I had this 350-in-1 multicart:
It does not work at all in most of my famiclones, except one, on which it starts without problems on 8/10 powerups, on 1/10 it has glitched menu graphics and on 1/10 some random game is started instead of menu.
I suspected reset circuit to be cause of problems and examined signals on them - indeed, reset, fed to latches is oscillating (version with 74LS02). I replaced the gate with different LS02 chip but same result - and I tested both gates on logic tester and they are OK. The interval of oscillations is 50 Hz (20ms) so probably some noise from mains.
Then I replaced LS02 with HC02 and it works fine:
Any idea what is cause of troubles? Does thus LS gate have some kind of retardance when sourcing surrent?
It does not work at all in most of my famiclones, except one, on which it starts without problems on 8/10 powerups, on 1/10 it has glitched menu graphics and on 1/10 some random game is started instead of menu.
I suspected reset circuit to be cause of problems and examined signals on them - indeed, reset, fed to latches is oscillating (version with 74LS02). I replaced the gate with different LS02 chip but same result - and I tested both gates on logic tester and they are OK. The interval of oscillations is 50 Hz (20ms) so probably some noise from mains.
Then I replaced LS02 with HC02 and it works fine:
Any idea what is cause of troubles? Does thus LS gate have some kind of retardance when sourcing surrent?