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First post, by NScaleTransitModels

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I finally managed to obtain such a motherboard, so I could try my luck at a 486DLC + VLB build.
It's a UTD 4700 ALL IN ONE, made by Up-To-Date Technologies (never heard of them): https://stason.org/TULARC/pc/motherboards/C/C … ALL-IN-ONE.html
It came with a 486DX2-66, which booted flawlessly. However, as soon as I installed a 486DLC and switched it into 386 mode, that's where the problems began.
First, it would get stuck on the "WAIT" boot screen. I had to disable "auto WS and bus clock set" and add a cache wait state.
It was still not stable enough to fully boot from floppy, so I had to disable the Fast Gate A20 Option (not sure what this does).
After that, I was able to install Windows 95, and run games + benchmarks. However, I ran into more issues when trying to install NT 4.0 (as a stability test). It would be unable to copy files at random, and always lock up before completing the last graphical phase. It was not truly stable.

A memtest revealed countless errors within seconds (should've done this first, guess my excitement got the better of me). I tried tweaking several more BIOS/jumper settings, swapping stuff out, but the only way I could get the errors to go away was to switch back into 486 mode. Then even a DX2-66 @ 80 gives no errors.

Here's what I tried to no avail...
Swapping out:
-486DLC vs. 386DX
-Memory sticks (4x4mb 60ns, tested fine on a different machine)
-S3 P86c805 VLB video card vs. Mach32 VLB and various ISA cards
-ISA Multi I/O card, disabling on-board IDE and floppy

BIOS settings:
-System Boot Up CPU Speed high/low
-External Cache enable/disable
-Internal Cache enable/disable
-Fast Gate A20 Option enable/disable
-auto WS and bus clock set disable
-Dram Read/Write Wait State, AT Bus Clock Selection, Cache Read/Write Hit WS, Burst Cycle WS— safest timings and basically all combinations

jumper settings:
-VLB speed <= 33MHz, 40MHZ
-CPU speed 33 mhz, 40 mhz
-CPU type: 80386DX, CX486DLC (just marked as CYRIX on silkscreen)
-limiting cache to 128k

In conclusion, the motherboard works great when I plug in a 486, but as soon as I switch it over to 386 mode, it becomes unstable. Did I miss any BIOS or jumper settings that might make a difference? Maybe a cap went bad? Any input would be greatly appreciated.

PS. 486DLC + S3 VLB benchmarks from when it was stable enough to boot into Win95:
-3DBench = 25.0
-Doom = 11.656 FPS

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Builds:

  • PCChips M321; 386DX-25@40; PVGA1A, ISA 512kb
  • Acer VI9; 486DLC-40; Mach32, VLB 2mb
  • Chicony CH-471A; CX486s-40; Mach32, VLB 2mb
  • Gateway 2000 P5-60; Pentium-60@66; S3 928, PCI 3mb
  • DTK PKM-0033S; AM5x86-133@160

Reply 2 of 17, by NScaleTransitModels

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rmay635703 wrote on 2022-06-29, 18:31:

I’m guessing memory timing or a bad chip

Have you tried an actual 386dx ?

Yes, I tried a 386DX, a different 486DLC, and the jumper settings for 80386DX vs. CX486DLC. None of it made a difference.
I also tried all combinations of memory/cache settings, from 0-3 wait states. And multiple sets of 4x4mb 60ns modules.

Builds:

  • PCChips M321; 386DX-25@40; PVGA1A, ISA 512kb
  • Acer VI9; 486DLC-40; Mach32, VLB 2mb
  • Chicony CH-471A; CX486s-40; Mach32, VLB 2mb
  • Gateway 2000 P5-60; Pentium-60@66; S3 928, PCI 3mb
  • DTK PKM-0033S; AM5x86-133@160

Reply 3 of 17, by Jed118

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I too gave up on that dream - I had an EISA VLB 486/386 board, worked perfectly with the 486, would not take any form of 386 no matter what. At least you've got a manual for yours. I now have an IBM PS 1000 with a Blue Lightning chip in it 😁

My BIOS had (under advanced options) a "Enable 386" mode (or it may have said DLC too) - look around in there perhaps.

