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Issue with MSI 3113-7 386DX Mainboard

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First post, by egrath

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Hi,

i just finished my first ever retro PC build to play some games i used to play in the late 80s and early 90s. It's based around a MSI 3113-7 386 Mainboard and is working fine generally. But there's one issue:

It just runs at 16 Mhz (according to Checkit 3) even though a 33 Mhz CPU is installed. The CPU was already installed when i got the board and the previous owner didn't knew anything about it, so i can't tell for sure if the jumpers are in the correct positions. Unfortunately, there is no manual available and no printing on the silk screen to indicate which jumpers need to be set in which position.

This is the board in question:

board.jpg
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I assume the block of 4 jumpers bottom next to the cache module to be the selectors, but i'm not sure about it and don't want to risk damaging the board. Anyone has the same board and can give me any hints? Additionally, what might be interesting or could help: There's a header on the board for the usual indicators like power led, reset, and so on. There's also one for "TURBO". If this one isn't closed the board does not boot at all.

With best regards,
Egon

Reply 3 of 5, by TheMobRules

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The picture in The Retro Web (https://theretroweb.com/motherboards/s/msi-3113-7) shows a board apparently configured for 25MHz and all 4 jumpers in the JP2 block are closed. You could try that, if that configuration works for that board (50MHz oscillator divided by 2) it should be no different on yours for 33MHz (66MHz oscillator divided by 2).

Reply 5 of 5, by egrath

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Yes, that's exactly the behavior of the device. In the meantime i was able to solve the issue.

Problem seems to be related the way the BIOS handles it's CMOS settings when the backup battery was disconnected. Essentially, there are two BIOS parts in the device: The basic one, which let's you specify basic parameters like date, time, floppy and hdd configuration. And the second part, accessible through another keyboard shortcut, for advanced settings like bus frequency divider, cas latency and so on. As soon as the device lost it's cmos ram content because the backup battery is removed, there's probably garbage in this area of the cmos ram and the bios does not handle it correctly - and only boots with turbo off. As soon as you write the default values once, the system works flawless at turbo speed. The behavior is reproducable by disconnecting mains and the backup battery.

Maybe this description helps others who suffer from similar issues.

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