Oscillator issue motherboard will not post 486 EISA \ VOGONS

Oscillator issue motherboard will not post 486 EISA

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First post, by Turboman

Posted on 2019-09-11, 18:26

Turboman Offline

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I have an Asus EISA-486SI motherboard I believe it is their first one or a early model. It has a 16MHZ oscillator and boots fine with the CPU showing at 16MHZ.
Under the oscillator socket it shows 20-50MHZ so far I have tried a 20, 33, 50, and 66MHZ oscillator and it will not post with any of them.
Am I doing something wrong? I thought just swapping out the oscillator would increase the MHZ of the CPU? I also made sure the jumpers are set correctly.
There is a jumper JP9 for <=33MHz or 50MHz

https://stason.org/TULARC/pc/motherboards/A/A … EISA-486SI.html

Reply 1 of 1, by Disruptor

Posted on 2019-09-11, 19:02

Disruptor Offline

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Posts: 1460
Joined: 2018-03-22, 18:31
Location: European Union

I've got an EISA motherboard that may not post when the clock divider in my BIOS results in a too high ISA bus frequency after changing the oscillator.

Try to set the ISA clock divider BEFORE changing the oscillator.

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