Network Server Hardware Troubleshooting Guide:
Symptoms and Repair Flow

Table of Contents


The target end user for this document is a hypothetical well-trained service engineer whose job it is to diagnose and repair a Network Server system. The procedural flows described in this document are not meant for maximum customer uptime, they are meant for maximum discoverability of problems and least cost of repair. Therefore, they may or may not suit a given situation. However, the information in this document can very likely be adapted to the specific needs of service, factory, or on-site personnel. Such adaptation is left to the various Directly Responsible Individuals.

Causes are in listed order of probability and diagnosis. A high-level troubleshooting strategy is described. Note that when a part is removed or replaced in any repair flow it is assumed that the unit is put back together into a power-on state, with the rear keyswitch locked and the Main Logic Board fully seated. Note that top or side panels do not have to be re-installed to re-power the unit, however hazardous voltages may exist and all normal precautions are advised.

All Part Numbers refer to the Service Part Number.

I. Normal Startup and AIX Boot on the Network Server

Suppose you walk up to a Network Server and hit the front power switch. What is the chain of events that results in a Unix Login prompt? First and most important, an AC path must exist to the unit's power supply. This means that the unit is plugged in, the AC line filter 922-2088 is working, the AC interlock switch (no Service Part Number ?) is closed by virtue of the Main Logic Board being fully seated, and the power supply is installed correctly.

Second, a DC path must exist between the power supply and the Main Logic Board. This means that the Power Cable must be correctly wired and installed, and the power supply must be supplying a Trickle voltage (+5 Volts) to the Power Controller IC (Cuda). Third, a logical and physical path must exist from the front panel switch (or keyboard power switch) to the Power Controller. This means that the rear keyswitch must be in the locked position, the Processor Card is fully seated (or fully removed, for debug purposes), Cuda must be in the proper idle state, and the cables and connectors to the power switch must all be in working order. If these conditions exist, power on will be successful. However, a quick shut-down could occur at this point if a short circuit exists, because the power supplies detect short circuits and automatically shut down to prevent hard failure. Also, the +5 volt line is monitored by the power monitor IC on the Main Logic Board and if the voltage is below +4.7 the unit will also be shut down.

Once valid power is applied to the Main Logic Board, the processor will execute instruction fetches from the system ROM (housed in a removable DIMM). The first software procedures in the ROM are called Power-On-Self-Test (POST). It is the job of POST to initialize the hardware into a working state, and establish a software path to the LCD. The LCD will then be written with progress reports on the state of the discovered hardware: DRAM, SRAM Cache, and various fan, temperature, and power supply fail states. DRAM will be sized, tested (but not exhaustively), and finally control will be turned over from POST to Open Firmware.

It is the primary job of Open Firmware to find a bootable device (CD, floppy, or Hard Disk) based on the device or devices listed in the boot path and the position of the front panel keyswitch. Open Firmware builds what is known as a device tree, which identifies the hardware configuration to the Operating System to be booted. The Operating System will interact with Open Firmware to pass device tree information, and eventually to set the default boot path in the system's non-volatile RAM, so that once a hard disk is installed with AIX, a user never has to interact with Open Firmware to boot the machine. On a Network Server that has never been booted before, if Open Firmware detects the key in the service position, it will attempt to find a diagnostic floppy or Install CD to boot from automatically. This allows the typical user never to have to interact with Open Firmware.

In order to find the bootable device, virtually the whole Main Logic Board, the Mezzanine Interconnect board, SCSI Cables, SCSI device, and SCSI backplane all need to be properly functional. If this is the case, Open Firmware can find the boot blocks on the bootable device. "Bootapple" messages are written to the screen, and a compressed "bosboot" image is loaded from disk into DRAM, expanded, and jumped to to begin AIX execution. At this point, the AIX kernel has been launched. Next, various configuration methods are run, SCSI buses are walked to discover attached devices, file server mode(auto-on) is turned on, the system QUACK is heard, and the first system wide interrupts are taken. (Open Firmware does not use interrupt based I/O processing). Finally, a File System Check (fsck) is performed, ethernet is configured, eventually nameservers are queried, various daemons are started, and usually the COSE desktop is launched. (The exact list of services, utilities, daemons and applications launched may vary based on what is configured in system boot files such as /etc/inittab and /etc/rc.)

