But SIO Drive Max doesn't work only with this motherboard !?

Why do you think SIO Drive Max load fail (boot error) ?

That's right, I've always been careful to put the RAM chips in the right way !

Have you tested base RAM with something more than a SELF-TEST? MT chips are known to go bad. Yes, I have the Jurgen's Sys-Check cartridge ! Interesting - you have 3 different types of capacitors in RAM BANK 1, and some sockets are rotated by 180°. Some sockets are rotated by 180° ? I don't understa...

I don't know if it helps but the 6502 is hot !

I replaced MMU and cross-wire its socket (64k native mode) like your screenshot, the same !
What can I try now ?

These "resistors" mounted instead of EMMU are just jumpers (0 Ohm). I want to be sure I have understood correctly before starting, in first (step 1) I remove MMU and cross-wire its socket like your screenshot. If that doesn't work I replace MMU (I own 800XL MMU) without modify step 1, tha...

Try to remove EMMU and cross-wire its socket, so the computer would behave as it had only 64 kB of RAM, and if it doesn't help, try to substitute MMU with another one or a GAL replacement (in 800 XL it was a PAL chip, so GAL replacement is 100% compatible). EMMU_64k.png Ok I try this, thanks ! No n...

tzok wrote: ↑Sat Dec 19, 2020 10:58 pm I prefer this test for extended RAM:
https://satantronic.com/files/8bit/tools/XRAM0220.XEX

Thanks, I tried it but it freezes on this screen :
After reset :
After power off/on and relaunch XRAM :
There are any points on basic screen, like a grid...

I just checked extended memory with short test :
Other problem, games don't launch with SIO/SDrive Max !

PS. I changed 6502 and ANTIC, the same...