Fast forward a few months later... getting this beast up and running took a fair bit of love, money, and patience. But, YES WE DID!
This will do for now. After all, you are adding TWO SIDs for the price of... well, a fairly hefty FPGA price tag. But... STEREO BEECHUS!
The jailbars are next on the to do list. I ordered the C128 LumaFix, which should be coming here before 2020.
All in all, it was a good adventure in restoring a C128, my first and probably only one. I have a number of extra parts left over (need one repaired? I might be your Huckleberry). And I am thrilled with how this project turned out. Now I can turn my attention back to a non-working A2000 board belonging to a gentleman from my home state of FLA.
I was so happy when I finally saw this magical prompt. It was as if a thousand Atarians suddenly cried out... and then SILENCED!
In all seriousness, I wasted a lot of time chasing rabbits down the wrong hole and fighting figments. At first I considered the Super-PLA to be a primary culprit. Then the MMU. Spent hours buzzing out traces and poking at it with a logic probe. Then it appeared that the high RAM bank was problematic when I finally could get it to boot into 64 mode but not 128.
Ran the pocket scope I built from a kit a few years back and it gave me some reasons to think there was some logic IC issues. After replacing those I decided to go for broke on the high RAM. Finally went down to Office Depot for to laminate schematics so I could write on them. This helped me understand the data flow and the I/O a fair bit but didn't put me closer to a solution. I even consulted the wisest of wizards in the Pacific North West. Needless to say, I was getting flummoxed.
Oh, and did I mention that during some late night soldering sessions, I was cleaning my desoldering tool and the glass capture cylinder rolled of my workbench into a gagillion pieces? Well, that sucked because it seems I could only order replacement parts from POLAND. Nearly 5 weeks later the replacement part finally came in and I could get back to work. This gave me some time to think about the problem and it occurred to me that maybe I am looking for a complex answer when it is relatively simple: The machine boots to 64. The machine boots to 128 screen with no BASIC. Hmm.... BASIC.... Off to order more ICs from Ebay. Luckily, there's still some IC stock available of most of the custom ICs and not all of them cost an arm and a leg. One of them, the C128 BASIC ROM finally shows up and in it goes. And... we have a startup! All systems check out and, other than some very nasty jail bars, we're looking good to go.
Now, on to that missing SID chip! (and 8701 clock circuit). The clock circuit was easily solved by Mr. Eslapion's TOLB 8701 replacement-which worked perfectly with no fiddly. For a Canadian product, it didn't seem to mind the occasional bad "Eh?" jokes as I was installing. As in "Ya like that, eh? Feels a little snug, don-cha-know, eh?"
The FPGASID, on the other hand, was all business. Several jumper wires were the order of business, followed by some fiddly pin counting and corralling the excess wire. If this becomes it's permanent home, we'll look at some options for a more elegant wire configuration. For now, this will work fine.