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MicroVAX II Maintenance Guide

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KA630-AA CPU module (M7606), which always goes in backplane slot 1 (Phiarc, CC BY-SA 4.0)

Routine care of a MicroVAX II covers its environment, the configuration rules for the Q22-bus backplane, the power budget, the fans, the time-of-year clock battery and DEC's MicroVAX Maintenance System (MMS) diagnostics. The procedures come from DEC's MicroVAX II Maintenance Guide (AZ-GM3AA-MN), the owner's manual and the KA630-AA CPU Module User's Guide.[1][2][3] Supply work is on MicroVAX II Power Supply Guide and fault finding on MicroVAX II Troubleshooting Guide.

Environment

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MicroVAX II 630QB environmental limits (owner's manual, appendix B)
Operating Non-operating
Temperature 10–40 °C −40 to 66 °C
Temperature change 11 °C per hour –
Relative humidity 20–80% 10–95%
Altitude 2.4 km 4.9 km

[4] Reduce the maximum operating temperature by 1.8 °C for each 1,000 m of altitude.[4] The 630QB takes 88–128 V or 176–256 V at 47–63 Hz, 8.8 A typical and 12 A maximum at 120 V, and up to 690 W.[4] Use a grounded wrist strap (DEC 29-11762-00) and grounded work surface inside the enclosure.[5]

Configuration rules

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The order of modules in the backplane matters:[6]

  • The KA630-A CPU always goes in slot 1 (slot 1 of the upper BA23 frame in an H9642).
  • MS630-B memory modules go in the slots whose CD rows are interconnected with slot 1: slots 2 and 3 in the BA23-A, 2 to 4 in the BA123-A. MS630-AA modules go in the CD rows of those slots.
  • No other dual-height module may go in the CD rows of the slots reserved for memory. Leave them empty if no memory or quad-height option is fitted.
  • Total bus loads must not exceed 38 AC or 20 DC loads.[7]

Power budget

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Add up the +5 V and +12 V current of every module and drive with DEC's figures before adding options. A BA23 supply, or each regulator of a BA123, may deliver up to 36 A at +5 V and 7 A at +12 V, and no more than 230 W in total.[7]

Power used by MicroVAX II options (DEC Table 5-4, extract)
Option +5 V (A) +12 V (A) Power (W)
KA630-AA CPU (M7606) 6.2 0.14 32.7
MS630-BB memory (M7608) 1.8 0 9.0
RQDX3 controller (M7555) 2.48 0.06 13.2
TQK50 controller (M7546) 2.9 0 14.5
DEQNA Ethernet (M7504) 3.5 0.5 23.5
DHV11 multiplexer (M3104) 4.5 0.55 29.1
RD53 disk 0.9 2.5 34.5
RX50 diskette 0.85 1.8 25.9
TK50 tape 1.35 2.4 33.55

[7] In the BA23 only one RD5x fixed disk and one removable drive (RX50 or TK50) fit, and two full-height fixed disks cannot be installed because of the power limit.[8]

Fans and cooling

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The H7864 runs the BA23's front and rear fans from +10 V outputs, which a supply jumper raises to +12 V; DEC's thermal and acoustic figures assume 10 V.[9] The fans are DEC 12-17556-01, the same part front and rear.[5] Restorers find the BA23 fans noisy even at 10 V, with whine from the motors; Warner Losh noted on the cctalk list that noise can come from lubrication and that a quieter fan moving less air is a risk to components that rely on the air flow.[10][11] When refitting the BA23 rear fan, its cable is not keyed: match the curve of the connector to the curve of the fan housing.[12] The BA123 has a 12.7 cm card-cage fan and an 11.4 cm mass-storage fan, both fed with +12 V separate from the main supply outputs, and a temperature sensor above the card cage.[13][14]

Time-of-year clock battery

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The battery backup unit (DEC 12-19245-01) sits in a plastic holder on the CPU distribution insert at the rear. It keeps the KA630's time-of-year clock running with the power off, and the clock chip's RAM holds the console language. When it fails, the console stops and zeroes the clock at power-up, and the operating system finds the clock stopped and needs the time setting again.[15][3][5] To replace it in a BA23:[16]

  1. Unplug the machine.
  2. Remove the rear cover and the console cable from the CPU distribution insert.
  3. Loosen the two screws of the rear I/O panel assembly, swing it open and remove the ground strap screws.
  4. Disconnect the CPU cables from the insert, noting the red stripe on each.
  5. Disconnect the battery unit from the insert, spread the plastic holder and pop it out.

