PS/2 FAQ, App D

Micro Channel Adapter Errors
     I/O Channel check 
     DMA timeout 

   On DMA timeout errors, note the arbitration level displayed on the screen. Go to the "View configuration" screen and see which device has that same arbitration level. Suspect that device is defective. 

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. 

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, supported/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 available (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 power supply voltages. If the voltages are correct, replace system board. If voltages are incorrect, replace the power supply. 85/90/95/500 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 are only expecting 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. 

      Stolen from The Microchannel Enthusist's Page... 

Device Size Code     -----------------+ +--------- Unit Reference Code 
                                      | | 
Adapter MCA-Slot     ----------------+| |+-------- Sense Key Code 
                                     || || 
Logical Unit Number  ---------------+|| || +------ Additional Sense Code 
                                    ||| || | 
Physical Unit Number --------------+||| || | 
                                   |||| || | 
Device Code Number   ---------+--+ |||| || | 
                              |  | |||| ||++ 
                              |  | |||| |||| 
                              0210 401H 9231 
         Basically the SCSI Error Codes consist out of an 8-character output like a General Error Code, but have an additional 4-character Error Return Code at the end, which helps to specify the nature of the error.  There are small differences between SCSI-Device Errors and SCSI-Adapter Errors. These are explained when neccessary. 

SCSI Error Code Tables 

      Major Error Code -----------+---+
                                  |   |
                                  |   |
      Trailing Zeros   -------- 0024 01XX
      to fill 8 digits                 ||
                                       ||
      Minor (diagnostic Error Code)----++

      The Error Code is written in the 4 + 4 style as it appears on a PS/2 Mod. 95 LED-panel and in the Premium  Line "extended 8-digits" form. The bold part in the middle is the so called "Major Error Code" and -basically and in large parts- identical with the PC/AT Error Codes and those used on earlier PS/2 machines. 

      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

Codes I9990
         These have to do with the Initial Microcode Load on the 76/77, 85, 90, 95, and 500 systems.(and the TP700/720!) see I9990

Clearing 96 8N1 
From Peter Wendt- 
      Do the following: 
      - push a piece of card under the CMOS-buffer battery clip to have it isolated 
      - toggle the Password Override Jumper 
      - wait 20 minutes 
      - remove the card from under the battery clip 
      - start the system with a known good board & appropriate ref.disk 

      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)
.