Don't know if this will help but here's an old post of mine
from repairing a few Asteroids boards, lots of DAC-lookalike
trouble with the TL081, TL082's, 4016's.
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G'day everyone,
I just repaired 5 Asteroids boards, and thought this time I would
write down a bit of a repair log to document it, here it is,
please feel free to do with it as you please.
As you can see, it's probably not a bad idea to remove, socket (good
machined sockets)
and replace the TL081, TL082 and 4016 IC's in the X and Y output section,
it'll probably save some trouble later and they're very cheap and easy to
replace.
I also replaced a 4016 in the sound section for a missing sound, but can't
remember which one it was...
I used a CRO in XY mode for a monitor, with no Z input set up. The missing
objects and fault areas common to the TL082's showed up as angled egg/oval
shapes,
about 5 times larger than the missing object, as on the CRO with no Z you
can see all deflection even if fast or if Z is off.
I must say thankyou very much to Tom McClintock, Phil Morris, and
'frankk@sympatico.ca' for the great Asteroids Repair Encyclopedia!
http://www.ionpool.net/arcade/asteroidtech/asteroidsrepair.html
It was very handy and the /DMAGO tip (lift pin 1 of 74LS42 @ L6)
for isolating the VSM vs. CPU fault area was invaluable.
Cheers,
Marc
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Asteroids repair log Marc Alexander June 2003
All boards were Asteroids Rev 4, A034986-04
Pulled socketed IC's on all the boards first, cleaned the legs
with a pencil eraser and scraped where needed, sprayed contact
cleaner into socket pins and scrubbed IC's in and out a few times.
Socket inspection was ok, but if yours look bad then replace them first :)
Used ink (grey) side of pencil eraser on edge connectors and
rebuilt missing/burnt edge connector copper with adhesive copper strips
wrapped around and soldered on power pin sections.
All DIP switches set to on, (red stripe down) just for test compatibility
and free play mode on.
Board 1
No self test, no output
12.096MHz crystal missing, replaced
Board still not running
74LS393 @ B4 tested faulty and replaced
Board does repetitive single high pitched beep in self test,
(watchdog is causing repetition of high pitched beep)
(passing RAM/ROM self test just gives single beep in self test)
Socketed and tested 74LS42 @ L6, lifted pin 1 (/DMAGO) out and ran self
test, now got single 'ok' beep in self test, game now plays blind,
meaning VSM (Vector State Machine) not working, but CPU section ok.
PROM @ C8 faulty (82S129 type)
After much other logic IC testing and scoping, where PROM outputs
looked ok visually on CRO, swapped out anyway with one from another
working board, and the part was faulty.
In play, objects on screen disappear, mostly top left and left side.
TL082 @ C12 faulty
4016 @ D12 faulty
The TL082's at C12 and A12 are the final output drivers of the
X and Y signals to the monitor. Any voltage offset or power
problems between the monitor and game board probably kills these
first!
Board 2
Crystal bent over at an angle, not oscillating
12.096MHz crystal replaced (used 10MHz for testing, had no more)
PROM at D/E1 dodgy wobbly leg, broke off on removal.
Replaced with 2716 programmed to suit
No X and Y deflection out, just small wobbly DC offset.
TL082 @ A12 faulty
TL082 @ C12 faulty
4016 @ D12 faulty (was causing slightly wobbly vectors)
The TL082's at C12 and A12 are the final output drivers of the
X and Y signals to the monitor. Any voltage offset or power
problems between the monitor and game board probably kills these
first..
Saucer sound too high in pitch
47nF greencap at C46 replaced
Board 3
No self test, no output
PROM at C1 tested faulty (swap test with working set),
Replaced with 2716 programmed to suit
In play, objects on screen disappear, all over.
Self test only draws angled vectors, vertical and horizontal lines
'fuzzy'
TL081 @ E12 faulty
TL082 @ A12 faulty
TL082 @ C12 faulty
4016 @ D12 faulty
4016 @ B12 faulty
The TL082's at C12 and A12 are the final output drivers of the
X and Y signals to the monitor. Any voltage offset or power
problems between the monitor and game board probably kills these
first..
4 smaller PROM's in H2, J1, M2, M1, but also larger (2716 type) PROM
in D/E1. I thought the 4 smaller PROM's were replaced by the larger
PROM,
so the smaller ones were removed and board still fine. Some swapping
around and testing confirmed this, either combination was fine, both
set(s) were being read, and returned the same data.
I guess a previous op/repairer must have done this.
4 smaller PROM's removed.
Board 4
In play, objects on screen disappear, all over.
TL082 @ A12 faulty
TL082 @ C12 faulty
The TL082's at C12 and A12 are the final output drivers of the
X and Y signals to the monitor. Any voltage offset or power
problems between the monitor and game board probably kills these
first..
Board 5
Crystal missing
12.096MHz crystal replaced (used 10MHz for testing, had no more)
In play, objects on screen disappear, all over.
TL082 @ A12 faulty
TL082 @ C12 faulty
The TL082's at C12 and A12 are the final output drivers of the
X and Y signals to the monitor. Any voltage offset or power
problems between the monitor and game board probably kills these
first..
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Received on Mon Sep 12 19:54:21 2005
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