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486 VLB UMC-Chipset, what is it?

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First post, by gerwin

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Today I was at talking to someone who still had a 486 in a corner of his office. He claimed it should still be running even though he had not touched in at least 10 years. So I pressed the power button, and it booted up fine, straight to the windows 95 Desktop. He was so kind to give it to me, as long as I destroyed and returned the harddisk, and I am supposed to take the yellowed screen and keyboard too.

It has been like 10 years since I touched a system this old myself, so I am still trying to figure out what I am dealing with here. Unfortunately I don't have much time now.

EDIT: updated the info below
Case: Baby AT with a 'Target' case sticker. A 200W 'Target' PSU is at the bottom and the VLB slots are at the top. Assembled Week 2 1995.
CPU: Cyrix Cx486 DX2v66. Set to 3,45 Volt. No heatsink or fan.
Motherboard: TK 8498F /GP 4N D24, Socket 3, UMC UM8498F Chipset. 4xISA, 3xVLB. 256kB cache. AMI WinBIOS 1993. PCB week 46 1994.
VLB Multi-IO+VGA+IDE: UM-85C418 'Super VGA', 1MB 80ns, VESA 1.2a, max 1024x768x8 / 800x600x16 / 640x480x24. PCB week 28 1994.
Memory: 2x 4MB 72-Pin 70ns. Four 30-pin slots still empty.
Sound: ISA Aztech Waverider32, with 2MB Wavefront Wavetable, OPL3 and CD+IDE interfaces. PCB week 38 1994.
Modem: ISA 14k4, Rockwell.
Harddisk: Conner 94112-042, 420MB, 3.5" IDE, Type 47.
Removables: Floppy 3,5". CD-ROM 48x (connected to sound card), Tape streamer 'Colorado 250MB' (as floppy slave).
Input: Serial mouse and DIN keyboard.

I do have an Enhanced Am486 DX4-100 chip in my drawer, I suppose I could install that one too. Is that without jumper changes and does it work well without a heatsink? What are these LED jumpers for?

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Last edited by gerwin on 2014-04-05, 18:53. Edited 15 times in total.

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Reply 1 of 75, by MMaximus

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Nice find. The jumpers near the LED display allows you to specify a speed to display when turbo button is on and another one when it's off. It takes a bit of trial an error but you should be able to figure it out.

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Reply 2 of 75, by Kamerat

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gerwin wrote:

I do have an Enhanced Am486 DX4-100 chip in my drawer, I suppose I could install that one too. Is that without jumper changes and does it work well without a heatsink? What are these LED jumpers for?

100 doesn't fit in that LED display... 😲 What does the display show with that configuration?

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Reply 3 of 75, by MMaximus

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the LED display is completely independent of system speed. it was set by the computer manufacturer or reseller, and if later you upgraded your CPU you would have to change the display with the jumpers if you wanted the correct speed to be displayed.

Hard Disk Sounds

Reply 5 of 75, by Robin4

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I think i have the same motherboard here.. Also i have that combo I/O, VGA VLB adapter here.. The last isnt working for me.. But iam trying finding out how to repair it..

Look on the underside of the board on the left side...

Maybe you will find:

TK 8498F /GP 4N D24.

Iam not 100% sure, but i think the board was made by ADI..
The board also could made by aqua systems., but in my experience, the layout on your board matching my TK 8498F /GP 4N D24 board.

I think the multi I/O could be made by ADI also because of TK in the line.. Most manufacturers using the same first letters on a product..

I also think that this mulit I/O was specially made for that board... But that multi i/o isnt a really good performer.. Because back in the days, when they combine everything on one board, that was to cut the costs on the total value of the system. I guess its having only 1MB for the VGA part.

Can you made send my a picture of that multi I/O also on the left part of that board.. I want to see what settings is made on your card (because mine doesnt seems to work) (i like the see JP3 till JP8)
otherwise iam think of recapping it.

ftojfs6hfso8yw1upyo3_thumb.jpg

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Pictures are clickable for bigger ones.

Look ADI uses TK in his product names:

http://www.elhvb.com/mboards/adi/tk8881/TK8881man.html

Here you should find a little manual for that board.
http://www.elhvb.com/mboards/adi/Index.html

Last edited by Robin4 on 2014-04-03, 00:18. Edited 1 time in total.

~ At least it can do black and white~

Reply 7 of 75, by gerwin

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Robin4 wrote:

Maybe you will find: TK 8498F /GP 4N D24.

Yes that is it!, but the other silkscreening markings are not there on my board. The quoted line is the only identification. I got more findings, but don't have much time to write about it now.

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Reply 8 of 75, by gerwin

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Okay guys, regarding the LED: It shows 66 by default, and 10 with turbo switch OFF.
Thanks for the info on that part.

