You can't use a 50MHz clock. That's for a DX 50 MHZ. For a 33/66 MHz cpu you need a 33MHz quartz.
I don't think you can disable all cache by jumpers in that board, but i could be wrong. I have a similar one and the lowest cache setting is 32KB.

Following links for 486-VC-HD gave me a PDF for 486-VC. FWIW, it says "Supports 0KB/64KB/128KB/256KB of direct mapped write-back cache memory." then doesn't give jumpers for using 0kb...

Also a handwritten note on the CPU Clock jumper section that I can't make sense of. Maybe you want to have a look,
http://www.elhvb.com/supportbios.info/archive … vc-hd/486VC.PDF

EDIT: have a look at this thread. Unfortunately Google's translation is refusing to work with my browsers, but it looks like the same topic.
http://www.dosforum.de/viewtopic.php?f=1&t=8886

sprcorreia wrote:

You can't use a 50MHz clock. That's for a DX 50 MHZ. For a 33/66 MHz cpu you need a 33MHz quartz.
I don't think you can disable all cache by jumpers in that board, but i could be wrong. I have a similar one and the lowest cache setting is 32KB.

I think the board clock is oscillator/2, so it shoud run at 33 MHz, at least in it's current state.

pewpewpew wrote:

Following links for 486-VC-HD gave me a PDF for 486-VC. FWIW, it says "Supports 0KB/64KB/128KB/256KB of direct mapped write-back […]
Show full quote

Following links for 486-VC-HD gave me a PDF for 486-VC. FWIW, it says "Supports 0KB/64KB/128KB/256KB of direct mapped write-back cache memory." then doesn't give jumpers for using 0kb...

Also a handwritten note on the CPU Clock jumper section that I can't make sense of. Maybe you want to have a look,
http://www.elhvb.com/supportbios.info/archive … vc-hd/486VC.PDF

EDIT: have a look at this thread. Unfortunately Google's translation is refusing to work with my browsers, but it looks like the same topic.
http://www.dosforum.de/viewtopic.php?f=1&t=8886

First link points to a differnt revision.

I happen to speak German and can read the second link, They mostly talk about changing the quartz.

I'll check with mine tomorrow. It's not the same model, but it's a 4386-VC-V.

Awesome, thanks! That's the one with the integrated 386, right?

What could be the problem? Jumper settings? Lacking controller card? Or something else?

Here is the manual:
http://motherboards.mbarron.net/models/486isa/486vchd.htm

Controller card isn't needed for POST. I'd try putting VGA card in another slot.

I see you have PC speaker connected, does it make any beeping sound?

Do you think the board worked before? I usually remove cache chips only from the boards that are confirmed dead.

The manual is for a different/newer version, different layout and all that.

Already tried the VGA in another slot, nothing.

No beeps.

I think the board is brand new, no signs of usage, no dust at all. That'd explain the lacking cache chips (even so, 486s without cache are far from unheard of).

According to the manual, it does support 0KB of cache, but no jumper setting is shown.

Should I try it without CPU/RAM, to see if it beeps?

Without CPU there won't be any beeps. You can try without memory.

Even if it looks like new, it isn't. It is around 20 years old and anything can happen. I have several "looks like new" boards that are dead or at least I can't find what is wrong. I thought of buying those diagnostics cards that you plug into ISA slot and it displays where the error is. Maybe someone has some experience with them?

kixs wrote:

I thought of buying those diagnostics cards that you plug into ISA slot and it displays where the error is. Maybe someone has some experience with them?

I do. They're a great diagnostic aid, for the price they really pay for themselves after helping you get just one board up and running. Just don't expect them to be some sort of magical computer repairing fairy, treat them more like a multimeter, by itself it won't do you any good, but with a bit of knowledge and analytical thinking you'll wonder how you managed to work without one.

They usually come with a small booklet explaining what most codes mean for various BIOS manufacturers, but for me it has been useless most of the time. Only once it pointed me to the cause of the problem (loose keyboard controller chip), in reality don't expect the code you're getting to make sense, it's more about knowing how things behave and what you can infer from certain symptoms.

