Compaq AlphaStation XP1000 Power Troubleshooting

Power Supply

The 400-Watt power supply provides six regulated outputs to the system:

+3.3V
+5.0V
+12.0V
-5.0V
-12.0V
+5VAUX

(See Power Supply Pinouts). The supply has overvoltage protection on +5V and +3.3V, and overcurrent protection on all outputs. There is an output signal, POK_H (DCOK), with 1ms warning for power up and power down. The power supply contains one 80-mm DC fan.

Note: When powering off the system, ensure that it remains off for at least 45 seconds before you reapply power.

Alpha 21264 Processor DC-DC Converter

The Alpha 21264 processor requires a power supply voltage (VDD) of 2.2V. The VDD current is expected to exceed 50A (the Alpha 21264 = 666MHz) with a dI/dt requirement that is approximately 15A/usec. This voltage is derived from a DC-DC converter (the EV633 Regulator) that operates off the 5.0V output from the bulk supply and also provides load regulation through a switched regulator. The EV633 Regulator is located on the MLB very close to the CPU Daughter Card connector. The 2.x V power is bussed through the CPU Card connector through enough pins to accomodate in excess of 50A and provide a low inductance path to accomodate the fast di/dt requirements.

The main features of the EV633 Regulator are listed below:

Programmable Outputs from 1.429V to 2.5V in 71mV steps via a 4 bit code. This code is driven from the CPU Daughter Card via 4 pins.
Output current rating of 55A
4.5-5.25V input
Overvoltage and overcurrent protection
thermal protection
Reg_OK and Over_Temp signals. These signals are used by the power up and interrupt circuitry on the MLB. Reg_OK is used for DCOK generation and Over_Temp is used to interrupt the CPU.

Troubleshooting Suggestions

Symptom	Check
Power indicator is OFF.	Front-panel power switch was not pressed. Power at wall receptacle. AC cord.
Power indicator is ON for a few seconds and then goes OFF.	There are three fans in the Compaq AlphaStation XP1000 System: two are at the front of the system (top and bottom), and one is in the power supply. CAUTION: The power supply shuts OFF within 1 second if its internal fan fails.
Power indicator is ON, and the display monitor is blank.	Monitor power indicator is ON. Raster present if brightness is turned up. Fuses and circuit breakers. Video controller cable is properly connected. Power is present at system board.

Power Supply Pinouts

Power Supply Connector	Pin Number	Wire Color	Voltage
P10 and P11 Disk Drives	1 2 3 4	Red Black Black Blue	+5V Common Common +12V
P12, P13, P14, P15, and P16 Disk Drives	1 2 3 4	Blue Black Black Red	+12V Common Common +5V
P1 MLB	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20	Brown Brown Black Red Black Red Black White Purple Blue Brown Yellow Black Green Black Black Black Gray Red Red	+3.3V Sense +3.3V Common +5V Common +5V Common POK_H +5VSB +12V +3.3V -12V Common DC_ENABLE Common Common Common -5V +5V +5V Sense
P2 MLB	1 2 3 4 5 6 7 8 9 10	Green Black Black Brown Brown Green Black Red Red Red	Jumper (to pin 6) Common Common +3.3V +3.3V Jumper (to pin 1) Common +5V +5V +5V
P3 MLB	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24	Black Black Black Black Black Black Black Black Black Black Black Black Red Red Red Red Brown Brown Brown Brown Brown Brown Brown Brown	GND GND GND GND GND GND GND GND GND GND GND GND +5V +5V +5V +5V +3.3V +3.3V +3.3V +3.3V +3.3V +3.3V +3.3V +3.3V