I took out the GAL and all the resistors and basically hardwired the CPU in as a stock setup, and it still does not work..
So I am back to thinking this is sort of bad connection fault again.. Though I do not like getting into these "going around in circles" problems. I guess it is possible these PCBs are simply rubbish..
I got my regular PCB guy to manufacture the final boards anyway. So of course I will do a lot of testing with those. Likely I will have 2 machines running, one with a 40MHz OSC, and another with a 32MHz OSC. And see if the 40MHz one dies or not.
I am still investigating, this seems a bit of a mystery
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EDIT:
Checked bottom of the motherboard to the top of the booster CPU, all connections are fine. So there is nothing other than the CPU in circuit, direct connection as "normal" just doesn't work.
I took the CPU off the booster , back in the MB... works again.. So I will try a new CPU on the booster board.. This really doesn't make any sense...
EDIT2:
OK So I plugged the booster board directly ontop of the CPU in the MB socket.. now it doesn't boot.. hmmm.. there are no shorts on the board from what I can see.. even if there was, doesn't explain 10+ hours before it failed...
EDIT3:
OK so short on PCB between DTACK and BG , must have happened during my last re-solder.. So back on with the CPU again...and.. still doesn't work.. bizzare..
EDIT4:
Tried the suspect CPU in my old V1 booster (32mhz) and CPU came right on.. so can't be the CPU... all connections on the new booster board seem fine.. so what else is there ??
EDIT5:
Put a new CPU on the problem booster board and now it boots! So why does that one CPU work in the MB, work in the V1 booster, but died on the new booster boards.. Even though at the moment its hardwired for 8MHz.. No bad connections, no shorts, just refuse to work..
EDIT6:
So back to working at 40MHz now.. well bit unstable as not got the sil arrays in yet.. and its died again...
EDIT7:
Tried a previous revision board and hardwired that to 8mhz and seems to exhibit the same "fault".
I really think there is something bad on these test boards.. but I don't know what.. Will just have to wait until I get my proper boards and do more tests on those..
EDIT8:
So I found a short on the CPU
So now its running at 40MHz again (though with a different CPU than originally). Though it still doesn't explain why it died earlier when the CPU tested fine in another board.
Think I am just going to put this down to its solar eclipse & Friday 13th.. Good enough explanation as any other...