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PDP-11/70 General Maintenance

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H7420 supply with H744 regulators from the processor cabinet (DEC)

Routine care of the PDP-11/70, from DEC's PDP-11/70 Maintenance and Installation Manual (EK-11070-MM-002) and the annual preventive maintenance checklist in DEC Canada's 1170 Maintenance Service Guide (KA-K1170-MG-003).[1][2] Regulator settings and power faults are covered in PDP-11/70 Power Supply Service.

DEC's schedule

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DEC's field service PM for the 11/70 power system has two levels. Monthly: inspect the logic and power supply fans, clean the air filters and replace burnt-out indicators. Quarterly: inspect wiring and etch, vacuum the air vents and fan housings, and check the regulator voltages.[1]

Preventive maintenance times (EK-11070-MM-002, appendix E, excerpt)
Device Monthly Quarterly Semi-annually Annually
KB11-B, -C processor 15 min 2.5 h – 3 h
FP11-B – 1.5 h – –
RH70 – 30 min – –
KW11-L – 20 min 25 min 30 min

[3]

Visual inspection

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With all power off:[4]

  1. Check that no fan is obstructed, and clean the air filters inside the cabinet doors.
  2. Inspect the modules and backplane for broken wires and connectors.
  3. Inspect all wiring and cables for cuts, fraying, deterioration, kinks and strain, and repair them.
  4. Check regulators, fans and capacitors for mechanical security.
  5. Inspect the power supply capacitors for leaks, bulges or discoloration and replace any that show them.

Use a digital voltmeter for regulator voltages, an oscilloscope for ripple, and a VOM for continuity and resistance checks.[4]

Annual checklist

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DEC Canada's annual PM for the CPU and memory subsystem:[2]

  1. Check the eight CPU H744 regulators at F02A2, F09A2, F15A2, F44A2, F22A2, F18A2, F28A2 and F35A2 (+5 V ±0.1 V, 200 mV p-p), and the upper H7420's +8 V at B01B1 and +15 V at E13A1 and the lower H7420's −15 V at E13B2.
  2. Check the MK11 regulators at J18 and J21 (+5 VBB 4.9 to 5.3 V, +12 VBB 11 to 13 V, −12 VBB −10.5 to −13.5 V) and the H7441 at J21-7.
  3. Check the MJ11 regulators at the M8149 test points (+5 V ±0.25 V, +20 V ±1.0 V, −5 V ±0.25 V).
  4. Check all fans.
  5. Check the MK11 battery backup units for proper operation.
  6. Run the timing margin check: jumper F13J1 to E21T1, set R162 on the M8139 to 250 ns at D13T2 and run the instruction exerciser EQKC for one pass, set 140 ns and run it again, return to 150 ns and remove the jumper.
  7. Run EMKA for two passes.
  8. Power the MK11 off and on and return the system to the user.

DEC's manual allows ±250 mV on the processor +5 V regulators; the service guide's table uses ±0.1 V.[5][6]

Memory

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DEC's 11/70 memory tuning for the MJ11 starts with setting +5 V, −5 V and +20 V within 5 % and the bias voltage to 340 mV nominal, before adjusting strobe timing with the jumpers on the G235/G236 drivers (all in for the earliest strobe, all out for the latest, 3 ns steps over 300 to 350 ns).[7] The MK11 box controller sets each box's starting address and interleaving, and its battery status indicators show the state of the three battery backup units.[8][9]

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References

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  1. ↑ 1.0 1.1 Digital Equipment Corporation, PDP-11/70 Maintenance and Installation Manual, EK-11070-MM-002, May 1979, p. 4-100, section 4.5.3.1, H7420 preventive maintenance (File:PDP-11-70 Maintenance and Installation Manual (EK-11070-MM-002).pdf).
  2. ↑ 2.0 2.1 Digital Equipment of Canada, 1170 Maintenance Service Guide, KA-K1170-MG-003, April 1988, pp. 126 to 130, annual PM (File:PDP-11-70 Maintenance Service Guide (KA-K1170-MG-003).pdf).
  3. ↑ DEC, EK-11070-MM-002, p. E-1, appendix E, preventive maintenance schedule.
  4. ↑ 4.0 4.1 DEC, EK-11070-MM-002, pp. 4-77 and 4-103, visual inspection.
  5. ↑ DEC, EK-11070-MM-002, p. 4-104, H744 adjustment.
  6. ↑ DEC Canada, KA-K1170-MG-003, pp. 26 to 27.
  7. ↑ DEC Canada, KA-K1170-MG-003, pp. 141 to 143, MJ11 tuning.
  8. ↑ DEC Canada, KA-K1170-MG-003, p. 32, MK11 switches, jumpers and configuration rules.
  9. ↑ DEC, EK-11070-MM-002, p. 4-62, section 4.4.7, MK11 power supply cables and battery status indicators.
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