Fubar At first, only the 48V LED was on. After I replaced the regulator, the 6V LED came on. The voltages looked smooth on my scopemeter.
The yellow LED indicating that the CPU is at least limping is out.
As I mentioned, the two diodes that drive the input of the 3.3V regulator burned up . The one diode driven by the 6V rail burned up when I put the board in the game after replacing the 6V regulator. When that happened, there was some smoke and some coils were enabled/locked on. I shut the game off immediately.
I moved to the bench (I should have frigging verified everything on the bench at first ... my damn arrogance led me to believe that the problem was fixed and that the game would fire right up ... that's the last time I try and impress my son ... makes me feel like an ass since I have a frigging nice power supply to debug this stuff ... idiot!).
I powered up the VPROG node with 6V driven by an external supply. This burned up the other diode that is connected to the input of the 3.3V regulator.
I also removed the 3.3V regulator ... still a dead short on the 3.3V rail. I had pulled a couple of caps off the 3.3V rail hoping one of them may have shorted ... that appears to not be the case. I am reading about 2 Ohms from 3.3V to ground.
There aren't many other components on the 3.3V rail ... there are some passives, the CPU obviously, a logic gate, and the TX optocoupler IIRC ... I guess I could pull everything else and see what happens. Given where I am at with the board, I was going to put an external 3.3V source on the 3.3V rail on the board and hope to see something smoke a little to give me a hint, but I also don't want to risk burning up any pads on the PCB (these PCBs are *cheap* ... I mean they are just above trash level ... its disgusting that they charge $9K+ for machines now using such shitty PCBs ... I'd expect better in commercial equipment, but I digress ... you cannot so much as go a few degrees over the melting point of solder or else you risk losing pads ... fortunately, I only lost one, and it is really easy to work around it).
This is frigging ridiculous that Stern won't provide some basic firmware that would allow one to flash the board themselves and allow the game to update it to the appropriate version. The cheapest I've found this particular board is $400 (I refuse to pay that ... I can wait) ... they were able to be had for $130 from some places, but they're sold out everywhere. It seems that the coil driver transistors and the gate driver ICs they use are unobtanium right now (they have a 46 week lead time at Mouser and Digikey).
From what I understand, Stern uses these same node boards in toppers ... that's probably why they want their code encrypted. If they don't, there'd be a million "interactive topper" options out there. I wish they'd just make a damn encrypted node board for that crap and leave the ones that are required to play the damn thing unencrypted.
Are you positive that the firmware is encrypted? I've seen people speculate that it is, but your post is the first time I've seen someone confirm it. If it is encrypted, that means that it's worthless to probe the bus and try and capture it.