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Mikrolog Osborne 486DX 33Mhz

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First post, by hahokas

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Hi,

I'm new to the board, so please excuse my short comings in board etiquette. Also English is my second language so excuse for that also.
So to the point of the subject.

I have recently find my first PC from my parents house. This is from the time that I wasn't so much in to the hardware side of it's inner workings. That came later for me at the Athlon era.
I'm interested in restoring it to it's former glory. But frantic googling hasn't given me all the answers, so i must seek higher knowledge of the inner workings of the 486 era computers.

So it's a clone machine from mid 90's, but together in Finland by Mikrolog Ltd that had acquired the Osborne computer trademark.

Some specs that i have managed to dig up so far:
Full model: Osborne LP4D-33-L3 LH-2306-01 (-94)
CASE: Clone design case in Pizzabox/breadbox form factor
CPU: Intel i486Dx 33 MHz
MEM: 16 MB's of memory of some kind, original amount consisted 4MB
HDD: is missing, but it used to have Western Digital WDAC2340 325MB drive in it
FDD: also missing, but it must have been some generic 1,44M 3,5"
MB: it seems to be a UMC chipset board, with Cirrus Logic CL-GD54228-80QC-A LBA VGA adapter built in to it.
5 ISA slots on a riser card.
31-XP9486L-[BLANK] this is the only resemblence of a modelnumber on the motherboard.
BIOS: AMIBIOS 40-0100-000000-10111111-040493-UMC491-H
PSU: Chiu electronics P-2005S 200W

If I remember correctly, I did have Sound Blaster AWE32 and CD-ROM drive in there, but they seem to be lost in time.
Also I have tried to get a CF card adpater working for the software installation side.

Machine boots up and after I soldered new Lithium battery on it remembers the BIOS settings.

My question being, how can I decipher the motherboard, if I there is any upgrade paths to take, more memory, faster CPU, adding L2 cache, better graphics, sound card.
And if there's any generic info about the machine and it's motherboard, that would be much appreciated.
And what BIOS settings can or should be changed?

Purpose for me is the tinker with the machines hardware and play period accurate games. Mayby some windows 3.11 nostalgia.

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Last edited by hahokas on 2021-09-09, 17:25. Edited 2 times in total.

Reply 1 of 26, by Eep386

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UMC 491 chipset? That's almost a guarantee of a 5V CPU only board as that chipset was very common on 5V boards. Your best bet for CPU upgrades would be an Intel 486DX2 of some flavor, or if you find one on the cheap, maybe an Intel Overdrive DX4-100 or an Am5x86 upgrade chip (not a straight Am5x86, but rather one seated on an interposer board which has its own regulator).

16MB is pretty standard for a 486, only add more if you plan on running Windows 95 or some memory hogging game.

That Cirrus 5428 onboard isn't too bad so you don't need to fuss with that right away. Sometimes they come with only 512K memory on these systems though, which halves its SVGA throughput.

Given the 04/04/93 date code of the AMI BIOS, I'm willing to wager it's pre-LBA, so you're probably limited to hard drives under 503MB unless you use something like Ontrack Disk Manager.

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 2 of 26, by hahokas

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Eep386 wrote on 2021-09-09, 16:58:
UMC 491 chipset? That's almost a guarantee of a 5V CPU only board as that chipset was very common on 5V boards. Your best bet fo […]
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UMC 491 chipset? That's almost a guarantee of a 5V CPU only board as that chipset was very common on 5V boards. Your best bet for CPU upgrades would be an Intel 486DX2 of some flavor, or if you find one on the cheap, maybe an Intel Overdrive DX4-100 or an Am5x86 upgrade chip (not a straight Am5x86, but rather one seated on an interposer board which has its own regulator).

16MB is pretty standard for a 486, only add more if you plan on running Windows 95 or some memory hogging game.

That Cirrus 5428 onboard isn't too bad so you don't need to fuss with that right away. Sometimes they come with only 512K memory on these systems though, which halves its SVGA throughput.

Given the 04/04/93 date code of the AMI BIOS, I'm willing to wager it's pre-LBA, so you're probably limited to hard drives under 503MB unless you use something like Ontrack Disk Manager.

