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Professional 325 General Maintenance

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Rear of the Professional 300 series system unit: voltage select switch, circuit breaker, power inlet, connectors and the self-test LEDs (DEC)

Routine care of the Professional 325, from DEC's Professional 300 Series Technical Manual and service guides. The 325 shares its system module, power supply, RX50 drive, monitor and keyboard with the Professional 350, so the same procedures apply to both.[1] Capacitors and the clock battery are covered in Professional 325 Capacitor Replacement Guide and faults in Professional 325 Troubleshooting Guide.

Before powering up a stored machine

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  1. Check the voltage select switch on the rear panel against your mains before the first power-up, and every time the machine moves. Set to 120 V on a 240 V supply, the H7862's internal fuse blows; if the circuit breaker then trips within 3 to 8 seconds, the primary capacitors and possibly more parts are destroyed. Set to 240 V on 120 V mains, the fan runs at half speed, the green DC LED stays off and the supply delivers nothing.[2][3]
  2. Inspect the clock battery pack and the system module around its connector J3 for leakage. The pack is a three-cell nickel-cadmium unit on a two-wire cable; see Professional 325 Capacitor Replacement Guide for removal and Battery Explosion, Capacitor or Corrosion Damage for cleaning.[4][5]
  3. Consider the H7862's electrolytic capacitors, and remember that its input capacitors hold high voltage for up to five minutes after switch-off.[2]
  4. Clean the inside of the system unit. The power supply fan draws air in through the vents on the right side of the supply and across the whole chassis, cooling the option modules and drive motors, so dust and blocked vents affect everything.[6]

Cleaning

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DEC's instructions: clean the covers of the system unit, monitor and keyboard with a cloth dampened in a mild solution of soap and water, and the monitor screen with a cloth dampened in a mild solution of isopropyl alcohol and water.[7]

Diskettes and the RX50 drive

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DEC's handling rules for the RX50's 5.25-inch diskettes:[7]

  • Keep diskettes in their envelopes, stored upright and loosely, away from magnetic fields (including the top of the system unit or monitor) and below 52 °C.
  • Label them with a felt-tip pen, not a pencil or ballpoint.
  • Never force the drive door closed, and never open a door or remove a diskette while either drive's indicator is lit.
  • Never touch the recording surface.

DEC's maintenance services diskettes include an RX speed test for the drive.[8] General drive cleaning and alignment are on Floppy Drive Repair.

Opening the system unit

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  • The system module is a circuit board on a metal plate that slides out of the bottom of the enclosure.[9] To reach the battery cable, slide it about 2 inches towards the rear.[5]
  • The power supply comes out after the top cover: unplug the 16-pin system module connector (pull its white tab straight back) and the 4-pin drive power connectors, pull the two release clips by the fan, and lift it out. Press down in the centre when refitting so that it latches.[10]
  • The fan is replaceable on its own (DEC part 12-13185-03) if it becomes noisy.[10]
  • The system identification number shown by the configuration display is held in a removable ID PROM on the system module; DEC's guide covers removing and refitting it as part of exchanging the module.[11][12]
  • If the system module is replaced or has been stored, leave the computer on for at least 48 hours to charge the clock battery fully, as DEC tells its engineers to advise customers.[12]

Checks

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Quick checks (EK-PC350-TM-001)
Check Expected
Rear LEDs at power-on All four red LEDs light as a lamp test, then go out when self-test passes; the DIGITAL logo appears on the screen
Green DC LED Lit whenever the power switch is on; off means no DC is reaching the system module
+5 V at J2 pins 6 to 9 5 V ±5 %
+12 V at J2 pin 5 12 V ±5 %
−12 V at J2 pin 4 −12 V ±5 %

[3][13][14] DEC's maintenance services diskettes run a system unit test (about two and a half minutes in customer mode), a keyboard test, a printer test, a configuration display and a bar pattern for setting the monitor controls; service mode, entered with F12, F19 and F5 in that order, adds the video alignment pattern and disk tests.[8]

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References

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  1. ↑ Digital Equipment Corporation, Professional 300 Series Technical Manual, Volume 1, EK-PC300-V1-001, June 1985, p. 1-2, section 1.1.4 (File:Professional 300 Series Technical Manual Volume 1 (EK-PC300-V1-001).pdf).
  2. ↑ 2.0 2.1 DEC, EK-PC350-TM-001, p. 13-4, section 13.3, warnings and Table 13-1, AC voltage switch settings.
  3. ↑ 3.0 3.1 DEC, EK-PC350-TM-001, p. 3-1, sections 3.2.1 and 3.2.2, controls and indicators.
  4. ↑ Digital Equipment Corporation, PC350 Field Maintenance Print Set, MP-01394-00, KDF11-C motherboard parts list, PDF p. 11, item 8 (File:Professional 350 PC350 Field Maintenance Print Set (MP-01394-00).pdf).
  5. ↑ 5.0 5.1 DEC, EK-PC380-PS-003, pp. 88 to 89, section 2.11, battery pack.
  6. ↑ DEC, EK-PC350-TM-001, p. 13-2, section 13.2.
  7. ↑ 7.0 7.1 DEC, EK-PC350-TM-001, p. 2-12, section 2.4, system upkeep.
  8. ↑ 8.0 8.1 Digital Equipment Corporation, Professional 380 Pocket Service Guide, EK-PC380-PS-003, June 1986, pp. 4 to 15, section 1.4, maintenance services tests (File:Professional 380 Pocket Service Guide (EK-PC380-PS-003).pdf).
  9. ↑ Digital Equipment Corporation, Professional 300 Series Technical Manual, EK-PC350-TM-001, December 1982, p. 1-2, section 1.1.1 (File:Professional 300 Series Technical Manual (EK-PC350-TM-001, 1982).pdf).
  10. ↑ 10.0 10.1 DEC, EK-PC380-PS-003, pp. 79 to 80, section 2.8, power supply.
  11. ↑ DEC, EK-PC380-PS-003, pp. 9 to 10, section 1.4.6, configuration display program.
  12. ↑ 12.0 12.1 DEC, EK-PC380-PS-003, p. 87, section 2.9, system module, notes.
  13. ↑ DEC, EK-PC350-TM-001, p. 5-33, Table 5-6 and Figure 5-15.
  14. ↑ DEC, EK-PC350-TM-001, pp. 13-10 to 13-11, Table 13-3 and section 13.6.
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