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Professional 350 Capacitor Replacement Guide

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Professional 350 system module and card cage (DEC Figure 5-2)
Professional 350 system module and card cage (DEC, EK-PC300-V1-001, Figure 5-2)

Capacitor values for the Professional 350 from DEC's PC350 field maintenance print set, MP-01394-00.[1] Almost all of the 350's aluminium electrolytics are in the H7862 power supply, which the 350 shares with the Professional 325 and Professional 380; the full H7862 list, its warnings and the post-recap checks are on Professional 325 Capacitor Replacement Guide. The boards particular to the 350 are listed here.

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 module (CT100, 5415101)

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The CT100 system module parts list, revision C, has no aluminium electrolytics. Its only bulk capacitors are solid tantalums:[3]

CT100 system module tantalum capacitors
Reference Value Rating Type DEC part
C23, C24, C25 15 µF 20 V Solid tantalum 1004812-00
C90 10 µF 20 V Solid tantalum 1004813-00

[3]

Video and memory boards

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Electrolytics on the video generator and memory board
Board Reference Value Rating Type DEC part
CT100 video generator (bit map video controller), 5415138 rev. D C2 8 µF 25 V Aluminium electrolytic 1012084-01
MSC11-A 128 KB memory, 5415084 C19 10 µF 35 V Aluminium electrolytic 1017472-00

[4][5]

The other capacitors on both boards are ceramic.[4][5]

H7862 power supply

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The supply's circuit board, 5415086 revision D, carries twelve aluminium electrolytics.[6] They are tabulated, with values, DEC part numbers, schematic positions and the notes on later board revisions, on Professional 325 Capacitor Replacement Guide, together with the replacement procedure and the output checks.

Clock battery

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The clock and configuration RAM run from a three-cell 3.75 V nickel-cadmium pack (12-19245-00) on J3.[7] One owner found that it had leaked onto the system module during storage.[8] See Professional 350 General Maintenance.

VR201 monitor

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The VR201's capacitor list, from DEC's print set MP-01410, is on DECmate III Capacitor Replacement Guide.

After the recap

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Check the outputs at the system module power connector J4 with the system running: +5 V on pins 6 to 9, +12 V on pin 5 and −12 V on pin 4, with DCOK on pin 1 and POK on pin 3.[9] DEC's limits are ±5% on all three outputs.[10]

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References

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  1. ↑ Digital Equipment Corporation, PC350 field maintenance print set, MP-01394-00, 1982 (File:Professional 350 PC350 Field Maintenance Print Set (MP-01394-00).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). Input capacitor voltage and warnings.
  3. ↑ 3.0 3.1 DEC, MP-01394-00, CT100 system module parts list 5415101-0-DBP, revision C, sheet A1 (PDF p. 15).
  4. ↑ 4.0 4.1 DEC, MP-01394-00, CT100 video generator parts list 5415138-0-DBP, revision D, sheet A1 (PDF p. 40).
  5. ↑ 5.0 5.1 DEC, MP-01394-00, CT memory 128 KB parts list 5415084 (PDF p. 91).
  6. ↑ DEC, MP-01394-00, H7862 power supply circuit board parts list 5415086-0-DBP, revision D, sheets A1 to A4 (PDF pp. 55 to 58).
  7. ↑ DEC, MP-01394-00, KDF11-C large system unit motherboard parts list (PDF p. 11). Battery 12-19245-00.
  8. ↑ "Pro 350 revival", Vintage Computer Federation forum, July 2025, forum.vcfed.org.
  9. ↑ DEC, EK-PC300-V1-001, p. 5-130, Table 5-24, J4 DC power.
  10. ↑ DEC, EK-PC300-V1-001, p. 10-11, section 10.6.2. Output regulation.
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