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Professional 325 Troubleshooting Guide

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Rear panel: the four red self-test LEDs and the green DC LED sit beside the video connector (DEC)

Fault-finding on the Professional 325, from DEC's Professional 300 Series Technical Manual (EK-PC350-TM-001) and the Professional 380 Pocket Service Guide (EK-PC380-PS-003), which also covers the 325 and 350.[1][2] DEC's service method works to the field replaceable unit and assumes one FRU has failed; if the symptoms change as parts are swapped, follow the current symptom.[3]

Power-up sequence

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When the power switch is turned on, all four red LEDs on the rear panel light as a lamp test. The power-up self-test then checks the system core (CPU, memory, self-test ROM and memory management), the base options on the system module (communications port, clock, floating point adapter if fitted, printer port, battery and battery-backed RAM, video/keyboard port) and finally each option module from its own ROM. If everything passes, the LEDs go out, the DIGITAL logo appears and the system boots.[4][5] A failure is shown on the screen as a picture of the system with the failing part highlighted, an error code and an ID number; the LEDs give the same information when the screen cannot.[4] A picture of a diskette with a question mark means no bootable volume was found; the ROM then keeps retrying the boot sequence.[6]

No response at power-up

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No response at power-up (EK-PC380-PS-003, Table 1-1)
Symptom Check Action
Nothing happens at the power switch Power cord, circuit breaker, wall outlet Reconnect the cord; reset the breaker by pushing it in; check the outlet and the cord with a meter
Fan runs but the green LED on the back is off Power cable from the supply to the system module Reseat it; otherwise replace the power supply
Green LED on, all four red LEDs off, screen blank Monitor cable and controls; memory daughterboards Reconnect the monitor cable, adjust the controls, reseat the daughterboards, then try another monitor
Green LED on, one or more red LEDs on Self-test failure Read the LED code below

[7] DEC asks for a restart with the power switch if the screen stays blank for more than two minutes.[7]

Rear-panel LED codes

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The Professional 325 and 350 system module reports its self-test result on four red LEDs, numbered 3 to 0 here as in DEC's table:[8]

Indicator (LED) error codes, Professional 350 system module (EK-PC350-TM-001, Table 5-6)
LED 3 LED 2 LED 1 LED 0 Meaning
off off off off No errors
off off off on Error in bus slot 0 (physical slot 1)
off off on off Error in bus slot 1 (physical slot 2)
off off on on Error in bus slot 2 (physical slot 3)
off on off off Error in bus slot 3 (physical slot 4)
off on off on Error in bus slot 4 (physical slot 5)
off on on off Error in bus slot 5 (physical slot 6)
on off off on Keyboard failed
on off on off No boot found
on off on on Monitor cable not present
on on off off Memory in slots 0 and 1 both failed
on on off on Memory in slot 1 failed (low bank)
on on on off Memory in slot 0 failed (low bank)
on on on on System module failed (all four stay lit after the lamp test)

[8] The remaining two combinations are reserved. The Professional 380 uses a different system module, and its pocket service guide's LED table is laid out for it; use the table above for a 325.[8][3]

Power supply faults

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H7862 behaviour (EK-PC350-TM-001, chapter 13)
Symptom Cause
Fan at half speed, green LED off, no output Voltage select switch at 240 V on 120 V mains
Internal fuse blown Switch at 120 V on 240 V mains; if the breaker also tripped within 3 to 8 seconds, the primary capacitors and possibly more parts are damaged
Supply shuts down and stays off Overvoltage latch: +5 V above 7.0 V, +12 V above 14.5 V or −12 V beyond −14.0 V; remove the power to reset it
Supply cycles off and restarts slowly Overcurrent shutdown (+5 V 21 to 29 A, +12 V 11 to 15 A) followed by soft start; look for a short on an output
Supply stops switching Start-up supply fallen to 8.75 V or below
System does not start although the outputs are present DCOK not asserted: +5 V below 4.7 ±0.2 V, +12 V below 11.1 ±0.3 V or −12 V below 10.8 ±0.3 V in magnitude

[9][10] Measure at the 16-pin connector J2: +5 V on pins 6 to 9, +12 V on pin 5, −12 V on pin 4, DCOK on pin 1, POK on pin 3, ground on pins 10 to 16.[11] At power-up DCOK follows the outputs by at least 3 ms and POK follows by at least 70 ms; at power-down POK drops first and DCOK at least 4 ms later, giving the CPU time to run its power-fail routine.[12] The H7862 has no adjustments.[13] Work inside it only after the input capacitors have discharged; see Professional 325 Capacitor Replacement Guide.