Now that we understand how the Network Server launches AIX, we are better prepared to understand how failures to boot can be diagnosed. Each heading in the following discussion will introduce a major symptom.

II. No Power at All

Problem: Unit will not power on via the front panel momentary switch.

Probable causes: Unit not plugged in, rear keyswitch not locked, Main Logic Board or Processor Card not fully seated, hardware problem.

Troubleshooting strategy is to verify power-on conditions are met for the machine, then isolate other hardware causes.
  1. Unit is not plugged in to a live AC outlet. Verify. If still fail THEN

  2. Unit does not have the rear key switch all the way in the locked position (triple check this!) If still fail THEN

  3. Logic Module or Processor Card is not fully seated into the unit. Inspect the seating of the Processor Card ensuring that no gold fingers are visible where it mates into its connector. Then reseat the Logic Module, carefully and fully tightening the four thumbscrews and putting the rear keyswitch fully into the locked position. If still fail THEN

  4. Plug keyboard into ADB port and press power on key. If still No Power THEN go to 5. If power on successful go to 4a.

    a) See if machine will power down from the front panel power switch. If it does, congratulations, it's fixed. Otherwise, you've isolated to the interconnect system containing the NMI/Reset-PowerBd, the SwitchCable, the Mezzanine, and the Main Logic Module. Check and/or replace cable connecting momentary switch 922-2086. Retest. If fail then check or replace Interconnect Mez Bd. 922-2079. If fail then replace NMI/Reset Power Bd. 922-2081. If fail then replace Main Logic Module.

  5. NS 700 Only: Make sure Power Supply , 661-1131, is fully seated. If fail or NS 500 THEN

  6. Reset Cuda Chip (power controller IC) by pressing the red switch in the upper left hand corner of the Main Logic Module. Reseat everything firmly, making sure thumbscrews are tight and the rear key switch is in the locked position. (NOTE: Any time you execute step 6 the unit will lose its system date and time. When fixed the system date and time should be reset. If still fail THEN

  7. Unplug unit and verify AC wiring by removing the Left Duct 922-2124. If all wires are seated properly then replace Power Cable 922-2090 or Power Supply 661-1131 or NS 500 power supply. If still fail THEN

  8. Replace Main Logic Board.

III. Intermittent Power

Problem: Unit powers on but shuts down immediately. Front panel LED, and LCD flash on momentarily.

Probable cause: Unit has a short circuit.

Troubleshooting strategy is to isolate parts of the powered system until the short circuit goes away, then narrow it down to the failing replaceable unit.
  1. First verify the problem. If a user pushes the momentary power button and holds it for too long, the unit will shut down normally because the power controller IC is interpreting the holding down as a power-down request. If the problem is genuine, isolate the short ciruit by removing all SCSI devices from their seated positions. If still fail THEN go to 2. If unit now powers on, isolate to the shorting SCSI device. Once found, unplug the power to the SCSI device 922-2097 and retest. If still fail THEN unplug LED Cable 922-2098. If still fail THEN replace Drive board either Wide 922-2083 or Narrow 922-2082.

  2. Remove the power connector to the SCSI Backplane. If unit now powers on, replace SCSI Backplane 922-2080. If still shut down immediately THEN

  3. Remove (do not replace) the processor card 661-1126. If unit still shuts down THEN go to 4. If unit powers on, replace with a known good processor card and retest. If unit fails with known good processor card THEN go to 5. If unit powers on with known good Processor card, replace processor card.

  4. Remove DRAM, CACHE, and ROM DIMMS and retest. If unit still shuts down THEN go to 5. If now powers on, fault isolate to failing DIMM.

