I have the same motherboard and, to get it to POST, I had to replace the Dallas RTC (fortunately, I was able to secure a "new old stock" Dallas RTC that still worked fine).
This motherboard is very similar to the OPTI495 chipset-based range of "hybrid" motherboards that could also accept both 386 or 486 (5v) CPU's. However, most OPTI boards I've come across do not require a user to swop out either the crystal oscillator or resistors.

Regarding the BIOS ROM chip - it's perfectly fine for it to display "386DX" since it's (by default) a 386 motherboard that can upgrade to a 486 CPU. The BIOS ROM itself does support both 386 & 486 (5v) CPU's - if you dump the BIOS ROM contents with a utility like Navratil System Information (NSSI) and read the contents of the BIOS ROM (with an ASCII editor), then you'll see the list of CPU's supported.

No, you cannot flash this BIOS ROM chip (at least, not directly in the motherboard) - it is an EPROM chip and to reprogram it, you need to physically remove the chip, erase the contents in an EPROM UV eraser and then write the new contents to the chip with an E(E)PROM programmer. I wouldn't recommend this.
If you do find a more up to date BIOS ROM version, rather use a drop-in replacement EEPROM chip (like the W27C512).
Check out this link (and the downloads section): https://theretroweb.com/motherboards/s/fic-4386-vc-hd

You will definitely benefit by upgrading the CPU from a 386DX 40 MHz to a 486DX2 66 MHz which will the make for a great late 80's to early 90's DOS based system.
Just be aware that, once you go above a 486 DX 33 MHz, you will be slightly bottlenecked by the ISA bus (in terms of your graphics card throughput), particularly in games like Doom. Unfortunately, this motherboard does not have any VESA Local Bus slots that you can benefit from.

PS: If have some time, scan in the entire manual and share it with the community that houses the information on the Retroweb (there is a Vogons page as well where you can make contributions).

Thanks so much for the reply!

I will scan the manual next time I have the chance. Although Retroweb already has the manual but I believe mine is a newer revision from December '92.

I have never come across anything similar like switching resistors and swapping oscillators in order to upgrade a CPU that's why I wanted to make sure I interpreted it correctly (the manual only has the table, no description of the necessary steps). All my attempts at upgrading only started later with the T2P4 board.

I'm glad I don't need a new BIOS chip or an eeprom programmer, thanks for confirming.

Strange that yours didn't post with a drained battery alone. Here's my post screen:

I even got mine to boot by removing the HDD and booting from FDD. It wouldn't save the HDD parameters and without HDD Auto Detect no IDE HDD would ever work without a good battery. Even though the FDD defaulted to a 5.25 1.2 MB drive in BIOS I could use a 1.44MB 3.5 disc, it just wouldn't read past 1.2MB. Of course I had to do a bit of benchmarking (a bit strange that writing is faster and doesn't drop off like reading after the cache is exhausted)

I once had a 486 DX/2 66 with VLB but sold it sadly when I got a Pentium 166. But I believe for most DOS games the 486 should suffice even without VLB. It's more of a challenge to see what the board is capable of and not to make the fastest 486 (for that there's DX4s out there with PCI boards).

Siran wrote on 2023-05-24, 23:07:

I even got mine to boot by removing the HDD and booting from FDD. It wouldn't save the HDD parameters and without HDD Auto Detect no IDE HDD would ever work without a good battery. Even though the FDD defaulted to a 5.25 1.2 MB drive in BIOS I could use a 1.44MB 3.5 disc, it just wouldn't read past 1.2MB. Of course I had to do a bit of benchmarking (a bit strange that writing is faster and doesn't drop off like reading after the cache is exhausted)

Yes, what you've described are the symptoms I also experienced - it essentially rendered the PC useless until the battery was replaced.

Siran wrote on 2023-05-24, 23:07:

I once had a 486 DX/2 66 with VLB but sold it sadly when I got a Pentium 166. But I believe for most DOS games the 486 should suffice even without VLB. It's more of a challenge to see what the board is capable of and not to make the fastest 486 (for that there's DX4s out there with PCI boards).

Agreed - there are plenty of DOS games that don't require a VLB .

jesolo wrote on 2023-05-24, 21:24:

PS: If have some time, scan in the entire manual and share it with the community that houses the information on the Retroweb (there is a Vogons page as well where you can make contributions).

Done: https://theretroweb.com/motherboards/s/fic-43 … vc-hd#downloads - Rev. B scan by me.

Siran wrote on 2023-05-29, 12:48:

jesolo wrote on 2023-05-24, 21:24:

PS: If have some time, scan in the entire manual and share it with the community that houses the information on the Retroweb (there is a Vogons page as well where you can make contributions).

Done: https://theretroweb.com/motherboards/s/fic-43 … vc-hd#downloads - Rev. B scan by me.

Excellent - thank you

Just a quick heads-up if someone has the same board and wants to upgrade. A fellow retro fan swapped the Dallas IC with a Necroware battery-replacement and even upgraded the BIOS EPROM from the installed 1.10K to 1.15k (although the 1.10K should also support a 486 without a problem). After this I was ready to try the upgrade and I'm happy to report I could successfully install a 486DX2-66 on the 4386-VC-HD motherboard, disabling the onboard 386DX-40. I had tried last week but the PC wouldn't post. Did the same procedure once more yesterday - set jumpers, swapped the two resistors (to RN10 and to RN51), replaced the onboard 80MHz quartz oscillator with a 33MHz one, removed the iit 387c FPU that my father had installed 30 years ago and placed the 486 into the socket. Only this time I used more force and I could feel it sliding into place, which I didn't last time. Lo and behold, I was greeted with a glorious post screen

An AMD and Intel CPU together on the same board - could this be love?

Speedsys made a massive jump from 6.49 to 24.93, cache throughput also increased by 2MByte/s

Cache performance seems to be influenced by faster latencies - went down from 37.6ns/byte to 22.8ns/byte

All in all I'm very pleased with the upgrade, I even tinkered with the LED display on my case to show 33/66Mhz depending on turbo state which was an hour of trial and error thanks to all the jumpers, but I got it to work in the end.

Siran do you remember when you got your computer and how much was it? Im wondering where combo boards were price wise compared to 386 and 486 ones.

rasz_pl wrote on 2023-08-05, 17:11:

Siran do you remember when you got your computer and how much was it? Im wondering where combo boards were price wise compared to 386 and 486 ones.

It must have been in 1993, the manual I got with the motherboard is dated December 1992, so it must have been later. I believe it cost around 2.000 Deutsche Mark, so about 1.000 €. I'm not sure if the monitor was included though. I didn't even know (or didn't remember) that the motherboard had the option to upgrade to a 486DX2-66 until I found it some months ago in the attic, so it definitely wasn't part of my decision to buy it back then, I know it was one of the cheaper options at the time, which was one of the reasons we bought the PC. But I've been remembering more and more and my then best friend bought the same PC but later upgraded to a 486DX-33 but kept the case etc. so he must have already upgraded his with a better CPU back then. I didn't really give it much thought until a few days ago. Since I got an entirely new PC somewhere in 1994 (a 486DX2-66 with VLB) and gave the old PC my father I never really thought about it again until I found it in the attic.

Btw - if you're interested in prices, there's tons of old ads, especially for German retailers Vobis and Escom, on the Internet which might give you an idea. I guess it's safe to say that many 386 PCs, especially the ones with an AMD 386DX-40 (the 40Mhz would be a good indicator as Intel never sold a CPU with that speed) from around 1993 might have a combo board with an onboard Am386DX-40 like mine.