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Weird OMTi 486 mb

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First post, by Al Kossow

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Has anyone ever seen a board like this before?
No manufacturer, no 8042 keyboard controller and no obvious CPU clock generator.
Of course, all of the jumpers and cache rams are missing too

and OPTi not the disk controller company OMTI

are there any OPTi 895 motherboard schematics out there anywhere?
I don't see anything obvious in the chip set data sheets to provide clock generation or keyboard controller
functionality.
i'm guessing the RTC functionality is in the 602

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Reply 1 of 22, by mkarcher

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Al Kossow wrote on 2022-05-18, 20:27:
Has anyone ever seen a board like this before? No manufacturer, no keyboard controller and no obvious clock generator. Of course […]
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Has anyone ever seen a board like this before?
No manufacturer, no keyboard controller and no obvious clock generator.
Of course, all of the jumpers and cache rams are missing too

i'm guessing the RTC functionality is in the 602

You are right about the RTC, also the keyboard controller is integrated in the OPTi (not OMTi) 82c602. Integrated keyboard controllers are quite common on late 486 boards, mostly those that also provide PCI slots. Your baord seems to be one of the earlier boards without a dedicated keyboard controller.

Reply 2 of 22, by Al Kossow

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I posted about this on Twitter, and someone replied with
Re: Bought these (retro) hardware today "Another SIS471 — no BIOS chip."

So, it looks like someone went through a lot of trouble to put another chipset on my board
The OPTi and SiS don't appear to be pin compatible, and the one that was found has the cache
rams and jumpers.

fwiw, the ID string on my AMI EPROM is 40-E300-001437-00111111-121593-GREEN
it is on line in https://www.ultimateretro.net/en/motherboards/6821#downloads

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Reply 3 of 22, by Anonymous Coward

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Now THAT is interesting. I've never seen anything like this before....just claims that OPTi was really a clone of something else. Maybe this is the board that helped create this rumour.

There could be explanations for it. Perhaps by this time OPTi was focusing on their Pentium chipsets and didn't have the resources to create a new 486 chipset, so made an agreement with SiS to license theirs and sell under the 895 lable.

OR, maybe this board is like some PCchips crap with a knockoff chipset that has a special sticker or silkscreen to please OEM customers.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 4 of 22, by Al Kossow

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There are 895 and 895A parts, the same as 602 and 602A. There is an addendum describing the 602A but I couldn't find anything for the 895A
I'm going to check power and ground pins to see what my parts use and if they match with the SiS471 . It hadn't even occurred to me the A rev part might be a different pinout

Something else I just noticed is the SiS datecodes are months earlier than the OPTi

Also, an odd coincidence that my BIOS eprom matches a PC Chips mb with ASICS in the same packaging.

Reply 5 of 22, by Tiido

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SiS471 and OPTi895 definitely do not share pinout and have different register layout etc. so clones these two are not. Datasheets of both are available for comparison.

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Reply 6 of 22, by Anonymous Coward

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It's too bad that the 895 chip didn't actually say "OMTI", then we would could rule out at least one of the possibilities of what the chip actually is.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 7 of 22, by weedeewee

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Al Kossow wrote on 2022-05-21, 00:02:

Also, an odd coincidence that my BIOS eprom matches a PC Chips mb with ASICS in the same packaging.

yep, odd indeed, especially since those mainboards use umc chips, relabeled to pcchips🙂

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Reply 8 of 22, by Al Kossow

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I think this is going to just be a dead end that goes in the scrap pile.
I could try swapping out the two ASICs and populating the cache ram
and jumpers to match, but then there is the problem of the unknown
BIOS. It did also point out there are no data sheets online for the
SiS 85C407

Reply 9 of 22, by computerguy08

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Al Kossow wrote on 2022-05-18, 20:27:
Has anyone ever seen a board like this before? No manufacturer, no 8042 keyboard controller and no obvious CPU clock generator. […]
Show full quote

Has anyone ever seen a board like this before?
No manufacturer, no 8042 keyboard controller and no obvious CPU clock generator.
Of course, all of the jumpers and cache rams are missing too

and OPTi not the disk controller company OMTI

are there any OPTi 895 motherboard schematics out there anywhere?
I don't see anything obvious in the chip set data sheets to provide clock generation or keyboard controller
functionality.
i'm guessing the RTC functionality is in the 602

