Okay so I'm learning about scopes here but not still not enough to actually use one. Meanwhile, I'm doing the tried and true 'chip swap' method and just messing around with the logic probe to see what I can learn about this KIM-1 I have.
To recap, there is nothing on the display when I hit reset. There *was* a broken 556, that was replaced and we can see the reset signal all over the board including the CPU. I also checked out the 74145s and confirmed the LEDs do work (by shorting specific pins). So not that. I removed and checked the CPU in an Apple II I have -- works perfectly.
I'm wondering to what degree RAM can impact things. Would bad RAM knock out the display entirely? I've looked at the RAM with my logic probe, and every RAM chip after reset has the same pins high and low. I don't know enough to know if that tells us anything, but I would have thought there'd be some differences somewhere (?).
Anyway, I've mastered careful desoldering now so I'll just check them out quickly.. easy enough.
Obviously if one of the RRIOTs are gone I'm dead in the water. I do actually have a spare 6530-003 but not the -002 and I think that's the critical one.
Anyway, if anyone has any other suggestions pending my learning how to use a scope.. I'm all ears. And don't try to give me scope instructions just yet.. this is *way* over my head right now. :)
To recap, there is nothing on the display when I hit reset. There *was* a broken 556, that was replaced and we can see the reset signal all over the board including the CPU. I also checked out the 74145s and confirmed the LEDs do work (by shorting specific pins). So not that. I removed and checked the CPU in an Apple II I have -- works perfectly.
I'm wondering to what degree RAM can impact things. Would bad RAM knock out the display entirely? I've looked at the RAM with my logic probe, and every RAM chip after reset has the same pins high and low. I don't know enough to know if that tells us anything, but I would have thought there'd be some differences somewhere (?).
Anyway, I've mastered careful desoldering now so I'll just check them out quickly.. easy enough.
Obviously if one of the RRIOTs are gone I'm dead in the water. I do actually have a spare 6530-003 but not the -002 and I think that's the critical one.
Anyway, if anyone has any other suggestions pending my learning how to use a scope.. I'm all ears. And don't try to give me scope instructions just yet.. this is *way* over my head right now. :)