DECpc 433 Troubleshooting Guide

Rear of a DECpc 433 Workstation (model PCW10-A2). The rotary video select switch beside the video connector is the first thing DEC checks when there is no picture (bitsavers.org)

Fault-finding on the DECpc 433 Workstation from chapter 2 of DEC's DECpc 433 Workstation Service Guide (ER-PCW10-SV-001) and the Technical Reference Manual (ER-PCW1A-TR). The BIOS is Phoenix's 80486 ROM BIOS PLUS.

DEC's first steps

1. Check the power indicators on the system box, the SCSI expansion box, the monitor and any peripherals.
2. Check for loose cables and connections.
3. Switch on. If the machine does not boot, switch off, wait 20 seconds and switch on again.
4. Note any POST message or beep code and act on it using the tables below.

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. 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.

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

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.

Beep codes

When POST cannot show a message it sounds a beep code and writes a value to I/O port 80h, which a POST card can read. A code such as 2-1-4 is a burst of two beeps, one beep, then four.

Fatal and non-fatal beep codes (DEC Tables 2-3 and 2-4)

Beeps	Port 80h	Error
1-1-3	02h	RTC write/read failure
1-1-4	03h	ROM BIOS checksum failure
1-2-1	04h	Programmable interval timer failure
1-2-2	05h	DMA initialisation failure
1-2-3	06h	DMA page register write/read failure
1-3-1	08h	DRAM refresh verification failure
1-3-3	0Ah	First 64 KB DRAM chip or data line failure
1-3-4	0Bh	First 64 KB DRAM odd/even logic failure
1-4-1	0Ch	First 64 KB DRAM address line failure
1-4-2	0Dh	First 64 KB DRAM parity test in progress or failure
2-1-1 to 2-4-4	10h to 1Fh	Bits 0 to F of the first 64 KB of DRAM, in order (2-1-1 is bit 0, 2-1-4 bit 3, 2-4-4 bit F)
3-1-1	20h	Slave DMA register failure
3-1-2	21h	Master DMA register failure
3-1-3	22h	Master interrupt mask register failure
3-1-4	23h	Slave interrupt mask register failure
3-2-4	27h	Keyboard and mouse controller test failure
3-3-4	2Bh	Screen memory test failure (non-fatal)
3-4-1	2Ch	Screen initialisation failure (non-fatal)
3-4-2	2Dh	Screen retrace test failure (non-fatal)

The intelligent graphics controller has its own codes of long and short beeps and writes nothing to port 80h:

Intelligent graphics controller beep codes (DEC Table 2-5)

Long	Short	Failed test
1	1	VGA RAMDAC
1	2	Monitor detection (RGB line loading or BT459 test circuit)
1	3	VGA display memory
1	4	VGA retrace (no vertical retrace)
1	5	Other adapter (a CGA or MDA card fitted and failing)
1	6	Xilinx programming
2	1	Frequency synthesiser (SC22318) programming
2	2	BT459 RAMDAC register test
2	3	GSP POST time-out
2	4	Register read/write to the i486 registers and GSP configuration register
2	5	Frame-grab hardware
2	6	GSP memory (VRAM and DRAM)
3	1	Controller disabled by a reserved video switch setting

System box faults

System box, disk and monitor faults (from DEC Tables 2-6 to 2-8)

Problem	Possible cause	Action
No response at switch-on	Not plugged in, or no power at the outlet	Plug in; try another outlet
Power on, no picture	Video select switch in the wrong position; monitor off; monitor cable wrong	Check the switch position; switch the monitor on; check the cable
Partly highlighted characters, rolling or flickering picture, wrong colours	Video select switch wrong; monitor adjustment; bent pins in the monitor cable	Check the switch; adjust; straighten pins and reseat
Colour monitor shows monochrome	System box switched on before the monitor	Switch the system box off, the monitor on, then the system box on
Hangs at start-up although its Ethernet address is set up on the server	Software not installed on the server, network failure, or network select switch in the wrong position	Check with the network administrator; set the network select switch correctly
Will not boot from the IDE disk	No operating system, unformatted or unpartitioned disk, wrong jumpers or drive type, loose cable	Install, format or partition; check jumpers; run Setup
Will not boot from the diskette	Drive ID not set to 1, no system files, worn diskette, loose cable	Set the drive ID to 1; use a bootable diskette
No response to the keyboard	Keyboard password set; keyboard unplugged or in the mouse port	Enter the password; plug into the keyboard port

SCSI expansion box

The expansion box takes its mains from the system box. If its power light is out, check that its cord is plugged into the system box and that the system box is plugged in; otherwise its 63 W supply has failed. If the machine will not boot from a SCSI disk, DEC's list is: no operating system, partition missing, drive jumpers, SCSI ID conflicts, terminating resistors left on the drive, the external terminator missing, or Setup not configured for SCSI.

Power supply

DEC treats the 105 W supply as a replaceable unit and publishes no component data for it. Its outputs should be +5 V ±5% (up to 18 A), +12 V ±5% (1 A, 2 A peak), −12 V ±10% and −5 V ±10% (0.2 A each). Warning: the supply is mains powered; unplug the system box before removing it.

Clearing passwords and CMOS

Jumpers on the system board clear a forgotten password or the CMOS RAM:

System board jumpers (DEC Table 4-13)

Feature	Normal (default)	Clear
Password	E1-1 and E1-2	E1-2 and E1-3
CMOS RAM	E1-4 and E1-5	E1-5 and E1-6

Related pages

• DECpc 433
• DECpc 433 General Maintenance
• DECpc 433 Documentation
• Battery Explosion, Capacitor or Corrosion Damage
• Hard Drive Maintenance and Repair