Soltek SL-75drv4 (via KT266A) can't see Duron 1400 (Applebred)

I changed CPU on SL-75drv4 to Duron 1400(Applebred)FSB 133Mhz.
Motherboard can not see new CPU. Duron is OK, it is working on Asus
A7n8x correctly. Soltek with former CPU (Athlon 1700+), also runs OK.
Changing FSB to 100Mhz did not help
I upgraded BIOS, no effect.
SL 75drv4 is 2 years old. Duron is with new core - is this the
problem?

thx in advance
corwin