Sun Microsystems SPARCclassic Service Manual page 144

c. Using a Volt-Ohmmeter (VOM), measure the power supply voltages at the
Caution -
harness is not connected to the main logic board. Without load, the power supply
will not regulate.
4 Red: +5V
4 Blue: +12V
4 Brown: -12V
4 Gray: POR (Power on reset)
4 Black: Ground
Note -
and pull up is on the main logic board.
The limits for the voltages are:
4 +5V: 4.90 to 5.10
4 +12V: 11.16 to 12.84
4 -12V: -11.6 to -13.2 with a hard drive
4 -12V: -10.2 to -13.8 without a hard drive
If the voltages are correct, you can rule out a defective power supply.
1. Reconnect the cables and SBus cards one at a time and measure the voltages
2. Close the system unit using the procedure in "Closing the System Unit" on
3. Enter the Forth Toolkit.
a. Turn on the system and the terminal. The system will start to boot.
b. Interrupt the boot sequence by pressing the Break key on the terminal
c. If you see the ok prompt, go to step 3-e. If you see the > prompt, continue
SPARCclassic/SPARCclassic X/SPARCstation LX Service Manual ♦ Revision A, November 1993
130
12-pin power connector on the main logic board.
Voltage measurements will be inaccurate if the power supply wiring
The colored wires of the power harness supply the following signals and
voltages:
The POR signal is a Transistor-Transistor Logic (TTL) open collector
each time. In this way, you can determine whether one of the system
components is holding down a power supply voltage.
page 55.
keyboard.
with step 3-d.