The great thing is that you can assess core functionality with only a working CPU and BIOS chip, no need for RAM, video or other stuff to get POST codes and that helps you eliminate a lot of variables. Experiment on all kinds of good & bad motherboards and you'll quickly get a hang of how things work. In my case the card has helped me diagnose the following:

• Missing supply voltages (bad PSU, burnt fuses or traces)
• Stuck reset signal (shorted case lead, motherboard short to the chassis, bad device or bad PSU holding the board in reset)
• Bad device (RAM or exp. card) causing reboot loop early in POST before beeps & video
• Bad device causing POST to freeze early
• Bad VRM not supplying power to CPU (no POST codes)
• Burnt CPU (no POST codes)

Sometimes a particular ISA/PCI slot won't give POST codes so if you don't get any, try others first. As you can see it's not indispensable (many of the above problems can be diagnosed with simple component substitution) but it does help immensely with the 'invisible' issues. If you like to tinker with hardware, definitely get one.

Checked my motherboard with the dx-2 66 and the oscillator is 33.33MHz.

OK, thank you! I assume yours is running? Could you test if it runs if you leave the cache jumpers off?

*bump*

So I got a second one that IS working. Did the RTC battery mod, works. Still having trouble getting a hard disk recognized, but it's looking good. Oh, and the BIOS apparently doesn't have the 504 MB limitation, so that's good.

It's entirely possible that the first one wouldn't start because of the 50MHz oscillator and the installed DX-33. So I need to either get the right oscillator or a DX-50. A working DX-50 system would be awesome 😁

In short, sprcorreia was right all along.

If the 2nd motherboard has socketed oscillator, then just move it to the other board to test it.

Funny, I assumed it was soldered on, but on the first pic it looks socketed - will check when I get home. Thanks for noticing!

Anyway, I have put in offers on a DX2/66 and a DX50 on ebay. This really has the potential for building two awesome early high-end 486 systems (before VLB, that is).

I have some DX-33 chips and they seem to work @50MHz just fine.

oerk wrote:

[...]This really has the potential for building two awesome early high-end 486 systems (before VLB, that is).

One can't build an awesome highend early 486 around a VIA based 486 board 🤣
While it is good for a stable system, the chipset has a bad memory performance, hardly covered by the installed cache. It really is a slow thing.
If you want to build an awesome pre VLB 486 system I would prefer some pacy UMC or SiS based board with ISA-only layout. There are many around. Or go the EISA route. It is also a pre VLB technology and there are some really fast (SiS based) boards available.

Ahhh, then there's really no point in upgrading to a DX50 or DX2/66. Embrace the slowness! 🤣

Well, I still have the PS/1000 with the sound card problem. Don't have much hope for it though. I should get around to sending you the boards to test (if you still want to).

Sooo, update time!

The working board wouldn't POST with the 50MHz oscillator either. I couldn't be bothered to test the non-working one with 33MHz because swapping CPU, cache, RAM and ISA cards over is a pain and I was too impatient because I wanted to finally build a working system.

So this is what I did over the weekend... took the unimpressive Batman/Pentium 60 board out of the AT case, put it up on ebay, and built a working 486.

Bad pictures ahead:

Still need to do some cable management, wanted to make sure everything works first:

Specs:
- FIC 486-VC-HD
- i486 DX-33 (maybe swap a DX2/66 in, maybe not)
- 256KB L2
- 32MB RAM (insane, I know - I'm contemplating taking half of it out because it's not necessary at all)
- Generic Multi-I/O controller
- Trident 8900 something with 1MB (maybe swap it out at some point for something better, doesn't have to be ET4000, Cirrus Logic would be nice)
- Realtek RTL8019AS nic - that's the last problem left, haven't got it working yet
- Soundblaster 16 CT2940 with OPL3 - so far I'm really impressed with that one! Very low noise even with PC speaker connected, great sounding OPL3. Not at all like my AWE32 CT3980 that's noisy as hell and has muffled sounding OPL3.
- 3.5" and 5.25" floppies, both working perfectly
- 1.2 GB Quantum hard drive - had to use Ontrack Drive Overlay
- 2 GB CF card
- Teac 32-speed CD-ROM - yeah, I know - but these are A LOT more reliable than early CD-ROM drives and read CD-Rs without problems too
- MS-DOS 6.22 / WfW 3.11

Modded the useless Eco button on the case - swapped the momentary push-button out for a switch, so now it's a working turbo button!

I'm also considering making the speaker switchable, i.e. adding a switch which routes the PC speaker signal either to the internal speaker, the SB16, or off. Easy to do and practical (real retro feeling with internal speaker, option for using headphones for late-night gaming).

FGB was right. Memory speed is SLOW - <10MB/sec on RAM, L2 is two times faster at best.

But I enjoy the system as it is. It just feels right - as long as I don't play anything newer than 1993 (that isn't an adventure) on it.

Currently playing through Sam & Max.