Youtube channel- The Kombinator
What's for sale? my eBay!

Reply 4 of 17, by NScaleTransitModels

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Jed118 wrote on 2022-06-29, 18:58:

I too gave up on that dream - I had an EISA VLB 486/386 board, worked perfectly with the 486, would not take any form of 386 no matter what. At least you've got a manual for yours. I now have an IBM PS 1000 with a Blue Lightning chip in it 😁

My BIOS had (under advanced options) a "Enable 386" mode (or it may have said DLC too) - look around in there perhaps.

Man, sorry to hear. Seems some builds just aren't meant to be. When it comes to 386/486 VLB boards, I've already missed/lost several auctions, even had other buyers beat me to buy-it-nows.
Nice PS/1000, I watched your video on it just now.

No sign of "Enable 386" in the BIOS unfortunately. Perhaps it's a hidden option... if anyone on here has a ROM programmer, I could maybe send you the board to play with.

Builds:

  • PCChips M321; 386DX-25@40; PVGA1A, ISA 512kb
  • Acer VI9; 486DLC-40; Mach32, VLB 2mb
  • Chicony CH-471A; CX486s-40; Mach32, VLB 2mb
  • Gateway 2000 P5-60; Pentium-60@66; S3 928, PCI 3mb
  • DTK PKM-0033S; AM5x86-133@160

Reply 5 of 17, by maxtherabbit

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I'd like to kindly direct you to the listing for your board on The Ultimate Retro

https://www.ultimateretro.net/en/motherboards/1383

Please stop linking to stason. UR is a community project run by guys from this very forum

Reply 6 of 17, by jakethompson1

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AT bus clock CLK2IN/6 is too fast I believe. CLK2 would be 66 or 80 MHz for a 33 or 66 MHz 386, so 11 or 13 1/3 MHz. You want CLK2IN/8 or CLK2IN/10 if you have those...
A 486 doesn't use the double-speed clock which might make a difference...

Reply 8 of 17, by NScaleTransitModels

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CLK2IN/8 is the lowest it goes. I tried CLK2IN/4 and /8, but it makes no difference. With either setting I can boot to Win95 and the sound card works (but memtest fails), so maybe they meant CLKIN instead of CLK2IN.

I tried both 128K and 256K jumpers, and enabling/disabling the cache in BIOS. Still failing memtest.
One option I haven't tried is Non-Cache Size Block and Non-Cache Address Block 1 and 2. The settings are 64kb, 128kb... up to 8192kb. Anyone know what this does?

Builds:

  • PCChips M321; 386DX-25@40; PVGA1A, ISA 512kb
  • Acer VI9; 486DLC-40; Mach32, VLB 2mb
  • Chicony CH-471A; CX486s-40; Mach32, VLB 2mb
  • Gateway 2000 P5-60; Pentium-60@66; S3 928, PCI 3mb
  • DTK PKM-0033S; AM5x86-133@160

Reply 10 of 17, by rmay635703

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Xeen wrote on 2022-07-23, 10:14:

I always wonder if I can install 386 and 486 CPU at the same time and just use jumpers to decide which to use?

That usually only works with a soldered cpu on a board meant to support

Otherwise

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Reply 12 of 17, by jakethompson1

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kixs wrote on 2022-07-23, 17:23:

Installing NT4 on 386 is pretty optimistic by any standard.

Try adding a FPU for test.

I didn't think NT 4 ran on a 386 at all because of COMPXCHG. But maybe the uniprocessor kernel does?

Reply 13 of 17, by Xeen

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rmay635703 wrote on 2022-07-23, 15:35:
That usually only works with a soldered cpu on a board meant to support […]
Show full quote
Xeen wrote on 2022-07-23, 10:14:

I always wonder if I can install 386 and 486 CPU at the same time and just use jumpers to decide which to use?

