Always Check Diode D17: Checking the Battery Voltage and D17 Diode.
I find the blocking diode D17 should be checked on all system3-7 CPU boards. This diode prevents the +5 volts rail from trying to charge the AA batteries when the game is on, and also from trying to power the whole CPU board when the game is off (instead of just the 5101 RAM chip). I find this diode bad quite often (about 20% of the time), especially on system6 CPU boards. On the non-banded side of diode D17, the battery voltage in reference to ground should be about 4.4 to 4.8 volts DC. On the banded side of diode D17, it should be about .5 volt less, or 3.9 to 4.3 volts DC.
If there is no voltage on the banded side of D17, but there is voltage on the non-banded side, replace this diode with a new 1N4148 or 1N914 diode. If there is no voltage on the non-banded side of diode D17, then the batteries or battery holder is at fault.
Mer info her:
http://www.marvin3m.com/sys37/index1.htm#batteryHåper det hjelper
:-)
