Yup, it's almost certainly your RAM, the 4164-12 is rated at 120ns which translates to 8.333MHz. The 41256-10 is rated at 100ns which translates to 10MHz. In order to be stable at 12MHz, you'll need RAM that's rated at 80ns, something like a 41256-8. Check if your BIOS allows you to insert waitstates for your RAM (RAS/CAS etc), if it does, set the waitstates to the highest settings (ie highest numeral value, such as 5 instead of 4). If you get it working, you can then start experimenting with the values and start lowering them until you get the lowest values where your PC is still booting up and stable.

orcish75 wrote:

Yup, it's almost certainly your RAM, the 4164-12 is rated at 120ns which translates to 8.333MHz. The 41256-10 is rated at 100ns which translates to 10MHz. In order to be stable at 12MHz, you'll need RAM that's rated at 80ns, something like a 41256-8. Check if your BIOS allows you to insert waitstates for your RAM (RAS/CAS etc), if it does, set the waitstates to the highest settings (ie highest numeral value, such as 5 instead of 4). If you get it working, you can then start experimenting with the values and start lowering them until you get the lowest values where your PC is still booting up and stable.

Thank you again for your help, I really appreciate it. My board has a 10 MHz 286, it's just the Landmark 6.00 that shows ~12 MHz when I enable high speed. I've asked FoxBlack (administrator of the Moldavian oldpcmuseum.com site) to send me some pictures about his wotking motherboard, which is the same type as mine. He was kind and sent me pictures, and he also has the 41256-10 DRAMs and the 10 MHz CPU, so I suspect that my 4164-12 DRAMs are to blame.

About the wait states: the motherboard's manual tells that it's only possible to set the I/O wait states via a switch. I tried it already (by changing from 4 to 6), but that didn't solve my issue. I have to find some 41256-10 (or -08) DRAMs.

I think the board should have worked with the 512 KB of 41256-10 chips at 10 MHz for the first owner. Who might have extended the memory to 640K with the 4145-12 chips and it resulted the slowdown. Now, about 20 years later,I hope I will find the solution by getting the proper DRAM chips.

I will keep you informed about the results.

Thank you again for your help, I really appreciate it. My board has a 10 MHz 286, it's just the Landmark 6.00 that shows ~12 MHz when I enable high speed. I've asked FoxBlack (administrator of the Moldavian oldpcmuseum.com site) to send me some pictures about his wotking motherboard, which is the same type as mine. He was kind and sent me pictures, and he also has the 41256-10 DRAMs and the 10 MHz CPU, so I suspect that my 4164-12 DRAMs are to blame.

It's only a pleasure! Hopefully we'll get it running at 10MHz. There's a guy at Amibay selling some 41256-8 DRAMS if you're interested. Here's the link http://www.amibay.com/showthread.php?72726-DRAM-41256-80ns You should be able to expand it to 1MB if you fill your second bank with these chips.

Let me know if you have no luck with burning the XTIDE EPROMS, I send a couple over to you. 😀