Thats usually not a Dual Board, it is 386 or 486.
About the memory:
Soldering might not be enough as you have o tell the chipset to use the PS/2 banks instead of the old SIMMs. So it is probably still expecting old SIMMs.
Then the older SIMMs use Parity. I am not sure if those very early PS/2 memory supporting boards also like to have parity and maybe even a memory presence detect encoding. Then you should check that you use no EDO.

Also check once more if it really supports 3.3 V CPUs.
And I think it is a FPU socket and not for 386DX.

This could be a candidate:
http://artofhacking.com/th99/m/U-Z/30994.htm

http://artofhacking.com/th99/m/I-L/30548.htm

http://artofhacking.com/th99/m/C-D/30529.htm

http://artofhacking.com/th99/m/C-D/30726.htm

I can't get the above links to load for some reason, so this may be redundant, but it appears this is your board.

That other socket is not for a 386. It's for a Weitek 4167 coprocessor. It's a mostly useless feature that was only found on fairly early 486 boards. Just to be completely clear, DO NOT try to put a 386 in there.

I highly doubt that board supports write-back cache, since it predates any of the CPUs that supported it. So don't waste your time swapping out chips just for that. You should be able run a DX4 (and perhaps even a 5x86) in it, though remember it's a 5V-only board, so you shouldn't plug a regular 3.3V chip directly into it. You'd either need one of the socket adapters with its own voltage regulator, or one of the special Intel DX4 'Overdrive' chips which can be run directly from 5v.

As for the memory, the documentation only shows the 72-pin slots being used when the first two banks of memory are already filled, and there doesn't seem to be any jumper for switching between the types of memory, so it might be that you simply can't use 72-pin SIMMs by themselves... you may actually need to get some 30-pin SIMMs.

Old Thrashbarg wrote:

That other socket is not for a 386. It's for a Weitek 4167 coprocessor. It's a mostly useless feature that was only found on fairly early 486 boards. Just to be completely clear, DO NOT try to put a 386 in there.

Well thanks for letting me know. It really looks like a 386DX could fit in the socket, but now I know not to do that (not that I have a 386DX on hand, anyways).

Old Thrashbarg wrote:

I highly doubt that board supports write-back cache, since it predates any of the CPUs that supported it. So don't waste your time swapping out chips just for that.

So then, the L1 cache on both chips would just be write-through?

Old Thrashbarg wrote:

You should be able run a DX4 (and perhaps even a 5x86) in it, though remember it's a 5V-only board, so you shouldn't plug a regular 3.3V chip directly into it. You'd either need one of the socket adapters with its own voltage regulator, or one of the special Intel DX4 'Overdrive' chips which can be run directly from 5v.

Does the 486DX2 run at 5V? The 486DX2 on the motherboard (it was already on the board, by the way) doesn't seem to complain at all. The motherboard itself, though, keeps beeping the PC speaker 3 times in sequence as I said earlier.

Old Thrashbarg wrote:

As for the memory, the documentation only shows the 72-pin slots being used when the first two banks of memory are already filled, and there doesn't seem to be any jumper for switching between the types of memory, so it might be that you simply can't use 72-pin SIMMs by themselves... you may actually need to get some 30-pin SIMMs.

Well, s***. The only 30-pin SIMMs I have on hand are two 2MB sticks, and to my knowledge, that's a non-standard size which I'm not sure this motherboard will take. I'll have to look around for some 30-pin SIMMs, enough to make 16MB of RAM (that's what I'm aiming for in my 486 build).

95% of 30 pin simms come in the following sizes:
256k , 1mb, 4mb, 16mb

Most boards wont take 16mb 30 pin simms. Usually only the workstation high-end boards would. Yuor best bet is finding 8 4mb simms. I would search ebay for "4mb 30 pin simm" Look for someone selling a lot of 8 or similar.

Well, sure enough, the motherboard first checks for RAM at the 30-pin SIMM slots. I took 4 1MB SIMM sticks out of a 386SX-based computer just to test the motherboard, and the motherboard works. The 486 build I waited for can now proceed. So I'm gonna go over the checklist of things I have and don't have.

Have:

-Intel 486DX2 66MHz CPU (I may change this for an AMD 486DX4 100MHz if I can find or build a voltage regulator for the 486DX4)
-Motherboard
-ATI Mach 32 ISA graphics card
-ISA IDE controller card
-OPTi 82C929A sound card (not putting a SoundBlaster in this; I have a SoundBlaster Pro 2.0 CT1600 in my main DOS rig which is what I'll use if I want authentic sound)

Don't have:

-Compact Flash to IDE converter (I've got one on the way)
-512MB Compact Flash card (someone recommend a good one for me)
-4MB 30-pin SIMMs (I need 4 of these as I will not settle for less than 16MB of RAM)
-Low-speed CD-ROM drive (no faster than 12X)

Be careful with the AMD 486DX4 chips. Some of them are writeback only, some of them are write through only, and I think the last ones made supported both (basically being a relabled 5x86). The chips that only work in writeback mode probably won't work in your board even with a VRM. Intel DX4s are the same way. The ones with &E are write through only, and &EW is write back only.

The Motherboard is a BEK-4801/486WB
This motherboard has no CPU type configuration jumper meaning you have used what on it.
AMD 486DX4 supported motherboard had a carp load of jumper use lee there only in VLB and PCI forum