Update…
It was the RAM module. After thinking about it after Fugu’s email the other day it occurred to me I had done a capture of the standard RAM bank select lines (and I happened to dave it) and after looking at it again it looked fine. This evening I pulled the standard RAM module out, split apart a 30 pin DIP socket to make two 15 pin SIPs and plugged in of the option RAMs. AND…nothing. Sigh… Then I noticed I had not plugged the ROM back in after cleaning the flux from the board. So, the ROM was installed, and STRL-BRK done on power up and…It’s ALIVE! Bwa-ha-ha-ha! It’s ALIVE! I tried reflowing the original standard RAM module and it still did not work. I could ohm out each line to each individual RAM chip and maybe get lucky and find one open trace, but I would guess that a bad RAM chip is more likely. I’ll look into making some more RAM module or buying a few, for now I have 16K. As luck would have it the second M100 I bought from across the state arrived yesterday, I still have not opened it yet. It is supposed to work, got it from the original owner who seemed like a nice guy. A grand total of $61 including shipping. Now I’ll put together an order for enough caps to finish recapping the first M100 and re-cap the 2nd one while I’m at it. I also need to try and calculate a super-cap size that will at least match the original NiCad battery. Thanks again everyone (especially Fugu) for your help. Jeff From: M100 <[email protected]> On Behalf Of Fugu ME100 Sent: Thursday, May 10, 2018 10:06 AM To: [email protected] Subject: Re: [M100] SPAM-LOW: Re: New member - question on 'half' alive Model 100 The address could be stuck internally on the RAM so the address line would appear OK externally. The fact the ROM runs correctly with the shared Address line would indicate the address lines are generally OK. It could be floating on the module as you suggest, look to see if there is any corrosion on the module and the pins to the module are in good condition. Perhaps try reflowing each of the module pins to make sure there are no dry joints? I am currently looking into producing some sort of test harness for the model T however the lack of socket for the 8085 makes it hard to add in a test fixture. Even trying to tri-state the 8085 appears difficult as it does not tri-state the ALE, all the other lines are OK. Another option would be to try and monitor what it does with something that plugs into the RAM socket. That way at least there would be a trace showing the bus activity. Being able to single step the 8085 might be another option with a known ROM in the socket.
