kalohimal wrote on 2020-06-19, 14:38:

Any idea what's the likely problems? I kinda suspect corrupted ROM issues but unfortunately I do not have any UV-EPROM/flash with the correct size at the moment.

The first one:
Maybe there is a RAM- problem . So try to decrease amount of SIMMs and inspect wires near CMOS bat.
The second one:
Also inspect visually the board, the quality of soldering of big chips, double check jumper settings.
I would try to run system without RAM - will it beep error "no RAM" or will it stop at another POST code ?
The board has got ROM DIP32 socket, so I would try to understand where empty pins of ROM socket are connected. And then maybe a EEPROM 1Mbit chip (something like sst 29ee010 in DIP32 package) will work instead of UV 512kbit chip.

@Roman555

Thanks! Your suggestions prompted me to reread the manual... For 2nd board, I noticed in the manual that they did not mentioned whether the 72 pins SIMMs are FPM or EDO. My suspicion is it is FPM, since if they don't mention EDO it usually means FPM. Then I checked the Sis 471 datasheet, and woohoo it says FPM. I took out the EDO SIMM and replaced it with the only FPM stick that I have... progress! Now the post code is D4 instead of F0, ha. According to this doc on AMI website, D4 means "Test base 512KB memory. Adjust policies and cache first 8MB. Set stack. " So maybe my one and only FPM stick is bad? Or maybe the cache? Hmm... will need to investigate some more... to be continued 😁

Btw if no RAM is installed it will do the "RAM missing" long beep, and stop at post code D3. I look beneath the ROM socket and indeed the empty pins have traces going towards the SIMM sockets, so I guess they are connected and mybe can use larger flash (can't see exactly where they go as they are covered by the sockets). The manual said there is a jumper for selecting UV-EPROM or flash, and can be "normal or bootblock" flash, but never mentioned the size.

386 and 486 boards are FPM always. Not EDO. Pentium boards can use either but not both.

Cheers,

I think some newer 486s do support EDO. I have a Lucky Star LS-486 board that can take it. But yeah you're right that the older ones will only take FPM.

Unfortunately I have an entire stack of EDO but very limited FPM 🤣

And #2 is working now, so happy 😁 Turns out to be jumpers problem (these 486s have tons of jumpers and are a real PITA). There are 2 jumpers to select the "UMB function". The manual said:
"We have three kinds of Sis 471 MB to support 3.45V CPU.
First: with UMB on board and voltage autodetect.
Second: without UMB on board (and then explain how to set the jumpers).
Third: with UMB on board but without voltage autodetect (and then explain how to set the jumpers)."
It never explains what is "UMB" and how to identify the different type of boards though. The jumpers were removed (for 3.45V), so I just added them back (for 5V), and then it works. I bought this board new in the 90s and used it as my daily system, so I'm sure the jumpers were correct back then. Somewhere along I must have stolen these jumpers for another board, but never wrote them down 😁

Now time to scratch head on the first board.

Nice job getting that second board fixed. For the first board double check the jumpers for the cache size are correctly set and you can also try removing the cache chips and seeing if it'll boot.

kalohimal wrote on 2020-06-21, 02:39:

I think some newer 486s do support EDO. I have a Lucky Star LS-486 board that can take it. But yeah you're right that the older ones will only take FPM.

Unfortunately I have an entire stack of EDO but very limited FPM 🤣

ls.jpg

Some things are so obvious that I don't remember to mention them 😀 LS-486 supports EDO only if it has the latest revision of the chipset. Also the latest UMC based boards support EDO. And if you have so many EDO sticks there's a trick (need soldering iron) to make some of them work on boards that supports only FPM.
I'm glad you've sorted out and the board is working now.
P.S. What about UMB - the manual maybe referres to Upper Memory Blocks
https://en.m.wikipedia.org/wiki/Upper_memory_area