TECH: Wizards of Wor : No game - reset line 0/5vdc
et...@757.org
I just bought a Wizard of Wor machine that I am working to get
running again. Previous owner said it was working, then one day it
never worked again.
The game has the original linear power supply, and all voltages are
correct. The monitor fires up, and when power is disconnected to the
game it flashes white.
I think I've narrowed down the issue. With the CPU card seated, the
reset wire from the power supply jumps between 0 and 5vdc, in a cycle.
With the card pulled, the power holds steady at 5vdc. I'm not quite
sure what the reset line does. Looking at the schematic on the power
supply side, it appears to go to 5vdc when power is good? Is this
correct? Then on the CPU card it is tied to the reset line on the z80,
which should restart the CPU. The watchdog also seems to be tied to it.
I already swapped out the 4401 transistor (Q10) that ties to the
reset line. Haven't switched out any 339's yet.
Further looking at the schematics, I might guess that the transistor
is used by the watchdog to reset the CPU, and the problem is elsewhere.
Does anyone have any insight into the watchdog/reset lines in the
gorf/wizard of wor machines? Care to shed some light? With the cardcage
design, it is impossible to really poke around the board with it
powered. TIA!