Hello! I discovered some news during repairing some famiclones.
In most famiclones (especially MT-777DX) there is UA6527P as CPU and UA6538 as PPU (working @ 26.601712 MHz crystal). These chips looks like (a'ka NEW CPU
That is - they are dated from half of '90 to '94.
I bought some CPUs and PPUs for the replacement at aliexpress and they look different! The UMC logo is diffrent and the date is earlier - before half of '90, so they might be older revisions (a'ka OLD CPU):
Then I checked how some games works (Big Nose the Caveman, Micro Machines, Dizzy Adventurer, Asterix) on these consoles by replacing CPU/PPU and putting them in various combinations (old cpu & old ppu, old cpu & new ppu, new cpu & old ppu, new cpu & new ppu) and the results are amazing - the way they plays depends not on the PPU but on the CPU!
Now the results!
GAME | OLD CPU | NEW CPU
Ordinary Micro Machines (dated 1991) | Glitches | No glitches
Alladdin Micro Machines (dated 1992) | No glitches | Doesnt even start
Big Nose Freaks Out | Glitches | No glitches
Alladdin Big Nose Freaks Out | Glitches | No glitches
Dizzy Adventurer | Doesnt break when paused | Breaks when paused
1991 Micro Machines at new cpu:
Big Nose Freaks out at new cpu:
1991 Micro Machines at old cpu:
Big Nose Freaks out at old cpu:
Big nose freaks out on old cpu:
https://youtu.be/C1uyC0tGr8k?t=3m4sBig nose freaks out on new cpu:
https://youtu.be/C1uyC0tGr8k?t=12mSo if it is not because of ppu oam, have you got any ideas why the glitches?