I've just had a strange RAM behavior on 486 VLB motherboard.
It's ECS UM486V rev. 2.0 motherboard that has 8 30-pin connectors for memory. Specially for that case I bought 8 sticks of 1MB SIMM30. 4MB SIMMs are hard to find and expensive. All of these RAM modules have 3 ICs on them but from different manufactures.
The seller gave me 16 modules in total to check all of them.
8x1 MB Fujitsu chips (2x70 ns, 1x60 ns parity)
4x1 MB TI Chips (2x70 ns, 1x70 ns parity)
4x1 MB TI Chips with third parity chip having AM marking (all three are 70ns).
TI/AM chips caused Parity errors on different stages of loading process, seems like all of them caused problems as I tried them in different combinations.
Fujitsu and TI modules are working great BUT only 4 of them. When I install 8 modules the computers sees only 4 MBs of RAM. I tried all possible combinations and that's definitely not a RAM problem.
I found a solution for that. I have a 386 m/b with 4x1MB GoldStar modules installed. They all are 9 chips and 80 ns. I took these 4 modules and put them to the second bank and it worked! I'll play with it more, now I have plenty of combinations as I don't understand what causes that - amount of ICs of IC timings but at least I don't have to search for other RAM chips.
486: ECS UM486 VLB, 256kb cache, i486 DX2/66, 8MB RAM, Trident TGUI9440AGi VLB 1MB, Pro Audio Spectrum 16, FDD 3.5, ZIP 100 ATA
PII: Asus P2B, Pentium II 400MHz, 512MB RAM, Trident 9750 AGP 4MB (Voodoo2 SLI, MonsterSound MX300 in plans)