User's Manual

Troubleshooting Testing for Power - 6
Testing DCO (Down Converter On) Voltage at C10 on the Logic
Board
In a No Power situation, first check for +5 V trickle power at J9
(refer to “Testing J9 for +5 V Trickle Power on the Logic
Board”), then check the DCO (Down Converter On) voltage on the
logic board at capacitor C10 (see figure below).
The DCO voltage should be present as soon as the power cord is
plugged into the computer. Ground the black probe on the volt
meter to the logic board screw, as shown in the photograph below.
Touch the red probe to C10 (see the photograph below.) The DCO
voltage should measure approximately -1.2 volts with the power
cord plug plugged in. The voltage will jump to 21 volts after pow-
ering on the system. A reading of -1.2 volts up to +1 volt indi-
cates the logic board is OK. Without a reading of -1.2 volts, verify
the fuse at F901 is OK (refer to “Testing the Power/Analog Board
Fuse” in this section). If the fuse is OK replace the power/analog/
video board.
Testing DCO Voltages at C10 on the Logic Board