Editing DECpc 433 Troubleshooting Guide (section)

== Power-on self-test ==
POST tests the system board first: interrupt controller, 82340 chip set, CPU, keyboard controller, CMOS RAM, ROM checksum, timer, DMA, the first 64 KB of RAM and the cache controller. A failure there is fatal and is reported by beeps, an on-screen message, or fault LEDs on the system board and graphics controller. POST then checks the configuration in CMOS against the hardware, the rest of the memory, keyboard, serial and parallel ports, floppy and hard disk controllers and the graphics controller.<ref name="sg3" /> While it runs, the screen counts down from 240 to 000; the memory count can take up to 60 seconds. A clean run gives one beep; an error gives two beeps and a message.<ref name="sg5" />

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+ '''POST error messages (DEC Table 2-2)'''
! Count !! Code !! Message !! DEC's action
|-
| 240 || 0007 || No timer tick || Replace the system board
|-
| 200 || 0001 || Gate A20 failure || Replace the system board
|-
| 190 || 0009 || Timer 2 failure || Replace the system board
|-
| 180 || 0010 || Keyboard stuck key, keyboard controller, clock line, data line or keyboard failure || Check the keyboard connection and for a stuck key; replace the keyboard
|-
| 170 || 0041 || Pointing device failure || Check the mouse connection; replace the mouse
|-
| 160 || – || 640 KB base memory, 0 KB extended memory || Replace the system board
|-
| 150 || 0017 || Time-of-day clock stopped || Replace the system board
|-
| 100 || 0018 || Invalid configuration information || Run Setup
|-
| 090 || 0011 || Floppy disk drive failure || Check connections; replace the drive
|-
| 080 || 0015, 0016 || Hard disk controller failure; hard disk 0 failure || Check connections; replace the hard disk
|-
| 070 || 43 || No SCSI BIOS found || Check SCSI connections; replace the system board
|-
| 070 || 210–215 || SCSI target 0 not connected, faulty, not a disk, not ready, capacity read failed, or not 512-byte blocks || Check the expansion box connection and SCSI IDs, run Setup, or replace the drive
|-
| 070 || 200 || Host adapter diagnostic failure || SCSI hardware failure
|-
| 060 || 0021 || Optional ROM bad checksum || Correct the address conflict or replace the ROM
|-
| 060 || 71–8C || LAN memory, hardware, I/O, interrupt or mouse-interrupt failure || Replace the system board
|-
| 050 || 0019 || Time-of-day not set || Run Setup and set the time and date
|-
| 040 || 0020 || Keyboard is locked || Unlock the keyboard
|}
<ref name="sg7" />

Messages 0017, 0018 and 0019 all involve the battery-backed clock and CMOS RAM. Before replacing a system board for them, check the clock battery on header J8: DEC's parts list gives it as a 4.5 V pack, and on the machine photographed for bitsavers it is a non-rechargeable alkaline Duracell pack, now decades old. DEC's battery procedure ends with re-entering the configuration in Setup.<ref name="sg23" /><ref name="sg3p" /><ref name="photo" />