In the H9642 the insert is removed first and the battery's red and black leads are disconnected from it.[17] Check the old pack and the insert for electrolyte; see Battery Explosion, Capacitor or Corrosion Damage.

MMS diagnostics

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DEC's MMS diagnostics load from diskette or tape. Main menu selection 1, "Test the system", is a quick, non-destructive test that DEC suggests anyone can run; selection 2 lists every option the CPU recognises, with ROM revision levels, so a device that is fitted but missing from the list is at the wrong address, faulty or badly connected. The service menu (service version only) includes tests that can destroy data, and DEC reserves it for service staff after the non-destructive tests have failed to find a fault.[18]

Preventive maintenance checklist

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  1. Check the room against the environmental limits above.[4]
  2. Clean the fans and check they turn; refit the rear fan cable the right way round.[12]
  3. Check the TOY clock battery and the insert for leakage.[16]
  4. Check the module order and the power budget after any change.[6][7]
  5. Run MMS selections 1 and 2.[18]
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References

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  1. ↑ Digital Equipment Corporation, MicroVAX II Maintenance Guide, AZ-GM3AA-MN, first edition October 1985 (File:MicroVAX II Maintenance Guide (AZ-GM3AA-MN).pdf).
  2. ↑ Digital Equipment Corporation, MicroVAX II 630QB Owner's Manual, AZ-GLCAA-MN, updated May 1986 (File:MicroVAX II 630QB Owner's Manual (AZ-GLCAA-MN).pdf).
  3. ↑ 3.0 3.1 Digital Equipment Corporation, KA630-AA CPU Module User's Guide, EK-KA630-UG-001, February 1986, section 3.2.4 (File:KA630-AA CPU Module User's Guide (EK-KA630-UG-001).pdf).
  4. ↑ 4.0 4.1 4.2 4.3 DEC, AZ-GLCAA-MN, appendix B, pp. B-3 to B-4. Electrical and environmental requirements.
  5. ↑ 5.0 5.1 5.2 DEC, AZ-GM3AA-MN, section 8.1 and Table 8-1, BA23-A FRUs and ESD caution.
  6. ↑ 6.0 6.1 DEC, AZ-GM3AA-MN, sections 5.1 and 5.2. Configuration rules and module physical priority.
  7. ↑ 7.0 7.1 7.2 7.3 DEC, AZ-GM3AA-MN, sections 5.4 and 5.5, Table 5-4, pp. 5-10 to 5-13.
  8. ↑ "BA23 Enclosure", Computer History Wiki, gunkies.org/wiki/BA23_Enclosure. Mass storage limits.
  9. ↑ DEC, AZ-GM3AA-MN, section 1.4.1, p. 1-23. Fan outputs and jumper.
  10. ↑ Mark G. Thomas, "BA23 fan noise", cctalk mailing list, 31 January 2016, mail-archive.com.
  11. ↑ Warner Losh, "Re: BA23 fan noise", cctalk mailing list, 1 February 2016, mail-archive.com.
  12. ↑ 12.0 12.1 DEC, AZ-GM3AA-MN, section 8.6 and Figure 8-24, rear fan cable.
  13. ↑ DEC, AZ-GM3AA-MN, Table 9-1, BA123-A FRUs.
  14. ↑ DEC, AZ-GM3AA-MN, section 1.4.2, p. 1-28. BA123 fan and temperature sensor supply.
  15. ↑ DEC, AZ-GM3AA-MN, section 3.2.3, p. 3-11. CPU distribution insert battery backup unit.
  16. ↑ 16.0 16.1 DEC, AZ-GM3AA-MN, chapter 8, time of year clock battery backup removal, Figures 8-35 to 8-37.
  17. ↑ DEC, AZ-GM3AA-MN, section 10.3.1, p. 10-4. H9642 battery backup unit removal.
  18. ↑ 18.0 18.1 DEC, AZ-GM3AA-MN, chapter 6, sections 6.3.1 to 6.3.4.
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