I now know a little more about the board and the cards, and will update the original post with the new info.

The SD Card to IDE adapter works with it. At first it only liked a small 64MB SD Card. At least I could boot to DOS fast, run tests, play a few games and exchange data. Much more comfortable already. Using custom Disk-parameters in the BIOS the 2GB one now works as well. I would like a PS/2 mouse too, if that is at all possible.

This Cx486 DX2v66 has actually been running for years without a heatsink. I ran a few benchmarks yesterday:
- SpeedSys: 26,59 pts.
- PC player benchmark at default 640x400: 4,8 FPS
- Superscape 3D-bench: 41,6 FPS
AFAIK these scores are typical for a DX2-66. Doom 1 runs fine.

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Using the jumper settings found >>Here<<, the Am486DX4-100SV8B now works on this board. But it underperforms in all the benchmarks? I expected 20% more then this. Still a notch up from the DX2. I will have to investigate if the CLKMUL pin is configured properly to 3x 33MHz.
- SpeedSys: 32,34 pts.
- PC player benchmark at default 640x400: 5,7 FPS
- Superscape 3D-bench: 52,6 FPS

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Robin4 wrote:

I also think that this mulit I/O was specially made for that board... But that multi i/o isnt a really good performer.. Because back in the days, when they combine everything on one board, that was to cut the costs on the total value of the system.

Agreed, it is all UMC brand, and the card fills the missing options of the mainboard. It is easy to imagine Disk I/O interfering with VGA I/O on the same VLB Slot. At least the card should be very compatible with the motherboard. I kinda like UMC, if only because it is such a typical 486 brand. Here are the photos:

High resolution variants here: Mainboard total, Socket area, Socket area side, Multi I/O VLB card

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(condensators near VRM are both 47 micro-Fahrad, 16V)

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(The red wire of the HDD LED connector goes where i put the blue jumper on this card, on the left.)

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Reply 9 of 75, by Robin4

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Can you tell me what the missing options where when that multi- i/O card was installed? Where does options important?

Can you also tell me the values of those capacitors between resistor r54 and r53 (now they are on the downside from the VRM) The values are listed on the black coating of those capacitors..
There need to be a voltage on them and a uF (microfarrad value) Sorry but i can see them on your picture, because the values are written on the other view angle.

It seems that your Multi i/O card have recapped in the past.. Mine card still have its original black ones.. But mine card doesnt seems to work.. But iam trying to repair it..

~ At least it can do black and white~

Reply 10 of 75, by gerwin

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It is written above the picture, "capacitors near VRM are both 47 micro-Fahrad, 16V". I wrote 'condensators' there in error, but you should understand that word too. 🤣

With 'missing options' I meant just the headers for IDE, COM 1+2 and LPT port. On later ATX boards, and some AT boards, these things were already part of the motherboard.
Maybe your VGA BIOS is bad?
The previous owner was not technical at all, it very unlikely that anything inside this case has been serviced since week 2 1995. It is just an artifact of that time.
Edit: Correction, the 48x CD-ROM drive is not from 1995, for one. The documentation shows that the system was originally delivered with a double speed CD-ROM drive from Aztech, type CDA 268-031 SE.

Like we talked about in PM, I am definitely interested in backing up this EPROM BIOS and replacing it with a modded EEPROM one. But I don't have an EEPROM writer, like you do IIRC.

Yesterday I was trying to figure out why the am486DX4-100 is underperforming. But without a proper layout of this board it is hard to make notes, so I made a new layout with a vector paint program myself. With all jumper locations clearly visible. It will get uploaded here when it is finished.
First I tried to toggle the CLKMUL pin of the processor, but I got weird results. It appears later am486DX4 chips moved CLKMUL to another pin, and have the WriteBack enable pin on that place instead. The weird result is that the system currently does not properly support Writeback cache. When WB was enabled it resulted in disabled motherboard cache and unreliable bootup.
So with a newer datasheet the actual CLKMUL pin was located, and soon the CPU ran happily at 2x 😀 . The Speedsys score for the am486DX4 at 66MHz is 24,10 pts.
(edit:typos)

Last edited by gerwin on 2014-05-18, 20:38. Edited 2 times in total.

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Reply 11 of 75, by Robin4

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Ok those `missing options` where not that important.. It was then just normal when the I/O parts where on a seperate board. That was till 486 PCI boards came out more manufacturers inplanted the I/O to the motherboard. But when the Pentium 1 boards came out, then it was also possible to boot from CD players. I have two VLB boards here that came with i/o already.. The first one is the chicony CH-471B Rev 1.0 and the second chicony CH-471B Rev 2.0. Those boards also supports bigger harddisks (i think till 8.4GB) So PCI boards didnt where the first boards available with i/o on the board it self (also some FIC 486 boards came with it)

About the VGA bios.. I dont know if this eprom is bad, i had it already in my programmer and it would look fine.. If you maybe can send a copy from you i might try it out and see if its indeed flat..
But i also had use a magnified glass and looked on the legs from the SMD chips.. On the VGA chip there was a little leg bent. I had it already bent it back so it dont make a connection anymore. Otherwise i might reflow that part of the chip and see that could maybe the problem. Iam also thinking of replacing the caps.. The electolyte in the capacitor could be dried out, so that also can explain why its not working anymore.. But i hope i can repair it in the near future.

