Without the regulator you can only use 5v cpu's. The dx4 is a 3,3v and could probably go defective at 5v!

Are you using normal Fastpage ram sticks? Those are weird looking ones you have there, are those server ram perhaps? Any beeps from a speaker?

Based on the error codes, I would say check your memory.
These earlier motherboards only supported Fast Page Mode (FPM) RAM - you can do a search on Google, based on the part numbers that are printed in the memory module, to determine the type of memory. .

Just make sure the memory is seated properly as well.
It's also possible that your memory might be defective.

And, yes. An Intel 486DX4 100 MHz is a 3.3V CPU. You cannot run it on this motherboard, unless you add a voltage regulator.

jesolo wrote:

Based on the error codes, I would say check your memory. These earlier motherboards only supported Fast Page Mode (FPM) RAM - yo […]
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Based on the error codes, I would say check your memory.
These earlier motherboards only supported Fast Page Mode (FPM) RAM - you can do a search on Google, based on the part numbers that are printed in the memory module, to determine the type of memory. .

Just make sure the memory is seated properly as well.
It's also possible that your memory might be defective.

And, yes. An Intel 486DX4 100 MHz is a 3.3V CPU. You cannot run it on this motherboard, unless you add a voltage regulator.

Thanks for your reply. I have 10 different types of SIMM with 14 in total (and one of them pulled from a working machine). Tried all of them in the first slot. All except two of them would give that error code as above. One of them would actually cause the system to beep continously, and both of them gave different error codes (even different ones when I tried the same module). Anyway, from that, I'm not too sure that's the problem, unless that slot is a problem. I tried inspecting it, but it's hard for me to see what I should be looking for.

I had also reseated all the chips on the board. Could it be one of the cache chips is fried? I have another board with the same chip, but a different timing, but I'm not too sure that I can use that one? W24257AK-20

meljor wrote:

Without the regulator you can only use 5v cpu's. The dx4 is a 3,3v and could probably go defective at 5v!

Are you using normal Fastpage ram sticks? Those are weird looking ones you have there, are those server ram perhaps? Any beeps from a speaker?

Yes, I am going with the assumption now that my DX4 might be dead, that's why I'm only trying 5V CPUs for now 😀

No beeps, except when no RAM is installed at all.

henrikwils wrote:

jesolo wrote:

Based on the error codes, I would say check your memory. These earlier motherboards only supported Fast Page Mode (FPM) RAM - yo […]
Show full quote

Based on the error codes, I would say check your memory.
These earlier motherboards only supported Fast Page Mode (FPM) RAM - you can do a search on Google, based on the part numbers that are printed in the memory module, to determine the type of memory. .

Just make sure the memory is seated properly as well.
It's also possible that your memory might be defective.

And, yes. An Intel 486DX4 100 MHz is a 3.3V CPU. You cannot run it on this motherboard, unless you add a voltage regulator.

Thanks for your reply. I have 10 different types of SIMM with 14 in total (and one of them pulled from a working machine). Tried all of them in the first slot. All except two of them would give that error code as above. One of them would actually cause the system to beep continously, and both of them gave different error codes (even different ones when I tried the same module). Anyway, from that, I'm not too sure that's the problem, unless that slot is a problem. I tried inspecting it, but it's hard for me to see what I should be looking for.

I had also reseated all the chips on the board. Could it be one of the cache chips is fried? I have another board with the same chip, but a different timing, but I'm not too sure that I can use that one? W24257AK-20

One thing that I've learned over the years (particularly when it comes to computers) is that just because something is working in machine A, doesn't mean it will necessarily work in machine B.

All the memory you have might be EDO memory (meant for Pentium 1 motherboards) - check what is printed on the RAM chips and perform a Google search to determine if you have FPM or EDO RAM.

Another possibility, although unlikely, is that your BIOS ROM became corrupted - this can be rectified by burning another ROM chip with your system BIOS.

jesolo wrote:

All the memory you have might be EDO memory (meant for Pentium 1 motherboards) - check what is printed on the RAM chips and perform a Google search to determine if you have FPM or EDO RAM.

I didn't throw away memory sticks. As I said, this HAS been booting up. Upon inspection, only a few of my memory sticks are EDO.

I've flashed to the newest BIOS (from Phil's website), removed all cache chips, removed display adapter, AND I've tried another CPU, that I know is working, and I still get C5 C1 on the PC analyzer.

Anything else to check?

Carefully check all the contacts in the SIMM slots, i've seen boards where some of them lost their "springiness" or were bent. These can usually be corrected with a small flat screwdriver or the tip of a cutter blade. Also inspect the pcb tracks leaving from the slots, check for scratches, cuts, shorts...

quicknick wrote:

Carefully check all the contacts in the SIMM slots, i've seen boards where some of them lost their "springiness" or were bent. These can usually be corrected with a small flat screwdriver or the tip of a cutter blade. Also inspect the pcb tracks leaving from the slots, check for scratches, cuts, shorts...

I already checked the board. It looks really clean..

The springs on the memory slots does look like they could use a tiny bit more "springiness", so i used a needle to bend them slightly outwards. Still no difference. I've also tried using a bit of force to ensure the DIMM was properly seated while booting, as one of the edge springs is almost useless.

I have found the problem - at least physical faults that will be a problem. Between the SIMM and CPU socket, right in the middle of SIMM3 and SIMM4, 3 traces are blown, as well as an SMD, and another SMD seems to have burnt away in the lower left corner of the CPU socket.

So I need to get the board repaired, and if that works, hopefully I can retrofit a voltage regulator and perhaps (if not too much work) add the VLB slots as well. I got an identical board (same revision), so I should be able to match the components.

I had the same problem with a 486 board I was using. It only ran at 5v even though it did have jumper settings for 3v too.
So I could only use a
486dx-33
486dx2-50
486dx2-60
https://en.wikipedia.org/wiki/Intel_80486

And it only accepted FPM ram.

Once I got that straighten out it ran fine.