Simple assembly program not working on MSX 2
Welcome here, gzito! 
Use "CALL 00C3H" rather than "CALL 0849H". On an MSX1 (or at least some of those), this address (00C3h) jumps to the address you used. On an MSX2, this entry jumps to some other address, and at 0849h there will be code that does something else entirely. The 00C3h entry (CLS) is an official entry, guaranteed to do the same thing on different MSX models. 0849h is not, this could change randomly between models (as you found out). Where did you get this address anyway?
Also I suggest you put the BIOS addresses on top of your listing using EQU statements, using the names from official MSX bios documentation. That way your listing becomes much easier to read. And if for some reason you decide to use some other address for one of them, you only need to change 1 point in your source listing (vs. 3 here if for example you'd use something else for 00A2h). Same can be done for other constants.
Pro tip: I usually put the ORG after the BLOAD header.
For example like so:
CHPUT: EQU 00A2H CLS: EQU 00C3H CR: EQU 0DH LF: EQU 0AH DB 0FEH DW BEGIN,THEEND-1,BEGIN ORG 0E000H BEGIN: CALL CLS LD A,'A' NEXT: CALL CHPUT INC A CP 'Z'+1 JR NZ,NEXT LD A,CR CALL CHPUT LD A,LF CALL CHPUT RET THEEND: END
Where did you get this address anyway?
See book "Starting Machine Code On Msx" by G.P. Ridley, on page 78.
BTW I've found a lot of typos in it....
Anyway using official bios routines entry points is safer and also much more correct, you're right. Also using EQUs make code more readable.
I'm just playing again with Z80 assembly on MSX after 30+ years, I was about 13 years old when used Zen Assembler for the first time... Now I'm 47 and currently trying sjasmplus and asmsx cross compilers on Windows 10 
Congratulations to all the people behind the site.
I think MSX.org is really great !
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