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Professional 350 General Maintenance

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

Maintenance of the Professional 350 system unit. The 350 shares its enclosure, H7862 power supply, system module and RX50 drive with the Professional 325, so the shared checks (voltage selector, first power-up of a stored machine, cleaning, diskette handling and opening the system unit) are on Professional 325 General Maintenance.[1] The 350 adds the RD hard disk and its controller and more option slots; those, the memory, and repair experience with the clock battery and the RX50 follow.

The VR201 monitor contains a CRT; see CRT Discharge Procedure and Rainbow 100 General Maintenance for DEC's VR201 adjustment procedure.

Site

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Professional 300 series site requirements (DEC section 2.2)
Item Requirement
Clearance 15 cm (6 in) on all sides; ventilation ports kept clear
Lighting Away from direct sunlight
Power 115 or 230 V AC, 47–63 Hz, 320 W maximum
Temperature 10–40 °C (50–104 °F)
Relative humidity 20–80%, maximum wet bulb 25 °C, minimum dew point 2 °C

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Hard disk

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DEC's caution: a sudden shock, such as dropping the drive onto a hard surface, will destroy it.[3]

Controller

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The hard disk controller goes in slot 1 of the card cage, because of cable restrictions.[4] DEC made two versions. The RCD50 controller, 54-15134 (the 00 suffix is assumed), works only with the RD50 and RD51; the RCD52 controller, 54-15134-01, works only with the RD52. The part number is printed on the board.[5]

Removing the drive

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  1. Take off the top cover.
  2. Unplug the two I/O cables from the controller board by pulling straight up on their white pull tabs.
  3. Push down on the release tab below the front of the drive with a pen and slide the drive about 5 cm (2 in) forward.
  4. Unplug the 4-wire DC power cable from the back of the drive.
  5. Slide the drive out. DEC's instruction is to replace a drive with the same type.[6]

When fitting a drive, connect its signal and power cables, then slide it in until it clicks into place.[3]

RD drives for the Professional (DEC section 1.2)
Drive Formatted capacity Average access Track density
RD50 5 MB 170 ms 255 tracks per inch
RD51 10 MB 85 ms 345 tracks per inch
RD52 32 MB 37.5 ms 695 tracks per inch

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See Hard Drive Maintenance and Repair.

Option modules and memory

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Option modules plug into the CTI bus card cage on zero insertion force connectors. Remove the top cover and the screw holding the card cage door, open the door, hold the module by its connector and pull the handle out by turning it 90° clockwise, slide the module into its slot, then turn the handle straight up and push it in toward the module.[8] The extended bit map module goes in the slot next to the bit map video controller, joined to it by a flat cable.[4]

RAM daughter modules plug into the system module at J1 and J2.[9] DEC's 128 KB module, the MSC11-A (5415084), uses sixteen 64K × 1 dynamic RAMs; the print set lists Fujitsu, Hitachi and NEC versions.[10][11] A VCF member who owned a 350 from new upgraded his memory by replacing all the chips on the small daughter modules with 256K parts, and reported that it worked.[12]

Clock battery

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The battery is a three-cell nickel-cadmium pack, DEC 12-19245-00, on connector J3 of the system module and mounted at the back of the card cage.[13][9] Its removal and DEC's charging figures are on Professional 325 Capacitor Replacement Guide.

Community experience:

  • One owner removed the pack ten years before reviving his 350, but leakage had already damaged the board round the battery connector. Cleaning and repairing the tracks did not cure the clock fault; the clock chip and a nearby 74LS04 had both failed.[14]
  • Other owners report Professional 350 and 380 machines with batteries dead for decades still booting.[14]
  • Another owner replaced the 3.6 V pack with cells taken from a new cordless telephone battery.[12]

Remove or replace the pack on any machine that has been stored, and check the area round J3 for corrosion. See Battery Explosion, Capacitor or Corrosion Damage.

