Hi there Got a Diamond Flower (DFI) 486-25/33/50 ISA motherboard, all works great! Massive retro AT motherboard in it's original DFI case. Sorted out the clock issue

It originally came with a 486sx 25Mhz processor so I have removed it and put in a 486dx 33Mhz processor. It starts up fine and shows up as a 486dx 25Mhz as expected. But I am having trouble trying to change the speed of the CPU to 33 Mhz. My motherboard looks exactly like this diagram.

http://open-sez.me/th99/m/C-D/31405.htm This is the closest I can find as this one is a 486SX-16/20/25UCE

When I set J7 can set the speed between 12.5 MHz and 25 MHz and that's it'. I've played with J4 and J6 despite them being factory jumpers it made no difference.

All other jumpers are for the cache memory which are set correctly at 128KB cache and the other one for the colour/mono monitor selection, the only one I have not touched is J19 but I doubt it's that.

I just wondering if I'm doing something wrong or something i'm just not seeing. Any ideas?