This is just what I needed, thank you very much!

Edit:
Does the hard drive need to be under 504MB or is it enough that the boot partition is under that size?

Last edited by hahokas on 2021-09-09, 17:29. Edited 1 time in total.

Reply 3 of 26, by Eep386

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Sure thing, glad to help.
It sounds like the foundation of a pretty rad DX2 system though, so I'd like to see it up and running soon!

Those empty skinny DIP28 sockets lower center and right in the mobo shot are cache sockets, you'll want to find some 32Kx8 15ns SRAM chips to put in them.
The shorter empty DIP sockets just above the Cirrus 5428 controller are empty sockets for 256Kx4 DRAM chips. 70ns ought to be sufficient, 60ns will work too but be sure you're getting FPM DRAM, not EDO.

The empty rows of pins around the CPU also hint at potential compatibility with the Intel Pentium Overdrive POD-83 too. Good luck finding one at a semi-reasonable price on eBay these days though.

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 5 of 26, by Eep386

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Yeah those look like they'll work, though I wish they'd provide an actual picture of the UMC cache chips.

Yes, the hard drive must format to be 503MB or less for old AMI BIOSes. Easy fix is to just use Ontrack Disk Manager, I use it and it works great. You set up the HDD as a 1024 cylinder 16 head 63 spt drive in BIOS, and Ontrack translates the drive's actual geometry so that you get the full capacity of the drive.
Use the 9.57 version on this page.
https://www.philscomputerlab.com/ontrack-disk-manager.html

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 6 of 26, by jakethompson1

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hahokas wrote on 2021-09-09, 17:18:

Edit:
Does the hard drive need to be under 504MB or is it enough that the boot partition is under that size?

In addition to Ontrack Disk Manager already mentioned, another solution is to add an XT-IDE BIOS chip on an ISA card. Also, if you don't need more than 504 MB, you can just use a bigger drive, and will work as a 504MB one.

Be aware that the UM491 chipset does not support robbing a bit from the Tag RAM to use as a dirty bit, and it doesn't look like your board has a separate Dirty (Alter) RAM. So, it may use an "always dirty" strategy. Adding cache is still better than no cache, but if you start benchmarking you will find the benefit underwhelming compared to another board (like the newer UM498 chipset) that implements the write-back strategy properly.

I'm confused by your board in that it looks like there are IDE and floppy enable/disable jumpers but I don't see the connectors.

Reply 7 of 26, by Eep386

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I can see the floppy connector just above that topmost SIMM.
I assume the IDE connector is simply obscured by that SIMM in the photo.

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 8 of 26, by jakethompson1

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Eep386 wrote on 2021-09-10, 02:46:

I can see the floppy connector just above that topmost SIMM.
I assume the IDE connector is simply obscured by that SIMM in the photo.

Ah. Because then at the top right corner there are a bunch of missing components for a VLB IDE controller. But I wonder where the second IDE connector would go?

Reply 9 of 26, by hahokas

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jakethompson1 wrote on 2021-09-10, 02:51:
Eep386 wrote on 2021-09-10, 02:46:

I can see the floppy connector just above that topmost SIMM.
I assume the IDE connector is simply obscured by that SIMM in the photo.

Ah. Because then at the top right corner there are a bunch of missing components for a VLB IDE controller. But I wonder where the second IDE connector would go?

Yes there is one IDE connector and it's behind that topmost SIMM.

Reply 10 of 26, by hahokas

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So could the 503 MB limitation be circumvented by some ISA IDE controller card, witch would have it's own connectors and support for larger drives?
Just to get the boot drive below that limitation?

Reply 11 of 26, by Eep386

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It could, but the ISA IDE card must be configured as a secondary IDE port if the motherboard IDE is to be left enabled.
XT-IDE BIOS does detect drives on both ports in the 'default' add-in ISA card configuration, IIRC.

I think the pads for the PDC controller chip are for an optional VL-bus IDE controller, which was not fitted. This would implicate that the onboard IDE is ISA anyway.