Clock and configuration

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The clock chip's "valid RAM and time" bit is cleared if its supply has fallen too low, and the date, time and the boot devices stored in battery-backed RAM may then be wrong.[14][6] A fully charged pack (48 hours of running) should hold the clock for at least ten days. The charger is a voltage divider from +12 V that supplies 10 mA.[14][15]

Maintenance ODT

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The F-11 microcode includes a console emulator (micro-ODT) reached through the printer port. Connect a terminal with DEC's terminal cable BCC08, which links pins 8 and 9 of the printer connector; the printer cable BCC05 does not, and without the link the console registers read as zero. ODT is entered by a HALT instruction in kernel mode, or by BREAK from the terminal when the break-enable bit in the system control register is set. It accepts 16-bit addresses and the usual PDP-11 ODT commands, including / to open a location, P to proceed and H to toggle a halt request for single-stepping.[16]

Diagnostics diskettes

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DEC's maintenance services diskettes run under P/OS: boot the P/OS diskette in drive 1, then at the prompt insert the installation/maintenance application diskettes in drives 1 and 2. The system unit test checks the diskette drive, printer and communications ports (internally looped back), the floating point processor and any option modules; service mode, entered with F12, F19 and F5, allows single or repeated passes and external loopback with connectors fitted. A keyboard test, printer test, configuration display and RX speed test are also included.[17]

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References

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  1. ↑ Digital Equipment Corporation, Professional 300 Series Technical Manual, EK-PC350-TM-001, December 1982 (File:Professional 300 Series Technical Manual (EK-PC350-TM-001, 1982).pdf).
  2. ↑ Digital Equipment Corporation, Professional 380 Pocket Service Guide, EK-PC380-PS-003, June 1986 (File:Professional 380 Pocket Service Guide (EK-PC380-PS-003).pdf).
  3. ↑ 3.0 3.1 DEC, EK-PC380-PS-003, pp. 1 to 2, sections 1.1.1 and 1.1.2.
  4. ↑ 4.0 4.1 DEC, EK-PC350-TM-001, p. 5-5, section 5.2.3.4, power-up self-tests.
  5. ↑ DEC, EK-PC350-TM-001, p. 3-1, section 3.2.2, indicators.
  6. ↑ 6.0 6.1 DEC, EK-PC350-TM-001, p. 5-6, section 5.2.3.5, boot sequence.
  7. ↑ 7.0 7.1 DEC, EK-PC380-PS-003, pp. 15 to 16, section 1.5 and Table 1-1, no response at power-up.
  8. ↑ 8.0 8.1 8.2 DEC, EK-PC350-TM-001, p. 5-33, Table 5-6 and Figure 5-15, indicator (LED) error codes.
  9. ↑ DEC, EK-PC350-TM-001, p. 13-4, Table 13-1, AC voltage switch settings, and warning.
  10. ↑ DEC, EK-PC350-TM-001, pp. 13-5 to 13-9, protection circuits, Table 13-2 and the DCOK thresholds.
  11. ↑ DEC, EK-PC350-TM-001, p. 13-10, Table 13-3.
  12. ↑ DEC, EK-PC350-TM-001, pp. 13-8 to 13-9, section 13.4.3 and Figure 13-9, power status timing.
  13. ↑ DEC, EK-PC380-PS-003, p. 80, section 2.8, power supply note.
  14. ↑ 14.0 14.1 DEC, EK-PC350-TM-001, p. 5-9, section 5.2.12, battery backed-up clock and RAM.
  15. ↑ DEC, EK-PC350-TM-001, p. 5-54, section 5.3.13.2, battery charger and voltage sensor.
  16. ↑ DEC, EK-PC350-TM-001, pp. 5-119 to 5-126, sections 5.4.14 and 5.4.15, maintenance ODT and maintenance terminal.
  17. ↑ DEC, EK-PC380-PS-003, pp. 4 to 15, section 1.4, maintenance services tests.
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