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Silicon Integrated Systems 486 Motherboard

Biomation

New Member
Joined
Sep 27, 2023
Messages
1
I bought a SIS 486G 3.3/5Vb Ver:I motherboard off of E-bay, complete with manual. This board is supposedly New Old Stock, and is very clean. Upon arrival, I promptly pulled the ni-cad battery, although it showed no signs of corrosion. I've installed a Intel 486DX2 66 CPU and RAM from a 486 board with damaged traces from a leaky ni-cad battery. I've configured the jumpers per the manual for the CPU type and RAM. But I'm not getting any POST codes on a POST card, just dashes. No beeps from the speaker either. With an oscilloscope, I've confirmed clock output from the clock chip. I can also see activity on data and address lines with the scope. I've since learned after purchasing it that this board likely has fake CACHE SRAM chips as they are labeled 'WRITEBACK' in big letters. But these shouldn't keep it from POSTIng, right? Does anyone have experience with these boards? Any thoughts on what to try next?
 

GiGaBiTe

Veteran Member
Joined
Apr 30, 2015
Messages
3,323
Location
Austin, Texas
You can ignore the cache chips if they're obvious fakes. The traces to them probably go nowhere, or are in loops under the chip to make them look like they go somewhere.

I can't seem to find your version of the board, just the D/E/G versions, which have real DIP cache chips on them.

For memory, what kind of memory are you using? 30 pin SIMMs or 72 pin SIMMs? If the former, you'll need to populate all four modules to make up the full 32 bit 486 bus. With 72 pin SIMMs, you just need one.

If you're getting activity on the data and address bus, that's at least something. You may want to pull the BIOS chip and dump it to see if there's any obvious problems. Finding an appropriate BIOS for the board may be a challenge, but you can try one from another revision of the board, just make sure you keep a backup of the original.
 
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