h-a-l-9000 wrote:

Damaged SIMM: The pins on the outer side are redundant (5V) - it may work despite the pin missing.
For the keyboard: There should be a 74*07 logic chip near the connectors. The connector in question will lead there. These are the two data lines. 5V and GND will be easy to find.

No luck finding a 74*07 chip.

High-res photographs here:

http://imgur.com/a/dJjEr

Is that "MEGATRENDS" chip a keyboard controller i wonder? It says MEGA-KB in the part number, so I bet it is.

Yes, the PLCC-44 chip is the keyboard controller. If they have kept the pinout then KBD CLK (TEST0) should be on pin 2, KBD DATA (TEST1) on pin 43. A reference schematic of the PC AT is attached.
The 74ALS05 is very similar to 74*07, and very close too. Also the 10k resistors are present.

@BloodyCactus: I rather assume your board has some internal RAM than believing it can run a 32-bit CPU on 16-bit RAM.

h-a-l-9000 wrote:

@BloodyCactus: I rather assume your board has some internal RAM than believing it can run a 32-bit CPU on 16-bit RAM.

I assume it's possible at some level since there was a Make-It 486, right? That used a 286's 16-bit memory bus for 486 operations?

http://i.imgur.com/sVgjWx9.jpg

Boots up just fine with 4x256kb chips. Now to figure out which is the PC speaker and which is the keyboard connector...

The port I suspected to be the keyboard connector was, in fact, the keyboard connector. I have a booting, usable system now...

I'm having a hard time tracking down the pc speaker port, though.

By process of elimination, I don't believe that P1 is speaker because it's got a jumper attached; why would speaker have a jumper?

P5 (2 pin) and P10 (keyed 4-pin) are illustrated in one of the photos I found as having a single connected wire, so I don't believe those are correct. A pc speaker should have a special speaker positive/speaker negative connection.

That leaves P2 (keyed 5-pin) and P12 (4-pin).

I'm GUESSING that P12 is the most likely connector for PC speaker...

I suspect I need an oscilliscope to test output for pc speaker?

I guess I'll check for voltage on P12; if there's nothing there during normal operation I think that might be it...

Well that was probably not a good guess.

I measured the voltages and ground of each lead:

P1: 0v 0v GND - Speaker?
P12: +5v +3.9v +3.9v 5v ???
P10: +5v GND LED?
P2: +5v NC GND +5v GND LEDs?
P5: +3.9v NC GND +5v ???

Speaker shouldn't have any + voltage when there's no active been, right?

I'm also curious as to what that extra socket is for. The 486 already has an FPU in it. Maybe it's for a 486SX + FPU?

My guess is weitek processor?

It seems larger than the 486 socket.

In any event, it's working great with some old games I've been playing...

Hello, this is my first time posting. I just bought one of these exact boards on Ebay, and with it ariveing in 2 days, I was wondering if you had found any documentation on it? It doesn't have any of the ram slots populated and since I dont have it yet, I don't know how many MB of ram it can take.

Here is the Ebay listing:
https://www.ebay.com/itm/275177709984?mkcid=1 … emis&media=COPY

UPDATE:
I found documentation!

The SBC I got was still in its original bag, and the bag had a hidden sticker labeing it as a SB486T2C/66!
A quick Google later and here is the User manual on The Retro Web!

https://theretroweb.com/motherboards/s/ics-computers-c4dx

Image from The Retro Web: