Professional 350 Troubleshooting Guide

Professional 300 series rear panel: the four red self-test LEDs are marked 4, 3, 2, 1, followed by the green DC LED (DEC, EK-PC300-V1-001, Figure 2-1)

Fault-finding on the Professional 350. The 350 uses the same system module, power supply and self-test as the Professional 325, so the shared material is on Professional 325 Troubleshooting Guide: no response at power-up, the rear LED codes, H7862 behaviour, maintenance ODT and the diagnostics diskettes. The on-screen error numbers, the hard disk and RX50 codes and repair reports from 350 owners follow.

Reading the self-test

At power-up all four red LEDs light as a lamp test; when the test passes they go out and the DIGITAL logo appears. If all four stay lit, the system module has failed. If the green DC LED is off with the power switch on, no DC is reaching the system module. The other LED patterns name a bus slot, the keyboard, a missing boot device, a missing monitor cable or a memory daughterboard; DEC's table is reproduced on Professional 325 Troubleshooting Guide. DEC's 1985 manual prints the code for memory slot 1 twice, once as "low bank" (Table 5-6) and once as "high bank" (Table 5-13).

When the monitor works, the self-test also shows a two-line error number on the screen: the slot number and an error code on the first line, and the identification number of the failing device on the second.

Selected system error numbers (DEC Table A-1)

Device ID	Device	Error	Meaning
1	Keyboard	60	Keyboard not functioning properly
1	Keyboard	75	Stuck key
14	Keyboard interface	1, 200–203	Unexpected interrupt, loopback time-out, overrun or framing error, data compare error
17	Printer interface	1, 200–203	As for the keyboard interface
23	Clock	21	Clock did not interrupt in proper time
24	Battery-backed RAM	22	Data compare error
25	Interrupt controller	1	No interrupts generated
401	RD50 controller	2	Internal power-up self-test error
401	RD50 controller	5, 21	Drive not ready, seek incomplete or write fault
401	RD50 controller	25–32	Data mark not found, track 0 error, ID not found, CRC errors
2004	RX50 controller	10, 20	Bad track 00 sensor, drive 0 or drive 1
2004	RX50 controller	30	Both drives failed to respond
2004	RX50 controller	120, 130	Selected diskette not ready; diskette not installed correctly
2004	RX50 controller	320	No index pulse
2004	RX50 controller	330	Drive speed not in limit
2004	RX50 controller	340	Bad format or blank disk
1002	Professional 350 video	2–7	Register, plane 1 memory, vertical retrace, counter, control or scroll register failure
1002	Extended bit map option	103–107, 203–207	Plane 2 or plane 3 memory, control or scroll register failure
Any	Slot option	376	Option has a bad ROM

Clock and battery: errors 000020 and 000023

Two owners have reported a 350 stopping with 000020 over 000023, which one of them read as error 20 from the clock (device 23), a code DEC's table does not list. On the machine in the 2025 report, the nickel-cadmium battery had leaked onto the board round its connector. Cleaning and repairing the tracks was not enough: the clock chip and a nearby 74LS04 had failed. The owner's conclusion was that this code points to the clock and a leaking battery, and that the 74LS04 and possibly the 32,768 Hz clock oscillator need replacing. Owners also report machines whose batteries have long been dead booting normally, so a flat battery alone does not stop a 350.

RX50 and booting

• Error 330 (drive speed not in limit) on a long-stored machine came from a stiff, slow spindle. Freed and set from 293 to 301 r/min, the drive passed. DEC's RX speed test in service mode measures the speed after five minutes' running and fails a drive outside ±1.00.
• The same machine gave 0130 (diskette not installed correctly) when started with no diskette in the drive, and booted from its hard disk once the RX50 controller was removed. Other owners' 350 and 380 machines start with an empty drive; the behaviour may depend on the RX50 controller's firmware.
• A Gotek floppy emulator works in place of an RX50, but one user found it needs a blank or non-system image in the first drive for the floppy subsystem to pass at boot.
• The RD50 and RD51 need the RCD50 controller (54-15134) and the RD52 the RCD52 (54-15134-01); the wrong controller will not work with the drive.

See Professional 350 General Maintenance for RX50 and hard disk handling.

Power supply

DEC treated the H7862 as a single replaceable unit; it is not adjustable. An overvoltage on any output latches the supply off, and DEC's 1985 manual says to remove power for at least five minutes before it will restart. The supply's capacitors, test points and warnings are on Professional 325 Capacitor Replacement Guide.

Monitor

On one Professional 350, a VR201 worked for a few boots, then lost vertical hold, showed the screen three times over and went black. VCF members recommended checking its capacitors first, and one had needed to recap his own VR201. The VR201 capacitor list is on DECmate III Capacitor Replacement Guide.

Related pages

• Professional 350
• Professional 350 General Maintenance
• Professional 350 Capacitor Replacement Guide
• Professional 325 Troubleshooting Guide
• Professional 380 Troubleshooting Guide