feipoa wrote on 2020-03-24, 09:11:

ychh0, what motherboard are you using? If it is an M919, 'nuff said. I have two of those boards and they are incredibly buggy.

At first I missed his MB description too:

My 486 mainboard is made by SAMSUNG with Pheonix bios and officially support up to PODP83 with Bios upgrade. This mainboard has 4 ram sockets each accept 16MB single sided 72pin EDO ram total 64MB, and equipped with 256KB L2 cache. I upgraded CPU with Intel 486DX4-100Mhz (tried AMD 5x86 133MHz and PODP 83MHz but unstable, lag and so on) and installed adaptec AHA 1542CP with SCSI2SD v6 (tried AHA 2842A but system does not post). And I installed Bootit Bare Metal for OS multi boot.

Otherwise I have good experiences with M919 V3.4B/F. I have other earlier revisions too but haven't used/tested them much.

I don't know of any 486 motherboard made by Samsung. Is there a photo of this board?

feipoa wrote on 2020-03-24, 09:11:

ychh0, what motherboard are you using? If it is an M919, 'nuff said. I have two of those boards and they are incredibly buggy.

My mainboard is made by SAMSUNG in mid 1990’s . It’s with Pheonix bios which has little parameters that users can control . I feel this mainboard is not so trustworthy there may be possibility of mainboard bug related with this problem. Or there is possibility it has some defective parts - it’s already more than 25 years old one.
I checked power supply and it’s output voltages are normal and the VLB card and ram also seems to be no problem. Therefore I suspect mainboard incompatibility( bug) or some defective part of it.

If you want 64 MB, try using two single-sided sticks of 60 ns, 32 MB FPM. If fails, try double-sided.

feipoa wrote on 2020-03-25, 19:01:

If you want 64 MB, try using two single-sided sticks of 60 ns, 32 MB FPM. If fails, try double-sided.

This mainboard does not recognize double sided ram. I looked around and there seems no 32MB 72pin single-sided one, instead I would test one 64MB module though I doubt this mainboard recognizes it.
The pictures of Samsung mainboard and PC are attached as follows.

How many different double-sided sticks did you try? Some old boards don't like certain RAM brands. I too only have 16 MB and 64 MB in single-sided FPM.

Interesting looking board. I've never run across one of these. Are those DIP sockets for more cache? I'd suggest upgrading the SRAM cache. The upgrade hopefully allows for for double-banked interleaved mode, which allows for faster memory and cache timings.

I assume you have the i486SX disabled, probably via those nice DIP switches

feipoa wrote on 2020-03-26, 07:09:

How many different double-sided sticks did you try? Some old boards don't like certain RAM brands. I too only have 16 MB and 64 MB in single-sided FPM.

Interesting looking board. I've never run across one of these. Are those DIP sockets for more cache? I'd suggest upgrading the SRAM cache. The upgrade hopefully allows for for double-banked interleaved mode, which allows for faster memory and cache timings.

I assume you have the i486SX disabled, probably via those nice DIP switches

I tried several double sided rams and other users also say the same. It should be the mainboard inherent design.

DIP switches are used for settings. CPU type, clock speed, VESA clock speed, VESA wait timing, L2 cache, hibernation and so on. There are 4 boxes of DIP switch.

There were several lines of this model released depending on CPU type, L2 cache size and so on. Mine is top grade line with 486DX2-66MHz, 256kB L2 cache. The one in the picture is probably mid-low grade one, with 486SX and 128kB L2 cache. Yes the socket is for the additional 128kB cache memory.