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Professional 380 Capacitor Replacement Guide

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Professional 380 system module (DEC Figure 6-2)
Professional 380 system module (DEC, EK-PC300-V1-001, Figure 6-2)

Capacitor values for the Professional 380 from DEC's PC380 drawing set, MP-01922 (June 1984).[1] The Professional 380 system board has no aluminium electrolytics. The electrolytics that age are in the H7862 power supply, which the 380 shares with the Professional 325 and Professional 350, and in the VR201 monitor.

Warning: the H7862's two input capacitors run at 250–350 V DC and DEC warns that they hold a high voltage for up to five minutes after switch-off.[2]

System board (5416237)

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The PC380 system board parts list, revision B, released October 1984, covers variations AC, AH, AJ and AP. Its only bulk capacitors are solid tantalums; the rest are ceramic.[3]

PC380 system board tantalum capacitors
Reference Value Rating Type DEC part
C23, C24, C25, C47, C48, C49 15 µF 20 V Solid tantalum 1004812-00
C5 10 µF 20 V Solid tantalum 1004813-00

[3]

The same list gives D8 as the LED assembly of one green and four red LEDs, the rear-panel self-test display.[3]

H7862 power supply

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DEC's recommended spare for the Professional 380 is the H7862-C.[4] The PC380 drawing set includes the H7862 print set, MP-01320 revision B, whose title block covers the H7862-00 and H7862-B. Its contents list circuit board 5415086 with a parts list and schematic, but for the board the scan holds only its assembly drawing, at revision H, and its schematic, at revision L.[5] ECO 5415086-ML010 on the assembly drawing adds a capacitor, C59. The revision L schematic gives the same values as the revision D parts list in the PC350 print set for the input capacitors C1 and C2 (1100 µF 200 V) and for C8, C13, C20, C21, C32 and C56.[6][7] The full revision D list, with schematic positions, is on Professional 325 Capacitor Replacement Guide; check the parts on your board against it.

To take the supply out, see Professional 380 General Maintenance.

Clock battery

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The KDJ11-C mother board assembly includes a three-cell 3.75 V nickel-cadmium battery pack, 1219245-00, mounted on the rear of the card cage.[8][9] After replacing it, DEC's instruction is to leave the computer on for at least 48 hours to charge it.[9]

VR201 monitor

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The VR201's capacitor list is on DECmate III Capacitor Replacement Guide.

After the recap

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Check the supply outputs with the system running. DEC's limits for the H7862 are ±5% on +5.1 V, +12.1 V and −12 V, and the supply asserts DCOK only when the outputs exceed 4.7 V, 11.1 V and 10.8 V (magnitude).[10][11] Confirm that the self-test ends with all four red LEDs off and the green LED lit; see Professional 380 Troubleshooting Guide.

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References

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  1. ↑ Digital Equipment Corporation, PC380 engineering drawings, MP-01922, June 1984 (File:Professional 380 PC380 Engineering Drawings (MP-01922, June 1984).pdf).
  2. ↑ Digital Equipment Corporation, Professional 300 Series Technical Manual, Volume 1: Kernel System, EK-PC300-V1-001, June 1985, pp. 10-4 to 10-6 (File:Professional 300 Series Technical Manual Volume 1 (EK-PC300-V1-001).pdf).
  3. ↑ 3.0 3.1 3.2 DEC, MP-01922, PC380 system board parts list 5416237-0-DBP, revision B, sheet A1 (PDF p. 19).
  4. ↑ DEC, EK-PC380-PS-003, p. 122, Table 2-2. H7862-C power supply.
  5. ↑ DEC, MP-01922, H7862 print set MP-01320 revision B, table of contents and unit variations (PDF p. 40).
  6. ↑ DEC, MP-01922, H7862 circuit board assembly E-UA-5415086-0-0 revision H with ECO 5415086-ML010 (PDF p. 50), and schematic D-CS-5415086-0-1 revision L, sheet 1 (PDF p. 51).
  7. ↑ Digital Equipment Corporation, PC350 field maintenance print set, MP-01394-00, H7862 circuit board parts list 5415086-0-DBP, revision D, sheets A1 to A4 (PDF pp. 55 to 58) (File:Professional 350 PC350 Field Maintenance Print Set (MP-01394-00).pdf).
  8. ↑ DEC, MP-01922, KDJ11-C large system unit mother board parts list (PDF p. 16). Battery 1219245-00.
  9. ↑ 9.0 9.1 Digital Equipment Corporation, Professional 380 Pocket Service Guide, EK-PC380-PS-003, June 1986, p. 90 (File:Professional 380 Pocket Service Guide (EK-PC380-PS-003).pdf).
  10. ↑ DEC, EK-PC300-V1-001, p. 10-11, section 10.6.2. Output regulation.
  11. ↑ DEC, EK-PC300-V1-001, p. 10-9. DCOK regulation thresholds.
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