Life isn't long enough to re-enable every hidden option in every BIOS on every board... 🙁

Reply 12 of 26, by hahokas

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Eep386 wrote on 2021-09-10, 02:26:
Yeah those look like they'll work, though I wish they'd provide an actual picture of the UMC cache chips. […]
Show full quote

Yeah those look like they'll work, though I wish they'd provide an actual picture of the UMC cache chips.

Yes, the hard drive must format to be 503MB or less for old AMI BIOSes. Easy fix is to just use Ontrack Disk Manager, I use it and it works great. You set up the HDD as a 1024 cylinder 16 head 63 spt drive in BIOS, and Ontrack translates the drive's actual geometry so that you get the full capacity of the drive.
Use the 9.57 version on this page.
https://www.philscomputerlab.com/ontrack-disk-manager.html

This seems to be a good solution for the problem!

Reply 13 of 26, by hahokas

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Eep386 wrote on 2021-09-09, 17:26:
Sure thing, glad to help. It sounds like the foundation of a pretty rad DX2 system though, so I'd like to see it up and running […]
Show full quote

Sure thing, glad to help.
It sounds like the foundation of a pretty rad DX2 system though, so I'd like to see it up and running soon!

Those empty skinny DIP28 sockets lower center and right in the mobo shot are cache sockets, you'll want to find some 32Kx8 15ns SRAM chips to put in them.
The shorter empty DIP sockets just above the Cirrus 5428 controller are empty sockets for 256Kx4 DRAM chips. 70ns ought to be sufficient, 60ns will work too but be sure you're getting FPM DRAM, not EDO.

The empty rows of pins around the CPU also hint at potential compatibility with the Intel Pentium Overdrive POD-83 too. Good luck finding one at a semi-reasonable price on eBay these days though.

I’we got mail. Those cache chips came, but not sure how to make them available for the processor. Is there bios setting or jumpers to adjust?

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Reply 14 of 26, by hahokas

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It must be the jumpers J6-J9. This was the result, so it must be detected then?

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Reply 17 of 26, by hahokas

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evasive wrote on 2021-09-22, 18:51:

How that page came to be, that picture and BIOS specs are from my board? Anyway the manual of the jumpers is great!

Having bit of a issue with the floppy drive. Had one that was bad and needs to be sorted out, It didn't read the disks all the way to the end of them.
I had a GOTEK device ordered and now it's installed. But both of those have same kind of issue.
They won't update the contents of the disk if changed and listed with DIR, have to reboot the whole computer to change disk.
Changed the floppy cable, but that didn't help. GOTEK has FlashFloppy firmware and jumper is in S1 position, that should be the PC compatible mode. It was first at S0 and like that it didn't recognise drive at all in DOS.

Also CF card that I'm using seems bit slow on reading, or the adapter is bad. It makes the DOS start bit slow.

I succesfully got MS-DOS 6.22 installed after getting the dynamic overlay working with Ontrack, could that slow down the boot? Boot takes about few minutes with default DOS settings, nothing else is installed.

Again thank you very much for the interest and support for my little project!

Reply 18 of 26, by evasive

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Image is credited to you indeed. The page was already there before and it matched with your board.

Now that you got it to work quite far, do you think you can make a bios backup somehow so we can include that on the page?

Reply 19 of 26, by hahokas

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evasive wrote on 2021-09-28, 12:08:

Image is credited to you indeed. The page was already there before and it matched with your board.

Now that you got it to work quite far, do you think you can make a bios backup somehow so we can include that on the page?

That I can do, as of I get it to run again properly.

It seems to have some issues with the memory side of things. I was diagnosing the slow boot, as it got even slower as I started adding drivers for sound card and cd-rom and stuff. I took about 20-25 minutes to boot to dos.
So I stirpped everything out and started from above, just to get it fresh start, reset the cmos and all drives off.

First start after CMOS reset seems to go well, it sees the amount of memory correct 640kb conventional memory and then I would load the bios defaults and boot again it only sees about 500ish kb od conventional memory and booting stops after the memory test with no error.

I tried to get it working with only one 4MB stick of RAM and it gives CMOS memory mismatch error. There is some lack of knowledge from my part in the BIOS memory settings, to verify that they are correct.

Still havent tried all the stick individually. also there is little bit of corrosion in memory bank 2 or 3 slot in few pins. Have to address that.