The settings on the right side near the cpu socket are all in a vertical position. But never looked further on the technical side on CKLMUL.. Did you know which batches are the good ones? and which are the bad ones?

Thanks for re-writing the capacitor values, i didnt found then elsewhere)

~ At least it can do black and white~

Reply 12 of 75, by feipoa

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gerwin wrote:

I would like a PS/2 mouse too, if that is at all possible.

I am curious how you will pull this off...

Plan your life wisely, you'll be dead before you know it.

Reply 13 of 75, by gerwin

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Last week I went to the previous owner again to free him of the CRT monitor, mouse and keyboard, as promised. So there was an opportunity to ask about documentation and/or a driver disk. Luckily he still had everything, all the manuals and all the floppies! Actually I already suspected he had that stuff stored, the main question was if it could be found.

The VGA drivers 'UMC418' look identical to a package from driverguide, but there is a big difference: the driver now actually recognizes this combo card. The windows 3.1 drivers work well in Windows 95, though one cannot select a different screen mode without changing the driver file. There is also a utility to change default refresh rates in DOS. The card works well in EGA, MCGA and VGA modes. Getting it to run 640x400x256 and higher does not always work. It has a scrolling problem with Commander Keen games, visible on the far right 10 millimeters of the screen. The card has jumpers to disable all the Multi I/O interfaces seperately, but an option to disable the VGA part is not mentioned.

The manual for the motherboard is labeled 4DXL-UX and F4DXL-UC4D. I scanned all pages and made it into a pdf, which will get uploaded to vogonsdrivers later. Same for the UMC Multi I/O card manual. Maybe the Waverider 32+ too, if anyone cares for it.
On the topic of documentation; datasheets for UMC chipsets are nowhere to be found.

The problem with the underperforming am486 is solved. Using the BIOS options to manually set the cache read/write waitstates to the minimum. This is mentioned in the official am486 FAQ. It now scores 37,5 pts in SpeedSys, 6,5 FPS in PCB and 66,6 FPS in 3Dbench. Windows 95 now works a lot better. Earlier I could not even listen to some midi files without having to wait 9 seconds for the stock media player to load.
Because of the am486 windows 95 problem I had already been looking around for another CPU. I considered the AMD x5, but it seems to be the same am486 with the multiplier settings raised. I went for an Intel 486 DX4-100 Write-back instead, sSpec SK096, which will arrive next week. Also incoming are a bunch of EEPROMs for the BIOS.

feipoa wrote:
gerwin wrote:

I would like a PS/2 mouse too, if that is at all possible.

I am curious how you will pull this off...

Was trying out a few older optical PS/2 mice with some rewiring, to see if there was maybe a dual mode one. But no luck. The serial mouse that belonged to this system is alot better then my previous serial mouse, that will have to do.

Robin4 wrote:

The settings on the right side near the cpu socket are all in a vertical position. But never looked further on the technical side on CKLMUL.. Did you know which batches are the good ones? and which are the bad ones?

There is no good or bad, just an normal am486 and a so called 'enhanced' am486. They probably only differ in internal cache configuration and pinout, AFAIK AMD never increased the instructions per clock on any of their 486s. I think the later 'enhanced' ones were designed as a drop-in alternative for intel DX4-100 Write-back processors, as they have the same pinout.
You can find these datasheets on the net:
-am486: 19160D.pdf
-am486 'enhanced': 19225C.pdf
The motherboard documentation lacks seperate jumper settings for Write-through and Write-back processors. Which makes it difficult to properly configure the motherboard for a WB-capable CPU, even when the CPU is in WT mode....

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Reply 14 of 75, by Stiletto

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gerwin wrote:

On the topic of documentation; datasheets for UMC chipsets are nowhere to be found.

I know this well. They're one of the first major Chinese semiconductor firms of the 80's/90's (I think) and it shows in their lack of documentation. The first part of their life they were mostly churning out clone chips, so it wasn't a huge issue... but it became a problem for us when they started making their own custom chipsets, etc. At least, that's my interpretation.

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do the Fandango!" - Queen

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Reply 15 of 75, by gerwin

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Stiletto wrote:

I know this well. They're one of the first major Chinese semiconductor firms of the 80's/90's (I think) and it shows in their lack of documentation. The first part of their life they were mostly churning out clone chips, so it wasn't a huge issue... but it became a problem for us when they started making their own custom chipsets, etc. At least, that's my interpretation.