This is a super bizzaire situation, same PCB with 2 completely different chipsets.
The included ROM chip from yours is for an UMC board, to make things even more confusing (though I doubt it's original to the board)

Don't throw this board away, I feel like it has an important significance in uncovering some truth behind these chipset relabels from back then.
It would be nice if you could try these BIOS images (providing multiple varians in case of a chipset relabel) and report the outcomes, POST codes and/or beep codes:
- OPTI 895 (from my Jetway board, I recommend using the Award BIOS): https://www.ultimateretro.net/en/motherboards/5505#downloads
- SiS 471: https://www.ultimateretro.net/en/motherboards/4652#downloads

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Reply 11 of 22, by Al Kossow

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well, I keep poking around and looking at pictures
based on parts used and layout, it really seems like it is a Soyo board, but nothing quite matches it in
https://web.archive.org/web/20010619055022if_ … 86/25J-MU43.PDF
it was probably a 20 series, but earlier than anything IA saved

IA is acting really weird. I found a path where you can get to their archived manuals and bios, but now I can't find the URL

I'm going to throw them up on http://bitsavers.org/pdf/soyo

Reply 12 of 22, by Anonymous Coward

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I've never seen that weird SIMM spacing on a Soyo board. Looks like something PCchips would do.....just like the M919.

"Will the highways on the internets become more few?" -Gee Dubya
V'Ger XT|Upgraded AT|Ultimate 386|Super VL/EISA 486|SMP VL/EISA Pentium

Reply 14 of 22, by WJG6260

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While this may only be tangentially relevant to this thread, I think it's worth adding, nonetheless.

I have had an FX-3000 motherboard for a while, and when I first received the board swapped the EPROM for an EEPROM loaded with the UMC480's corresponding MR-BIOS. I recently came across the original EPROM for this board and finally dumped it and noticed that it references an OPTi chipset! Now this is especially odd because the actual chipset is, as aforementioned, the UMC480!

Like the OP's board, this board seemingly has a BIOS that's either mismatched for the chipset and was just slapped on the board, or there's more at play here. I think it's certainly interesting to note that a supposed OPTi BIOS worked just fine in a UMC480 board.

Now I have no idea as to whether this BIOS is original to the board, but the sticker on the BIOS matches the keyboard controller and the board was sold as NOS--and seemingly was indeed in such condition, when I first received it a few years ago. The OPTi BIOS worked totally fine, except 486 support was nonexistent. 386s of all variations worked correctly.

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Reply 15 of 22, by Tiido

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UMC has a history of cloning stuff (*coughNEScough*)

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 16 of 22, by WJG6260

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I wonder what chipset the UMC480 could be a clone of? Perhaps the OPTi 491/493?

I wonder if this lends any credence to the theory that some chipsets are just GAL chips made by Toshiba, like the PCCHIPS SARC ones?

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Reply 18 of 22, by Tiido

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Toshiba (NEC and many others) made ASICs for many companies. Gate arrays were pretty common products, with only metal layer(s) customisation needed to get the final design. Decap will tell for sure what exactly goes on inside. UMC was one of the companies that did silicon for others (and themselves), OPTi was a fabless company from what I know and used services of others to produce their chips. This makes me think that maybe there could have been a deal where UMC could sell OPTi made chips in their branding, like Cyrix, ST and IBM etc. did. UMC has definitely manufactured chips for OPTi, among other companies.

T-04YBSC, a new YMF71x based sound card & Official VOGONS thread about it
Newly made 4MB 60ns 30pin SIMMs ~
mida sa loed ? nagunii aru ei saa 😜

Reply 19 of 22, by Al Kossow

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I just made a table of 100 pin integrated peripheral controllers
http://bitsavers.org/projects/486_motherboard … PeriphCtlrs.txt

I'm pretty confident the memory controller is a SiS 471, from tracing out power and ground on the 100 pin part that it isn't a 407.
Just to verify the 407 pinouts from the schematic I found, I bought a mb with a 407 on it, and the power and grounds match
So.. that part on my board doesn't match anything known.

Also, it would be nice if someone has already traced out the winbond and umc parts if I could get that information rather than
having to beep them out.