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MicroVAX II

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MicroVAX II
DEC MicroVAX II floor-standing system (ITESM Monterrey)
MicroVAX II in a floor-standing enclosure at the Tecnológico de Monterrey (Victoroy, CC BY-SA 4.0)
Specifications
ManufacturerDigital Equipment Corporation
Type32-bit VAX minicomputer
ReleasedMay 1985[1]
CPUKA630-AA: MicroVAX 78032 with 78132 floating-point chip, 5 MHz (200 ns cycle)[1][2]
Memory1 MB on the CPU module plus MS630 modules; 9 MB maximum in DEC's 1985 guide, 16 MB in later accounts[2][1]
StorageRD51, RD52 or RD53 fixed disk; RX50 diskette; TK50 tape[3]
Display—
Sound—
PowerH7864 230 W supply (BA23); 460 W two-regulator supply (BA123)[4]
OS / FirmwareMicroVMS and VMS, ULTRIX[1][5]
PredecessorMicroVAX I[1]

The MicroVAX II is a small VAX computer that Digital Equipment Corporation introduced in May 1985, code-named Mayflower. It replaced the original MicroVAX and ran VMS (as MicroVMS), ULTRIX and other Unix systems.[1] Its processor is the KA630, a single quad-height Q22-bus module carrying the MicroVAX 78032 processor and 78132 floating-point chips, 1 MB of memory, a 64 KB boot and diagnostic ROM, the console serial line and the Q22-bus interface.[2][1] DEC aimed it at 70–110% of the performance of a VAX-11/780.[1]

DEC sold the MicroVAX II in three enclosures: the BA23, which works as a table-top, pedestal or rack-mounted box; the BA123, a movable floor-standing cabinet; and the H9642 cabinet, which holds two BA23 frames and larger disks.[6] Each has its own power supply arrangement and FRUs, so check which enclosure a machine uses before working on it. See MicroVAX II Maintenance Guide, MicroVAX II Power Supply Guide and MicroVAX II Troubleshooting Guide.

Enclosures

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MicroVAX II enclosures (DEC MicroVAX II Maintenance Guide)
Enclosure Q22-bus slots Power Notes
BA23-A 8 H7864, 230 W Table-top, pedestal or rack mount
BA123-A 12 for options (13-slot backplane) 460 W, two 230 W regulators Floor-standing, door interlock and temperature sensor
H9642 Two 8-slot backplanes Two H7864-A supplies, one per BA23 frame Cabinet for larger mass storage

[7][4][8]

Hardware

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KA630-AA processor

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The KA630-AA is the version with the floating-point chip; DEC fitted the FPU only at the factory. The module has 1 MB of on-board memory, an interval timer with 10 ms interrupts, the console serial line unit, and a Q22-bus map that lets devices DMA into all local memory. It fields Q22-bus interrupts BR7 to BR4 and supports 4 GB of virtual memory.[2] A time-of-year clock on the module is kept running by a battery backup unit on the CPU distribution insert at the rear of the machine; the clock chip's RAM also holds the user's console language.[9][10]

Four red LEDs on the module and a 7-segment display on the rear distribution insert show the progress of the power-up tests, counting down from F to 0; a green LED shows DC OK.[5] See MicroVAX II Troubleshooting Guide.

Memory

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Memory beyond the 1 MB on the CPU is on MS630 modules, which connect to the CPU through the backplane C and D rows and a 50-conductor ribbon cable.[1] DEC's 1985 maintenance guide lists the MS630-AA (dual-height), -BA and -BB, with one or two modules adding up to 8 MB for 9 MB in all; Wikipedia gives four variants up to the 8 MB MS630-CA and a 16 MB maximum.[2][7][1]

