POST Errors
   Refer to the General and SCSI Error Codes below. If multiple errors occur during POST, resolve them in the order that they are presented. 
   Always cold boot and run Advanced Diagnostics (go into System Programs and at the main menu do a Ctrl-A) before replacing components when trying to resolve software problems. If diags don't fail, replacing components will probably not solve the problem. Refer to the software vendor for possible patches. The software may not be supported on the system. 

Multiple POST Error Proceedure
   If more than one error code is displayed, diagnose the first error code first. The cause of the first error code could cause other devices to fail. This is especially important with configuration errors.

   If no error codes appear, see if the error symptoms are listed in the Error list.

   If an adapter consists of multiple FRUs (memory for example) remove the optional FRUs one at a time to see if symptoms change before replacing the adapter.

   External surge suppressors may be the source for hard to diagnose problems.

PS/2 Beep Codes
A o (small o) indicates a short beep
A - (underscore) means a long beep

o            Normal Operation
o o           A problem exists, check config. Run diags, if no error code displayed
_ o           Display or display adapter problem.
_ o o         Display or display adapter problem.
_ o o o       Display or display adapter problem.
o o o o o o   Continuos short beeps. Check keyboard.
________      Continuos solid beep. System board.
 

Dead System (no POST, screen blank, no beep) 
   The most likely cause is a device that is shorting out the power supply. An improperly inserted memory module, a defective adapter or device can cause a short circuit. To prevent damage to a power supply, the system board must present a "POWER GOOD" signal to the power supply in 150mS or less. If this does not occur, then the power supply shuts down internally. 
   Known dufus tricks- SIMM inserted backwards (with enough force ANYTHING is possible). adapter not fully seated in expansion slot, power cord not plugged in, unsupported/defective adapter (Non-IBM adapter, like ALR..), or with a heavily loaded system, too many drives starting at once (overcurrent as the drives attempt to spin up- leave motor start jumper open to start drives after the controller interrogates them) 

Troubleshooting a Dead System
1.   Verify power is on (IS cord plugged in?). If the system has power, then go to #2 
2.    Remove all adapters, options, extra memory, etc. 
       Remove all external connections, KB, mouse, display, etc. 
3.    Plug in, power on and listen for a beep. The beep indicates POST has run. 
       Multiple beeps may occur. 
4A. If no beep is heard, verify continuity through speaker. If OK, replace system 
       board memory and retry # 3. 
          If still no beep, verify psu voltages. If voltages are OK, replace system board. 
        If voltages are incorrect, replace the power supply. 85/95 PS 90 PS 500 PS
4B.  If a beep occurs, reinstall adapters one at a time and return to step 3. When 
       something is added and the beep is no longer heard, the last item plugged in is 
       probably defective. At this point, it is not necessary to reconfigure the system 
       each time an adapter or device is added because we expect any beep. 

Batteries
   Defective or weak batteries can cause loss of all setup information. If only part of the setup is lost, the battery is probably NOT the cause. Innacurate time is usually caused by software. 

General SCSI Error Codes

SCSI Error Code Tables

Major Error Code -----------+---+

                            |   |

                            |   |

Trailing Zeros   -------- 0024 01XX

to fill 8 digits                 ||

                                 ||

Minor (diagnostic Error Code)----++

The 2 digits of the "Minor Error Code" is dependent on the type of the error and -mostly- only specified when running the Advanced Diagnostics. The minor error code is however often given at POST-Errors (after restarting the computer) and might specify a particular error condition. In case the minor error code is marked with "XX" in the follow-up error lists it means "Don't care" and it can be any character. 

Codes 100 - 159	Codes 160 - 199	Codes 200 - 299
Codes 300 - 999	Codes 1000 - 1499	Codes 1500 - 2999
Codes 3000 - 9999	Codes 10000 - 11999	Codes 12000-14999
Codes 15000-19999	Codes 20000-29999
For a chart how to determine a failing memory module on  Mod. 56/57, 76/77, 85 and 90/95 see Here !

That worked any time I'd landed on the "ASCII-console mode" during fiddling with SOD- / bad-DMA platforms and Kingston Turbochips :-) Moving only the jumper or only isolating the battery often did *not* cure it. Which is slightly strange. 
 (Ed. I just pull the battery and wait 5 minutes, then it autoconfigures with a 161/163, Date Time not set)