DECpc LP Troubleshooting Guide
Fault-finding on the DECpc LP range from chapter 4 of DEC's DECpc LP PC Service Maintenance Manual (K-MN-SD00000-21-JG00.A), with notes from David Hall's machines.[1][2]
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First steps
editDEC's initial troubleshooting:[1]
- Press Ctrl+Alt+Del. If the computer still does not start, switch off, wait until the hard disks have stopped, and switch on again.
- Check that every cable and connection is secure.
- Act on any POST message or beep code using the tables below, then restart.
- Run the diagnostic software (DEC used QAPlus/FE) and the BIOS Setup utility.
If the front button does nothing at all, check the linkage between the button and the switch inside the power supply before anything else; its rubber coupling tube perishes on these machines.[2] See DECpc LP Power Supply Service.
Beep codes
editWhen POST cannot show a message it beeps and writes a value to I/O port 80h. A code of 2-1-4 is a burst of two beeps, one beep, then four.[3]
| Beeps | Error |
|---|---|
| 1-1-3 | CMOS write/read failure |
| 1-1-4 | ROM checksum failure |
| 1-2-1 | Interval timer failure |
| 1-2-2 | DMA failure |
| 1-2-3 | DMA page register write/read failure |
| 1-3-1 | RAM refresh failure |
| 1-3-3 | First 64 KB RAM chip or data line failure |
| 1-3-4 | First 64 KB RAM odd/even logic failure |
| 1-4-1 | First 64 KB RAM address line failure |
| 1-4-2 | First 64 KB RAM parity failure |
| 2-1-1 to 2-4-4 | Bits 0 to F of the first 64 KB of RAM, in order (2-1-4 is bit 3) |
| 3-1-1 | Slave DMA register failure |
| 3-1-2 | Master DMA register failure |
| 3-1-3 | Master interrupt mask register failure |
| 3-1-4 | Slave interrupt mask register failure |
| 3-2-4 | Keyboard/mouse controller failure |
| 4-2-1 | Timer tick interrupt failure |
| 4-2-2 | Shutdown failure |
| 4-2-3 | Gate A20 failure |
| 4-2-4 | Unexpected interrupt in protected mode |
| 4-3-1 | RAM failure above 0FFFFh |
| 4-3-3 | Interval timer 2 failure |
| 4-3-4 | Time-of-day clock failure |
| 4-4-1 | Serial port failure |
| 4-4-2 | Parallel port failure |
| 4-4-3 | Maths coprocessor failure |
| 3-3-4, 3-4-1, 3-4-2 | Screen memory, initialisation or retrace failure (non-fatal) |
POST messages
edit| Message | DEC's action |
|---|---|
| No timer tick; Shutdown failure; Timer 2 failure | Replace the main logic board |
| Keyboard stuck key, controller, clock line, data line or failure | Check the keyboard connection; replace the keyboard |
| Mouse failure | Check the mouse connection; replace the mouse |
| Time-of-day clock stopped | Replace the RTC |
| Invalid configuration information | Run BIOS Setup |
| Diskette drive failure; hard disk controller failure; hard disk 0 failure | Run BIOS Setup, check connections, then replace the drive or controller |
| Optional ROM bad checksum | Correct the address conflict, or replace the ROM |
| Time-of-day not set | Run BIOS Setup and set the time and date |
| Keyboard is locked | Unlock the keyboard |
The clock and CMOS run from the original alkaline battery pack, if it is still fitted. Check and replace the battery before replacing the clock chip for "Time-of-day clock stopped" or "Invalid configuration information".[2][5]
Computer faults
edit| Problem | Possible cause | Action |
|---|---|---|
| No response at switch-on | Main logic board failure, or board jumpers set wrongly | Check the jumpers; replace the board |
| Power on, no picture | Brightness and contrast, monitor cable, VGA disabled by jumper or Setup | Adjust the monitor; check the cable; set J2 and Setup for on-board VGA |
| Colour monitor shows monochrome | Computer switched on before the monitor, or J11 set for mono | Switch the monitor on first; fit J11 for a colour monitor |
| Will not boot from the IDE disk | No operating system or partition, wrong drive type in Setup, drive jumpers, loose cables | Install or partition; set the drive type from the drive's label; check jumpers and cables |
| Will not boot from a SCSI disk | IDE still enabled, SCSI IDs or termination | In Setup set both hard disks to "Not Installed" and disable the IDE interface; with both fitted the computer boots from IDE |
| Will not boot from a diskette | Drive not enabled, "Boot From Diskette A" disabled, no system files, drive ID | Enable the drive and diskette boot in Setup |
| Disk cannot read or write | Drive type, controller disabled in Setup, diskette write protection enabled in Setup | Correct the Setup options |
| No response to keyboard or mouse | Password set; plugged into the wrong port; no mouse driver | Enter the password; swap the connectors with the power off; install the driver |
Memory and disk compatibility
editUse only 4 MB or 16 MB 36-bit SIMMs of 70 ns or faster in DEC's permitted combinations; see DECpc LP General Maintenance.[7] Hall finds the machines fussy about memory and likely to work only with fast-page-mode SIMMs.[2] A large modern disk or a CompactFlash card may not work with the BIOS, which has no LBA support; Hall suggests an XT-IDE ROM.[2]
A dead board
editHall's 433dxLP has never worked: no video, POST card codes 0A09 with no memory fitted and 2725 with memory, and a few beeps of an unusually low tone.[2]
Related pages
editReferences
edit- ↑ 1.0 1.1 Digital Equipment Corporation, DECpc LP PC Service Maintenance Manual, K-MN-SD00000-21-JG00.A, March 1996, p. 43 (File:DECpc LP Service Maintenance Manual (K-MN-SD00000-21-JG00.A).pdf). Initial troubleshooting.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 David Hall, "Digital DECpc 340dx LP/425sx LP/433dx LP/450d2 LP/466d2 LP", zxnet, last modified 2 February 2024, zx.net.nz.
- ↑ 3.0 3.1 DEC, K-MN-SD00000-21-JG00.A, pp. 44–45. Beep codes for fatal and non-fatal errors.
- ↑ DEC, K-MN-SD00000-21-JG00.A, pp. 45–46. POST and boot messages.
- ↑ DEC, K-MN-SD00000-21-JG00.A, p. 40. Replacing the computer battery.
- ↑ DEC, K-MN-SD00000-21-JG00.A, pp. 47–50. Computer, disk drive and monitor troubleshooting tables.
- ↑ DEC, K-MN-SD00000-21-JG00.A, p. 32. Memory configurations.