Power requirements

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Current drawn by common MicroVAX II options (DEC Table 5-4)
Option Module +5 V (A) +12 V (A)
KA630-AA CPU M7606 6.2 0.14
MS630-AA / -BA / -BB memory M7607 / M7608 / M7608 1.0 / 1.3 / 1.8 0
DEQNA Ethernet M7504 3.5 0.5
RQDX3 disk and diskette controller M7555 2.48 0.06
TQK50 tape controller M7546 2.9 0
RX50 diskette drive – 0.85 1.8
RD53 fixed disk – 0.9 2.5
TK50 tape drive – 1.35 2.4

[7] A BA23 or each BA123 regulator may supply up to 36 A at +5 V and 7 A at +12 V, but no more than 230 W in total, so both maximums cannot be drawn at once.[7]

Known problems

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  • Power supply. Restorers report H7864 failures including a blown switching transistor, and RIFA mains filter capacitors with cracked cases.[11][12] See MicroVAX II Power Supply Guide.
  • RD53 disks. Jörg Hoppe had several Micropolis 1325 drives (sold by DEC as the RD53) that spun up and then down again after about a minute; he found a weak spindle drive on one and a stuck head actuator on another.[13]
  • TOY clock battery. When the battery backup has failed, the console program stops and zeroes the clock and its RAM at power-up, and with a terminal that supports the Multinational Character Set it asks for the console language again.[10][14]

See MicroVAX II Troubleshooting Guide.

Documentation

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See MicroVAX II Documentation.

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  • KA630-AA CPU module (Phiarc, CC BY-SA 4.0)
    KA630-AA CPU module (Phiarc, CC BY-SA 4.0)
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References

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  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 "MicroVAX", Wikipedia, en.wikipedia.org/wiki/MicroVAX. Introduction date, code name, performance target, KA630-AA chips and clock, MS630 variants, operating systems, enclosures.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 DEC, AZ-GM3AA-MN, sections 3.1 and 3.2. KA630-A CPU and MS630 memory.
  3. ↑ DEC, AZ-GM3AA-MN, chapter 8, Table 8-1, BA23-A field replaceable units.
  4. ↑ 4.0 4.1 DEC, AZ-GM3AA-MN, section 1.4, pp. 1-22 to 1-29, and Table 1-1. MicroVAX II power supplies.
  5. ↑ 5.0 5.1 DEC, AZ-GM3AA-MN, chapter 7, section 7.2.1 and Table 7-1, pp. 7-1 to 7-7.
  6. ↑ Digital Equipment Corporation, MicroVAX II Maintenance Guide, AZ-GM3AA-MN, first edition October 1985, section 1.1 (File:MicroVAX II Maintenance Guide (AZ-GM3AA-MN).pdf).
  7. ↑ 7.0 7.1 7.2 7.3 DEC, AZ-GM3AA-MN, sections 5.4 to 5.6, pp. 5-10 to 5-15, Table 5-4.
  8. ↑ DEC, AZ-GM3AA-MN, chapter 9, section 9.8 and 9.9, and Table 9-1. BA123-A FRUs, door interlock and temperature sensor.
  9. ↑ DEC, AZ-GM3AA-MN, section 3.2.3, p. 3-11. CPU distribution insert and battery backup unit.
  10. ↑ 10.0 10.1 Digital Equipment Corporation, KA630-AA CPU Module User's Guide, EK-KA630-UG-001, February 1986, section 3.2.4, battery backup check (File:KA630-AA CPU Module User's Guide (EK-KA630-UG-001).pdf).
  11. ↑ Robert Jarratt, "Testing H7864 (MicroVAX II) PSU With No Load", cctalk mailing list, 1 November 2015, mail-archive.com.
  12. ↑ John H. Reinhardt, quoted in Antonio Carlini, "Re: Is this a RIFA (uV3100-10 PSU)?", cctalk mailing list, 24 October 2022, mail-archive.com.
  13. ↑ Jörg Hoppe, "Defective DEC RD53 disk drives", retrocmp.com, retrocmp.com.
  14. ↑ DEC, AZ-GM3AA-MN, section 3.2.3, power-up mode switch settings.
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