Here is a better photo of the cache controller (in the center under the CPU).

Note that the microhouse diagram shows the CPU in that location, and they both seem to be 132 pin PGAs...

Thanks, I'm just wondering about the location of pin 1; so I plug it in the correct way.

RetroViator wrote on Yesterday, 02:17:

Thanks, I'm just wondering about the location of pin 1; so I plug it in the correct way.

Noting that the board calls where you have the 386 U385 and where you have the 385 U386 we think you have them swapped...
You can use a multimeter to double check the pinouts, checking continuity of the corners to Vcc or Vss (or neither), and also verify which is for the 386 and which is the 385.
385 https://theretroweb.com/chip/documentation/do … b2659539195.pdf page 54, note Vcc is in one corner, Vss is in one corner, and pin 1 is diagonally across from Vss.
386 https://bg-electronics.de/datenblaetter/Schal … A80386DX-20.pdf page 5, note Vcc is in two corners, Vss is in one corner, and pin 1 is diagonally across from Vss.

Yes!

I wasn't thinking far enough out of the box. You're right, and that's why the 82385 socket was not tracing back correctly to VCC and VSS. I had looked at the Microhouse drawing several times, but not noticed that the CPU was next to the FPU, or if I did, I discounted it as an error. So, the orientation was correct, but the processor goes in U386 and the cache controller in U385. After this change, when I powered it up, I saw some heat on the CPU, but the system didn't post. I had replacement ICs for both the CPU and cache controller, and after putting them in, I see a bit more heat off both, but the system still isn't beeping or displaying video.

Thank you for helping me with this step of the puzzle!

Beyond reseating the BIOS chips and KBC, you'll want a POST code card next.

Great point. After reseating and applying Deoxit to both BIOS chips and the Keyboard BIOS, along with one PAL in a socket, I put in the post analyzer card.

It showed good power rails, I watch reset clear, and the clock light and the frame light stay lit. It freezes after POST code 04. TheRetroWeb says it's an AMI BIOS. I was able to confirm that the original CPU is dead, but I get the same post codes with either 80385 installed.

Turns out I had a RAM issue. I installed 4 1MB Parity SIMMs and I got to POST code 36 00. I also get two beeps--so that's good. I'm still not getting video, but I'm making progress!

The system is now booting! I fiddled with RAM so more and worked with the ISA slot for the video card and it is now looking good. I don't have a keyboard connected because it has an odd four-pin connector that runs to an off-board AT keyboard connection, which I'll have to make, but I should be good now. Thanks again @jakethompson1!

Nice.
I once had a System 310. It had Phoenix BIOS, and it was one of those where you hit Ctrl-Alt-Enter or Ctrl-Alt-Esc or such to get into SETUP only after DOS is booting (rather than before like a typical BIOS).

In hindsight this was pretty obvious; U386 for the 80386 CPU and U385 for the 82385. The socket numbers apply to the chips, the board does not have 380+ semiconductor sockets...

Yep. That struck me as obvious when I knew what I was looking at. 😄