I was looking for validation of the method of piggybacking a chip to troubleshoot.
Piggybacking a different chip onto J5 didn't work because of bad luck - the new chip was bad.
I picked K3 to pull first, and the output of J5 started pulsing. But a new LS157 at K3 brought it back to 0. Seems the output of the LS193 at J5 would work going into one chip but not both K3 and J4.
Original LS157 at K3 and new LS193 at J5 brought ADMA11 back to life.
Didn't fix the image - that turned out to be a bad LS191 at F9, found by comparing pin for pin with C9. The test diamonds weren't missing, they were being drawn over top identical neighbors above or below.
-Douglas
On Dec 14, 2011, at 9:34 AM, Douglas Gauck wrote:
> Hi all,
>
> I've gotten a dead Asteroids board most of the way back to life; game is playing but some objects are missing (and an incomplete diamond field in self-test). Self-test passes and all signatures in Peter Fyfe's asteroids_sa guide appear as they should. Since the vectors that are drawn appear good (right size, place and brightness) I thing the vector timer section is good. I may have a problem in the X/Y position counters but it feels more like the VG is just skipping some drawing. So I checked the program counter section and found ADMA11 is stuck low (but not grounded). That comes from J5 pin 6 and goes to J4 (LS670) pin 2 and K3 pin 3 - so how can I determine which one is dragging down the level? I piggybacked another LS193 on J5 with pin 6 bent out, figuring the new chip would leech power and inputs and give me a good output on dangling pin 6... but it's still low. Is there a flaw in my reasoning or method? Any ideas on other approaches or causes?
>
> -Douglas
>
> PS. Have a scope, 5004A and have been using the parallel port on an old PC as a down & dirty logic analyzer but am thinking of getting a Tek 1241 or HP 1650. Any thoughts on a good LA would be appreciated (newest game in my collection is from 1986)
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Received on Tue Dec 20 01:03:51 2011
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