That usually only works with a soldered cpu on a board meant to support

Otherwise

7FCD8A9C-4CEA-43CB-9DCC-D88ACD75CEE1.jpeg

It seems the image is no longer exists, can you re-upload it?

Reply 14 of 17, by darry

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Xeen wrote on 2022-07-24, 01:03:
rmay635703 wrote on 2022-07-23, 15:35:
That usually only works with a soldered cpu on a board meant to support […]
Show full quote
Xeen wrote on 2022-07-23, 10:14:

I always wonder if I can install 386 and 486 CPU at the same time and just use jumpers to decide which to use?

That usually only works with a soldered cpu on a board meant to support

Otherwise

7FCD8A9C-4CEA-43CB-9DCC-D88ACD75CEE1.jpeg

It seems the image is no longer exists, can you re-upload it?

It works fine for me .

Reply 15 of 17, by Xeen

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darry wrote on 2022-07-24, 02:22:
Xeen wrote on 2022-07-24, 01:03:
rmay635703 wrote on 2022-07-23, 15:35:

That usually only works with a soldered cpu on a board meant to support

Otherwise

7FCD8A9C-4CEA-43CB-9DCC-D88ACD75CEE1.jpeg

It seems the image is no longer exists, can you re-upload it?

It works fine for me .

It is working now 😀

Reply 16 of 17, by NScaleTransitModels

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Update: I sold the mobo that was giving me problems (made sure to state "486 only"). Then by pure chance, I bought a mystery beige box, and opened it up to find an Acer VI9 386/486 VLB mobo. It already had a 486DLC installed, so I went ahead with the "NT4 killer test". No crashes, no errors, and memtest passes as well. Definitely doing a build around this one. I guess the other mobo may have had a design flaw (unconnected lines?) in its 386 mode.

Xeen wrote on 2022-07-23, 10:14:

I always wonder if I can install 386 and 486 CPU at the same time and just use jumpers to decide which to use?

Have actually tried this on a FX-3000 386/486 mobo. It wouldn't boot with CPUs in both sockets, but fortunately, no flamethrowers were manufactured.

Builds:

  • PCChips M321; 386DX-25@40; PVGA1A, ISA 512kb
  • Acer VI9; 486DLC-40; Mach32, VLB 2mb
  • Chicony CH-471A; CX486s-40; Mach32, VLB 2mb
  • Gateway 2000 P5-60; Pentium-60@66; S3 928, PCI 3mb
  • DTK PKM-0033S; AM5x86-133@160

Reply 17 of 17, by NScaleTransitModels

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jakethompson1 wrote on 2022-07-23, 18:50:
kixs wrote on 2022-07-23, 17:23:

Installing NT4 on 386 is pretty optimistic by any standard.

Try adding a FPU for test.

I didn't think NT 4 ran on a 386 at all because of COMPXCHG. But maybe the uniprocessor kernel does?

How do I switch to uniprocessor kernel? Is it an option during setup?

Anyhow, I've already done some testing of NT on 386-class CPUs.

NT 3.51: runs on 386
NT 4.0: no install, no boot on 386. Runs fine on 486DLC
NT 5.0 build 1906: Installs and runs on a 486DLC, but you have to be careful to not trigger CHKDSK, which will freeze at every boot.
2000: With 486DLC, BSOD "KMODE EXCEPTION NOT HANDLED" booting the last phase of setup. Have tried a few motherboards.

FPU made no difference in installation or ability to boot, but in NT5+, it is required for any sound drivers to work.

Builds:

  • PCChips M321; 386DX-25@40; PVGA1A, ISA 512kb
  • Acer VI9; 486DLC-40; Mach32, VLB 2mb
  • Chicony CH-471A; CX486s-40; Mach32, VLB 2mb
  • Gateway 2000 P5-60; Pentium-60@66; S3 928, PCI 3mb
  • DTK PKM-0033S; AM5x86-133@160