I even asked Mr. Steunebrink (the K6+ BIOS master) about UMC datasheets. Because his writings suggested he knew more. Unfortunately he does not have any datasheets either.
The documentation of the motherboard and VGA card is pretty bad indeed: Wrong spelling and typos. BIOS features described which are not there at all. It says for turbo it needs a jumper, but jumpering it slows the system. P24D (i486DX4 Write-back) jumper settings are listed, but that does not work of course.
It seems that a large batch of these UMC VLB boards was shipped to the Netherlands in 1994. Since Robin4, Tetrium and me all have the same board and matching Multi-I/O+VGA card.

There was some progress this week: The board was equipped with two faster 60ns SIMMs. Two 8MB 72-pin FPM modules giving me a maximum of 16MB. The 30-pin sticks have to be removed now, as they are only 70ns. The DRAM waitstate setting in the BIOS can now be set to zero, increasing the memory throughput by about 12,5%.
Playing 128kbps MP3s in windows 95 is now within reach. Using Winplay3. I still have to set frequency to half though.

The other new item is the expected intel 486DX4-100 (SK096).
At _66MHz it scores: 28,24 points in SpeedSys; PC player benchmark at default 640x400 gives 6,6 FPS.
At 100MHz it scores: 42,36 points in SpeedSys; PC player benchmark at default 640x400 gives 8,3 FPS.
In the exact same environment the AMD DX4 part scores the following:
At 100MHz it scores: 37,47 points in SpeedSys; PC player benchmark at default 640x400 gives 7,0 FPS.
Like Feipoa already showed very nicely in his 486 benchmark, the intel DX4 part has some noticable enhancements compared to the DX/DX2. Where the AMD part is mostly just a higher clocked original DX.

With the intel DX4-100 I am still limited to Write-Through mode here. but already a game like Comanche Maximum Overkill runs too fast (speedlock=off). 🤣 66MHz mode will take care of that.

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Reply 16 of 75, by gerwin

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It was advised here to immediately remove old barrel batteries, even when they look or work fine. So I did that today. It seems to work well with the usual 3 Volt CR2032 button cell. The red wire is the positive terminal connected to JP1 pin 1. The negative terminal is soldered to the old battery negative terminal, instead of the connection to JP1 pin 4. This is electrically the same and allows me to fix this holder to the motherboard.

I have to leave the red jumper in place at JP1 2-3, because without it the system will be counting only half the time that actually passed?

Did not dare to use the old barrel battery positive terminal. As pointed out on this forum it is intended for rechargeable batteries only. The old battery is labelled 3,6V, GP60BNKX3, Ni-Cd, GP SYLVA Charge. Rechargeable allright.

The cable connected just to the left of the BIOS is there to take 5 Volt power from that pin, to supply power to the SD Card to IDE adapter. I prefer taking power from the motherboard where possible. So now I don't have to bother with the PSU other then the main power connector P8/P9. The IDE adapter has a 2GB SD card, with the following BIOS settings; Cylinders=15080; Heads=8; Sectors=32. LBA set to enabled.

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The package for TK8498F motherboard and VGA+Multi-I/O card is now uploaded to Vogons Drivers. It includes a new layout that I made for this motherboard, a proper one.

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By the way, The Aztech sound card was removed early on. It was replaced with a CMI8330 SB16+WSS compatible sound card, with Wavetable daughterboard attached. I will keep the Aztech stored until maybe someday it get interested in it.

Last edited by gerwin on 2018-12-02, 16:04. Edited 2 times in total.

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Reply 17 of 75, by Robin4

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Unbelievable i really like your drawing skills. Maybe its a good idea to make a archive of older 486 motherboards.

~ At least it can do black and white~

Reply 18 of 75, by gerwin

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Glad you like it.
I suppose old hardware is much more useable with the proper documentation and/or drivers. So storing and sharing what we still have is a great idea.
Look what I found: UMC Computer IC Data book 1990/1991. If only it was the 1993/1994 edition...

The Battery mod has a problem. The system again loses track of time whenever it is powered off... 😠 Either the circuit does not have proper support for an external battery, or the CR2032 voltage is too low for the real time clock to tick. BIOS settings remain saved though.

There is a small typo in my PDF version of the layout: 20MHz FSB is set by removing all jumpers. I don't know how to Update the entry at Vogons drivers without deleting it first?

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Reply 19 of 75, by feipoa

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Could you use the existing barrell battery solder points for the CR2032 but cut the connection to the charging lead, similar to what I did on this motherboard, Native PS/2 mouse implementation for 386/486 boards using the keyboard controller

Plan your life wisely, you'll be dead before you know it.