You're probably mired in an L1 write-through vs. write-back or pinout difference issue.
Double check whether your DX4-100 is a plain or "enhanced" -- I assume it's enhanced.
Double check all jumper settings. You likely want the "P24D" aka 486DX2-66WB setting, except 3.3 volts instead of 5.

Thank you! My CPU is AM486 DX4-100 100SV8B

The MB does report jumpers for 100NV8T instead.

Jumper page is here - not much description unfortunately. https://theretroweb.com/motherboard/manual/ju … 7a793776395.pdf

Thanks for now!

Edit.

I see! So I shall set the CPU like P24D but the last three jumpers for 3.3V operations! Thanks I'll try that!

I tried with P24D - I can now boot with L1 cache enable - thank you!!

However, L1 is still not working. I can see from the benchmarks. there is no step at 8KB when reading.
CPU identification utility is telling me L1 is enabled in Write-THROUGH mode, but I thought it was supposed to be Write-BACK for my CPU? Have I made a mistake somewhere?

However, the TURBO button now works.

Thank you!

Not sure if the P24D jumper settings are fully compatible with DX4, even Intel WB-enhanced ones. Usually there are some differences.

You should set the jumpers for the AMD DX4-120SV8B (which is labeled 'DX4-120V8BS' in the jumper sheet), but keep the bus speed at 33MHz so it runs at 100MHz. The frequency should be the only difference between your CPU and the DX4-120, so all the other jumper settings would be the same as for any enhanced AMD DX4.

If that doesn't work, just try the settings for an Intel DX4-100. Unlike the NV8T, the Intel DX4 jumper settings are the same as for AMD Enhanced but you will get L1 in Write-through mode.

Amazing, thank you! I'll try ASAP.

It seems like DX4-120SV8B settings should be fine, but you have to find jumper combination for 33 MHz bus speed setting.

Will this be a part of some future video?

Yes, the frequency is selected by different jumpers and they are documented. The jumpers in the table are... unknown, I can only follow the list and hope. Except the last three, those are for voltages and are documented separately.

Of course there will be a video, I've mentioned this thread already! 😀 I can't wait to try!

Thanks!

Well, you know, it's a typical "486 jumper hell" 😀 Especially when there's no clear definition for each individual jumper in the manual, as in your case. At least you're lucky to have the voltage and frequency setting jumpers described. Your "359" and "259" yt-channels are among my favorite ones. Wish you luck with this mobo and CPU, and I'll be waiting for a longer video on your main channel.

It's a hell for sure!!!

IT WORKS!!! Thank you so much guys! The MB is cr$p though, after running a specific benchmarks, the CPU slows down (??) and to regain the full speed I need to power cycle. Was ASK a PC-Chips thing??
Thanks so much again, I needed to finish a video to feel better today!

And thanks for your kind words, @analog_programmer!

Great video tony359, so glad this board is working!

Here’s the video repair!

Vogons mentioned and this conversation is listed in the description!

Thanks all for the help!!

https://youtu.be/nY_BK2-m-0w

Hi Tony, great video as always!

Your DX4-100 seems to be a relabeled Am5x86-P75 due to its 16 KB of cache and package code 25544.
So you might want to look for the 2x/3x multiplier jumper on the motherboard and set it to 2x, which should make the CPU run at 133 MHz.

It would also be interesting to see a speed comparison with your VLB board at the same speed with a decent VLB video card.
Keep up the great work!

watson wrote on 2024-11-15, 19:17:

Your DX4-100 seems to be a relabeled Am5x86-P75 due to its 16 KB of cache and package code 25544.
So you might want to look for the 2x/3x multiplier jumper on the motherboard and set it to 2x, which should make the CPU run at 133 MHz.

Good catch about the CPU markings. Now go figure out which jumper combinations are responsible for CPU multiplier setting 😀

Yes, 16kB of L1 cache does indicate 5x86. That was the main difference in AMD's line up between fast 486 and 5x86.

Now go figure out which jumper combinations are responsible for CPU multiplier setting

I'll test on my other 486 MoBo, the SiS. The ASK is just impossible! 😁

Thanks for spotting that, it looks like it's a desirable CPU! So was that sold as 486 because AMD ran out of stock?

Yes, a strange marking/marketing issue. 😉

vswitchzero made a nice video about this.
https://www.youtube.com/watch?v=wm_QoqwQ1hU

Cheers, Jan

Yes BuB mentioned that video when mine was already live unfortunately. I haven't watched it, I'll take a look, thanks!