AMD DX4-100 running at 3x 50Mhz

AMD DX4-100 running at 3x 50Mhz - why ?

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First post, by Omarkoman

Posted on 2025-06-02, 08:21

Omarkoman Offline

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I have this motherboard:

AMI SUPER VOYAGER VLB-III

https://theretroweb.com/motherboards/s/ami-su … b-iii-s707#docs

and want to run AMD DX4-100 Mhz cpu in it.

I have setup the jumpers as per manual :

I have set the VESA speed ( see above manual) to 33Mhz as my understanding is the cpu is 3x 33Mhz and I also set the CPU type to 3x (if I set it to 2x or 2.5x PC wont post) - jumpers J19, J37, J43, J54 in top table.

The system posts however, running cpu check its reporting its running at 150Mhz 3x50Mhz

It posts fine, runs games and benchmarks ok so not sure what to do. Leave it as is (I have active cooling on it) or do I need to change anything ?

Keen to get some thoughts please. Thanks in advance.

Reply 1 of 11, by GigAHerZ

Posted on 2025-06-02, 08:39

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The FSB speed is probably part of the "CPU selection" jumpers. The VESA/VLB speed is not really speed. If you set it marked as "over 33MHz", it adds waitstates to the VLB communication so that cards designed for up to 33MHz speed could keep up. The FSB itself is set as part of the CPU jumpers. Too bad the manual doesn't specify which of those jumpers is about the FSB...

"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!
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Reply 2 of 11, by Omarkoman

Posted on 2025-06-02, 09:58

Omarkoman Offline

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Mystery continues, found this option in bios. Allows to change between 33/50mhz for dx4

https://i.postimg.cc/NYfBW703/IMG-2577.jpg

Issue is, when set to 50mhz, system boots. When set to 33mhz, the system hangs after post.

Reply 3 of 11, by GigAHerZ

Posted on 2025-06-02, 10:49

GigAHerZ Offline

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My thoughts would go on an idea that this 33/50 MHz switch in bios is really some kind of crystal selector - it would switch between 2 different crystals. It only assumes one crystal is for 33 and other for 50 MHz speed. (Maybe doubled to 66 and 100MHz on crystal itself)

But your board doesn't seem to have a "direct" crystal for the FSB/CPU... Not even one. (by pictures)

"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!
A little about software engineering: https://byteaether.github.io/

Reply 4 of 11, by Omarkoman

Posted on 2025-06-02, 11:15

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Yes, very strange. Its a fairly modern 486 board so no oscilators.

Reply 5 of 11, by Omarkoman

Posted on 2025-06-02, 22:24

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any other thoughts from anyone else ?

Reply 6 of 11, by Matth79

Posted on 2025-06-02, 22:37

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https://theretroweb.com/motherboard/manual/su … 60286615469.pdf Page 102 mentions specific settings, not sure if J12 is mentioned anywhere else. J37 also varies, that is definitely the 2x/3x multiplier select

Reply 7 of 11, by Omarkoman

Posted on 2025-06-02, 22:47

Omarkoman Offline

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ooh ! great find ! thank you !

when I set the J32 on 1-2 it wont post but I now need to check the J11, 12 and 15 which I dont think I touched. This should get it going at 2x50mhz.

I will have a go and report back.

Reply 8 of 11, by Omarkoman

Posted on 2025-06-03, 07:42

Omarkoman Offline

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Unfortunately i already has the jumpers the right way and 11,12 and 15 are free.

If i change the multiplier to anything but 3x (eg shorting pins on 37) , it posts but freezes on next screen.

https://i.postimg.cc/1yfmC2Q7/IMG-2599.jpg

Not sure what else to try or leave and run it at 150mhz

Reply 9 of 11, by butjer1010

Posted on 2025-06-03, 08:26

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This CPU normally works on 33MHz x 3. So JP37 needs to be open. On page 92 it says J12 needs to be shorten for 33x3, and open for 2x50. Maybe this is the problem. Please try and let us know...

Reply 10 of 11, by Omarkoman

Posted on 2025-06-03, 09:19

Omarkoman Offline

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Omg that worked!!! Thank you!!!!

Reply 11 of 11, by butjer1010

Posted on 2025-06-03, 10:51

butjer1010 Offline

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Omarkoman wrote on 2025-06-03, 09:19:

Omg that worked!!! Thank you!!!!

Yessss, that is what i want to hear!!!! Great news!!!

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