Gravitar Troubleshooting

From: Tim Tewalt <tim_at_tewalt.com>
Date: Mon Sep 29 2003 - 17:50:49 EDT

I have a Gravitar board that won't boot. I replaced the overheating RAM
with 6116's but it still ain't woikin'.

Diagnosis has been painfully slow, so to help isolate the failure, I
swapped all socketed parts (CPU, RAM, PROM'S and three, I think, 40-pin
Atari custom parts) and put them in a Black Widow board. The BW board came
up just fine (except now it played Gravitar). Now that I think of it, I don't
think I swapped the EAROM.

On the bad board, the #WDCLR line pulses low about four times in rapid succession, then stays high for a while which results in a reset. On the good board, #WDCLR pulses low less frequently and in a more predictable fashion.

No address lines are stuck... they toggle, but are jittery and kinda seem "confused". Address lines on the good board are stable.

The data lines look like a mess. When they are tri-stated, should they go high
or low? D7 looks particularly bad. There seems to be some data bus contention on this line. I removed the socketed parts and noted it still toggles. D0-D6 are all low. Before stopping for the day, I had found the #SINP2 line pulsing. I didn't trace this back, but wonder how this could be if the CPU was removed. With the CPU removed, all the address lines should be low, right?

Is removing the CPU and memory devices an accepted method of troubleshooting? Or, will I most likely go in circles again due to the undriven lines?
---------------------------------------------------------------------------
** To UNSUBSCRIBE from vectorlist, send a message with "UNSUBSCRIBE" in the
** message body to vectorlist-request@vectorlist.org. Please direct other
** questions, comments, or problems to chris@westnet.com .
Received on Mon Sep 29 17:50:56 2003

This archive was generated by hypermail 2.1.8 : Mon Sep 29 2003 - 18:50:01 EDT