Sun Microsystems SPARCstation 20, Service Manual

Page: 53 / 266

Chapter 4 Troubleshooting Procedures 29
5. If the monitor power supply is internally fused, check the fuse.
Power-On Does Not Succeed
To check for a power-on failure:
1. Remove the DC power from the system by pushing the back panel power switch
to the standby position.
2. Check that the power cord is properly connected to the system back panel power
receptacle and to the wall outlet.
Caution – This equipment contains lethal voltage. Accidental contact can result in
serious injury or death.
3. Using a VOM, verify that the wall outlet is supplying AC power to the system.
4. Restore DC power to the system. Press the back panel power switch to ON and
observe the keyboard.
The keyboard LEDs should briefly light. An audible tone from the keyboard should
be heard.
■
If no tone is heard or if no lights are seen, the power supply may be defective. See
“Power Supply Test” on page 29.
■
If a tone is heard and lights are seen, but the system still fails to initialize, see
“System Board Test” on page 31.
Power Supply Test
To test the power supply:
1. Using a VOM, check the output voltages of the power supply (
FIGURE 4-1
,
FIGURE 4-2
, and
TABLE 4-2
).
Place the VOM negative probe on one of the logic ground pins in the connector and
test the +12V, –12V, and +5V power pins individually with the positive probe (pins 1
through 8).
Note –
The power supply connector must remain connected to the system board
during this test. This allows the power supply to regulate the voltage.