craig
LyonsArcade
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Thanks Craig, I tried replacing that chip but I'll try putting a new
socket in as well.
If I find out anything I'll update the post (in case anybody ever
searches this stuff!)
Ron