TECH: Asteroids (Long Post)

Well I'm deep into repairing my asteroids game and I could use some
suggestions. When I turn the game on I get red LEDs on both the pcb and the
monitor board. The monitor is running (properly I believe) I think the
problem lies in the pcb, both of the player select LEDs are blinking rapidly
and an occasional hot spot appears on the screen but does not move and then
will disappear and reappear somewhere else. At one point I did get the test
patern up when I put it into self test, but I couldn't get this to repeat.

I put my ocilliscope probe on the X and Y test points on the pcb and over
the course of 5 minutes or so the signal would move from +.5 to -.25 to -1v
(these are gross approximations) at each level it would hold for 5 or 10
seconds and then change to the new level. These changes corresponded with
the hot spot changing its position, but it seemed to me it should have been
clocking much faster. I put the probe on the 6Mhz clock test point and was
able to see the clock, very ugly looking wave form, only a slight
resemblance to anything square.

I know this is a long post so thanks for reading the entire entry and any
help you can offer I would really appreciate. I may have forgotten
something so if you have any questions about specific details of the
machines opperation, post them and I will respond a.s.a.p. Thanks again for
any help you guys can provide.

Sincerely
Jeff Bovee

Update:

I checked the power at the board with my fluke meter and it read 5.04vdc
which seems pretty good. I also removed and cleaned all of the socketed
chips and cleaned the board edge connector. While I was doing this I noted
a blob of solder on the pcb and investigated further, only to find a really
botched up logic chip. It was a sn74161 and two of the legs had been busted
off and it looked like somone with a blowtorch had tried to reattach them.
Very poor workmanship, tsk... tsk.. tsk..

Well I dug out some of my electronics components from college and rummaged
through a tray of chips, and low and behold when I had almost given up, the
second to the last chip in the tray was a 74161, hooray! I desoldered the
old one and inserted the new. I wanted to stick in a socket instead of
soldering on the chip directly but the only socket I had was missing a leg.

After reconnecting the edge connector I powered it up, and still nothing.
Still no activity on the x or y outputs and the LED's on the player select
buttons have stopped blinking (don't know if that's good or bad). I could
really use some suggestions from any of you people who have worked on an
Asteroids pcb before. Thanks in advance for any help that can be rendered.

Best Regards
Jeff Bovee
Received on Wed Dec 30 07:23:32 1998