RE: Asteroids troubleshooting

Piggyback will work depending on the failure of the chip. If it is an open
bond internally then this will show that. If it is a short it might still
show improvement if the new chip can overdrive the failure.

I have an HP 1672 and have tried using it a couple times, trick is figuring
out how to setup the triggering to get a capture that makes sense. So far
it hasn't helped me find anything.

David

-----Original Message-----
From: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org] On Behalf Of Douglas Gauck
Sent: Monday, December 19, 2011 10:04 PM
To: vectorlist@vectorlist.org
Subject: Re: VECTOR: Asteroids troubleshooting

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 02:19:16 2011