  5. Replace power supply (NS 700 use known good Power Supply Module). If fail THEN

  6. Replace Main Logic Board. NS 700 only, if still fail replace Power Backplane 922 2089.

IV. No LCD Display

Problem: Unit powers on but LCD does not display anything or displays incomplete or incorrect information.

Probable causes: LCD cable loose, bad LCD, system hardware failure.

Troubleshooting strategy is to first verify cables, then isolate to possible hardware causes.
  1. Make sure a monitor is attached. If unit does not launch Open Firmware to the monitor and/or boot CD or Hard Drive, go to V. No Open Firmware Launch.

  2. Remove Front Bezel 922-2111 and reseat both ends of LCD cable 922-2087. If still fail THEN

  3. Reseat Main Logic Board. If still fail THEN

  4. Remove Top Cover 922-2108 and ensure cabling from Interconnect Mez Board 922-2079 to Top Shelf connector is secure. Do not replace Top Cover and verify mating of Main Logic Board to Interconnect Mez Board. If still fail THEN

  5. Replace LCD and/or associated cables. If still fail THEN

  6. Unit has faulty path to LCD. Replace Main Logic Board

V. No Open Firmware Launch

Problem: Unit writes information to the LCD but does not launch Open Firmware.

Probable causes: Power-On-Self-Test didn't complete; NVRAM has been corrupted; system hardware failure.

Troubleshooting strategy is to reset NVRAM; then attempt to isolate possible hardware causes.
  1. Make sure unit is able to complete Power-On-Self-Test. If it has, the LCD will display the processor speed, the amount of DRAM, and the size of the L2 Cache. If LCD has only partial information go to 8.

  2. Make sure user has not redirected Open Firmware output to the serial port. If it is suspected that they have, attach an appropriate terminal to the appropriate port. If not, THEN

  3. Reset NVRAM by placing the front key in service position, restarting, and after the Long DRAM test is reported as begun on the LCD, typing CMD-OPTION-p-r simultaneously on an attached keyboard. Unit will lose its boot path and Open Firmware security password. Once the machine is booting, these will need to be reset to the correct values. See section VI. No Bootapple, item 11. If still fail THEN

  4. Slide the Main Logic Board out from the unit, and remove the battery for at least 3 minutes, Make sure there are no external devices other than a keyboard attached to the Main Logic Board. Reseat the battery and reseat the Main Logic Board, and reconnect the monitor. Unit will lose system date and time as well as any boot path and Open Firmware security password. Once the machine is booting, this will need to be reset to the correct values. See section VI. No Bootapple, item 11. If still fail THEN

  5. Unit has system hardware failure. Remove Cache and all but one Memory DIMM. If launch to Open Firmware, isolate to failing Cache or Memory. If still fail THEN

  6. Replace Processor card with known good. If still fail THEN

  7. Replace Main Logic Board

  8. Unit's LCD displays partial information: If the Long DRAM test does not complete, the number dashes (hyphens) found on the screen indicates the offending DRAM DIMM as shown in the following table. Please note that with 64 and 128Meg DRAM DIMM technology, it may take a minute or more for each dash to proceed along line 4 of the LCD display.

    # of dashes on LCD line 4 Offending DIMM DRAM slot 1 Logic Board DRAM
    (not implemented) 2 Logic Board DRAM (not implemented) 3 1A 4 1B 5 1A 6
    1B 7 2A 8 2B 9 2A 10 2B 11 3A 12 3B 13 3A 14 3B 15 4A 16 4B 17 4A 18 4B.
8a) Unit displays error message on LCD: The following are POST error messages and the appropriate action to take when encountered.

a) 'CudaNotResponding!!!' POST is expecting the Cuda chip to be idle, if it isn't this will be the message. First, attempt to power the machine down, and pull the AC plug for a minimum of 30 seconds. Replug the unit and try the front panel switch again as often this will make Cuda enter the idle state. If still fail, then use the red button on the Main Logic Board to force Cuda into the idle state. This will reset the system date and time. If still fail then remove the battery, following the procedure of item 4 above.