RX50 drive

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DEC treated the RX50 as a single field replaceable unit, to be adjusted only in a special test configuration.[15] Its service-mode RX speed test reports the spindle speed after five minutes' running; DEC's limit is ±1.00 and a drive outside it was to be replaced.[16]

Owners repair them. One RX50 in a Professional 350 had a seized spindle; once freed it ran at 293 r/min, measured by attaching it to a PC, and the self-test reported error 330, "drive speed not in limit", until the speed was raised to 301 r/min.[14] Another member's advice for a long-stored RX50 was cleaning, lubricating the head lead screw, and new or re-glued pads on the head pad arm.[14] See Floppy Drive Repair.

Routine checks

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  1. Make the checks on Professional 325 General Maintenance before the first power-up.
  2. Check the battery and the board round J3.
  3. Check that the hard disk controller is in slot 1 and is the right version for the drive.
  4. Switch on and watch the four red and one green LEDs on the back; see Professional 350 Troubleshooting Guide.
  5. Run the maintenance services system unit test, which takes about two and a half minutes in customer mode.[17]
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References

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  1. ↑ Digital Equipment Corporation, Professional 300 Series Technical Manual, Volume 1: Kernel System, EK-PC300-V1-001, June 1985, p. 1-2 (File:Professional 300 Series Technical Manual Volume 1 (EK-PC300-V1-001).pdf).
  2. ↑ DEC, EK-PC300-V1-001, p. 2-1, section 2.2. Site preparation.
  3. ↑ 3.0 3.1 DEC, EK-PC300-V1-001, p. 2-7, section 2.3.3.3. Hard disk installation and caution.
  4. ↑ 4.0 4.1 DEC, EK-PC300-V1-001, p. 2-6. Extended bit map module position; hard disk controller in slot 1.
  5. ↑ DEC, EK-PC380-PS-003, p. 65. RD hard disk controller versions.
  6. ↑ DEC, EK-PC380-PS-003, pp. 66 to 68. RD hard disk drive removal.
  7. ↑ DEC, EK-PC300-V1-001, pp. 1-5 to 1-7. RX50 and RD drive specifications.
  8. ↑ DEC, EK-PC300-V1-001, p. 2-5, section 2.3.3.2. Module installation.
  9. ↑ 9.0 9.1 DEC, EK-PC300-V1-001, p. 5-2, Figure 5-2. J1 and J2 memory, J3 battery and the battery pack.
  10. ↑ DEC, MP-01394-00, CT memory 128 KB parts list 5415084 (PDF p. 91).
  11. ↑ DEC, EK-PC300-V1-001, p. 11-1. RAM daughter modules of sixteen 64K × 1 chips, 128 KB each.
  12. ↑ 12.0 12.1 "Pro 350 speaker and date/time error", Vintage Computer Federation forum, February 2016, forum.vcfed.org. Replacement battery cells; memory upgrade with 256K chips.
  13. ↑ Digital Equipment Corporation, PC350 field maintenance print set, MP-01394-00, KDF11-C large system unit motherboard parts list (PDF p. 11) (File:Professional 350 PC350 Field Maintenance Print Set (MP-01394-00).pdf).
  14. ↑ 14.0 14.1 14.2 14.3 "Pro 350 revival", Vintage Computer Federation forum, thread started 18 July 2025, forum.vcfed.org. Battery damage, clock repair, RX50 spindle and speed, owners' reports of dead batteries.
  15. ↑ DEC, EK-PC380-PS-003, p. 64. The diskette drive is a single FRU.
  16. ↑ Digital Equipment Corporation, Professional 380 Pocket Service Guide, EK-PC380-PS-003, June 1986, p. 14, section 1.4.12, RX speed test (File:Professional 380 Pocket Service Guide (EK-PC380-PS-003).pdf).
  17. ↑ DEC, EK-PC380-PS-003, p. 6, section 1.4.3.1. System unit test.
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