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MicroVAX 3100

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MicroVAX 3100
DEC's drawing of the Model 10 and Model 20 enclosures (owner's manual Figure 1-1)
Specifications
ManufacturerDigital Equipment Corporation
TypeDesktop VAX server and multi-user system
CPUModel 10 and 20: KA41-A CVAX, 90 ns, 1 KB first-level cache; later models KA41-D to KA59[1][2]
MemoryModel 10 and 20: 4 MB, up to 32 MB; Model 85 and 95: 16 MB, up to 128 MB[1][3]
StorageSCSI disks (RZ23 104 MB in the Model 10 and 20), TZ30 tape, RX23 diskette[4]
Display—
Sound—
PowerAuto-ranging 100–120 / 220–240 V; typically 160 W (Model 10 and 20), 215 W maximum (Model 85 and 95)[1][3]
DimensionsModel 10: 10.03 × 46.38 × 40.00 cm; Model 20: 14.99 × 46.38 × 40.00 cm[1]
WeightModel 10: 11.4 kg; Model 20: 17.8 kg, depending on configuration[1]
OS / FirmwareVMS, ULTRIX-32[4]
PredecessorMicroVAX II[2]

The MicroVAX 3100 is a series of desktop VAX systems from Digital Equipment Corporation, sold as the MicroVAX 3100 for multi-user work and as the VAXserver 3100 for dedicated server use.[4] All are SCSI-based machines in two desktop enclosures, the smaller BA42-A and the larger BA42-B, and they share their power supplies with the VAXstation 3100 and DECstation 2100 and 3100.[5] The first models, the Model 10 and Model 20, use the KA41-A CVAX processor; DEC's owner's manual for them is dated 1989. Later models running up to the NVAX-based Model 98 kept the same enclosures, the last being ordered until 2000.[4][2][5]

Restoring one usually means the power supply first: the H7821 and H7822 supplies have electrolytic capacitors that leak, and some carry RIFA mains filter capacitors.[6][7] See MicroVAX 3100 Power Supply Service, MicroVAX 3100 Maintenance Guide and MicroVAX 3100 Troubleshooting Guide.

Models

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MicroVAX 3100 models
Model CPU Enclosure and supply (Dehling)
10, 10e KA41-A CVAX 11.11 MHz; KA41-D CVAX+ 16.67 MHz (10e) BA42-A, H7821-00
20, 20e As 10 and 10e, larger enclosure BA42-B, H7822-00
30 KA45, 25 MHz BA42-A, H7821-00
40 KA45, 25 MHz BA42-B, H7822-00
80 KA47, 50 MHz BA42-B, H7822-00
85 KA55 NVAX, 62.5 MHz BA42-B, H7822-00
88 KA58 NVAX, 62.5 MHz BA42-B, H7822-00
90 KA50 NVAX, 72 MHz BA42-B, H7822-00
95 KA51 NVAX, 83.34 MHz BA42-B, H7822-00
96, 98 KA56, KA59 NVAX, 100 MHz BA42-B, H7822-00

[2][5][3] The CPU details are from Wikipedia; DEC's own documents confirm the KA41-A for the Model 10 and 20 and the KA55 and KA51 for the Model 85 and 95, and give the BA42B enclosure for the 85 and 95.[1][3] Restorers have found other supplies than Dehling's list suggests: Antonio Carlini found an H7822-00 in a Model 10, and Rob Jarratt's Model 95 has a supply made by a different manufacturer from the usual DEC units.[7][8] Read the label on the supply before ordering parts.

Hardware

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The Model 10 and 20 have a KA41-A CPU with a 90 ns cycle and 1 KB first-level cache, 4 MB of memory expandable to 32 MB, and 256 KB of ROM. They have one SCSI port, ThinWire and standard Ethernet (one at a time), three DEC423 MMJ asynchronous ports and one RS-232 modem port; the DSH32-B option adds eight asynchronous lines and one synchronous line.[1][4] The Model 10 takes up to three RZ23 disks and one RX23 diskette drive, the Model 20 up to five RZ23s and one or two RX23s.[4]

System defaults such as the boot device are kept in battery-backed memory. DEC says the batteries charge fully after 17 hours of running and then hold the settings for about four days.[9] Eight diagnostic LEDs on the rear panel light during power-up.[10]

The Model 85 and 95 use NVAX processors (KA55 and KA51), 16 to 128 MB on MS44 SIMMs, and a choice of SCSI disks, tape, diskette and CD-ROM drives in the BA42B enclosure; they draw up to 3.0 A at 110 V and 215 W.[3]

Known problems

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  • Leaking power supply capacitors. Peter Coghlan's MicroVAX 3100 would not start after storage: the diagnostic LEDs flashed briefly and the fans twitched. Five 1800 µF 25 V capacitors in its H7821 had leaked.[6]
  • RIFA filter capacitors in the supply.[7]
  • Model 95 supply. Rob Jarratt found memory modules dropping out and the 5.1 V output reading 5.3 V; he replaced the supply's electrolytics and a failed UC3842 PWM controller.[8]

See MicroVAX 3100 Troubleshooting Guide.

Documentation

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See MicroVAX 3100 Documentation.

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  • Rear panel of a Model 20 (DEC owner's manual Figure 2-2)
    Rear panel of a Model 20 (DEC owner's manual Figure 2-2)
  • Model 95 with its cover off (Rob Jarratt)
    Model 95 with its cover off (Rob Jarratt)
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 DEC, EK-A0371-OM-002, appendix D, Tables D-1 and D-2.
  2. ↑ 2.0 2.1 2.2 2.3 "MicroVAX", Wikipedia, en.wikipedia.org/wiki/MicroVAX. MicroVAX 3100 models, CPUs and clock rates, last order dates.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Digital Equipment Corporation, MicroVAX 3100 Model 85/95 Customer Technical Information, EK-A0718-TI.B01, June 1994, Tables 4-1 and 4-2 (File:MicroVAX 3100 Model 85-95 Customer Technical Information (EK-A0718-TI).pdf).
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Digital Equipment Corporation, MicroVAX 3100 and VAXserver 3100 Owner's Manual, EK-A0371-OM-002, August 1989, chapter 1, pp. 1-1 to 1-4 (File:MicroVAX 3100 and VAXserver 3100 Owner's Manual (EK-A0371-OM-002).pdf).
  5. ↑ 5.0 5.1 5.2 Malte Dehling, "DIGITAL VAXstation 3100 PSU Repair", README, github.com/mdehling/vs3100-psu-repair. Machines using the H7821-00 and H7822-00. Community source.
  6. ↑ 6.0 6.1 Peter Coghlan, "H7821 power supply in MicroVAX 3100, SCSI disk enclosures and others", cctalk mailing list, 31 January 2020, mail-archive.com.
  7. ↑ 7.0 7.1 7.2 Antonio Carlini, "Re: Is this a RIFA (uV3100-10 PSU)?", cctalk mailing list, 24 October 2022, mail-archive.com.
  8. ↑ 8.0 8.1 Rob Jarratt, "MicroVAX 3100 Model 95 Power Supply", Rob's Old Computers, 10 May 2020, robs-old-computers.com.
  9. ↑ DEC, EK-A0371-OM-002, section 2.7. Battery-backed default settings.
  10. ↑ DEC, EK-A0371-OM-002, section 6.10, p. 6-22.
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