b) 'ParityAddrAtAddrFail' Probable DRAM problem, this has been seen when using a DRAM DIMM socket for the first time. The solution is to remove the new DIMMs from their sockets and re-seat them to work-in the socket. Check also for unqualified third party non-parity DRAM DIMMS.

c) 'Jumping to RAM prog.' If this is seen on the LCD and the system does not boot (more than once), this is an indication that the NVRAM soldered to the motherboard has failed. Follow the procedure of 4) above.

d) 'Drive Fan Failed!' The drive fan is the indicated field replaceable unit. If it is spinning see section X. Some Common Reassembly Problems below.

e) 'Processor Fan Failed' The Processor fan is the indicated field replaceable unit, see X. Some Common Reassembly Problems below.

f) 'Temperature Too Hot!' Processor Card is indicating an overtemperature. The AIX error report should have forewarned of this. Verify cooling paths are not obstructed.

g) 'Temperature Warning!' Processor Card is indicating an overtemperature. The AIX error report should have forewarned of this. Verify cooling paths are not obstructed.

h) 'Left Power Fail!' Power Supply is the indicated field replaceable unit.

i) 'Right Power Fail!' Power Supply is the indicated field replaceable unit.

j) 'Left Power Hot!' Power Supply is the indicated field replaceable unit; first verify cooling paths are not obstructed

k) 'Right Power Hot!' Power Supply is the indicated field replaceable unit; first verify cooling paths are not obstructed.

l) Unit's LCD displays correct information but then becomes a jumbled mess of letters. This indicates a Cache DIMM problem. Remove ; if still fail THEN go to 6.

m) Unit reports 0000Kbytes cache. User is using memory from an unqualified source. Any DRAM in the Network Server must not use ACT buffer technology, this causes incorrect configuration information to be loaded at system reset time. Check DIMM's for ACT buffers, usually 74ACT16244. FCT is the preferred technology.

VI. No BootApple

Problem: Unit launches Open Firmware, Open firmware does not respond on the monitor with a set of "bootapple" messages which indicate the successful loading of a boot image from a hard drive (or CD). Instead, Open Firmware prompt "o >" or "security> " is displayed.

Probable cause: No valid boot blocks found at the boot path.
  1. Troubleshooting strategy is to isolate the problem to an incorrect boot path, a bad CD drive, or a bad connection to the backplane port.

  2. If booting for the first time to the AIX Install CD, make sure the key is in the service postion and the install CD is in the(closed) CD tray. Restart. If AIX has already been installed ona hard drive, and/or the machine has lost the boot path because the battery was removed go to 11.

  3. Verify Open Firmware can see the keyswitch in the service mode by typing ".keyswitch" You need to log in if "security>" is the prompt, using the AIX root password. If not known, you must reset NVRAM by placing the keyswitch in service mode, restarting, and pressing CMD-OPT-p-r simultaneoulsy on the keyboard. If not seen, remove front bezel 922-2111 and check cables. See procedure for fixing the LCD display in Section IV. No LCD Display above. If seen in service mode but no boot THEN

  4. type "set-defaults" at Open Firmware, and type boot. Machine may reset, but the monitor should show attempted boot to cd, fd:diags or disk2:aix. Note that "set-defaults" will reset the boot path and passwords. If still no boot THEN

  5. Isolate the drive so that only the CD-ROM drive is in the drive trays. Type "probe-scsi1" at Open Firmware if the CD is in one of the top four tray positions. If the CD is in one of the bottom 3 tray positions, type "probe-scsi2". If Open Firmware sees the CD drive in the approriate position then put other drives back in and verify again. If fail then isolate to the other device which could have an incorrect, missing, or misplaced SCSI ID jumper. If the CD-ROM is never seen by Open Firmware THEN

  6. Replace with known good CD Drive. If success, isolate to either the CD drive or its cable set/Drive B>

    Transfer interrupted!