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IBM 5100 Maintenance Guide

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IBM 5100 Portable Computer (Wikimedia Commons)

Routine care and service checks for the IBM 5100 Portable Computer, announced in September 1975, are set out in IBM's IBM 5100 Maintenance Information Manual (MIM), SY31-0405-3.[1]

Safety

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The DC supply is a switching supply. IBM describes it as "a small, high power, high frequency transistor switching regulator (TSR) supply".[2] It takes mains from the AC box through plug J1, and IBM does not draw its circuit.[3] Treat the large capacitors on the supply board as charged until measured, and discharge them through a resistor.

  • The AC box sits under the display.[4] It carries mains to the line filter, fuse F1, the power on/off switch, the fan and the tape unit motor.[3] Unplug the line cord before removing the covers.
  • IBM's display section carries the warning: "The display unit contains high voltages; therefore, use extreme caution when making internal adjustments."[5] Follow the CRT Discharge Procedure before working near the tube.
  • A domestic television used as an external monitor must be modified with an isolation transformer. IBM warns that an unmodified set can put 110 V on the coaxial cable, its shield and the 5100 frame, and tells engineers not to touch or remove the coaxial cable while such a set is plugged in.[6]

See also Battery Explosion, Capacitor or Corrosion Damage and Recommended Tools.

Documentation

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What is inside

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IBM's functional-unit drawing names the Step and Run switches, the AC box (under the display), the display, the alphameric and numeric keyboards, the power supply, the A1 board, the tape drive and the control panel.[4]

The A1 board is a card cage. The MAPs call out cards by position, so learn the map:[9][7]

IBM 5100 A1 board card positions (MIM p. 2-15)
Position Card
A2 I/O cable driver
B2 Expansion feature
C2 APL ROS 3
C4 BASIC ROS
D2 APL ROS 1
D4 APL ROS 2
E2 ROS control
F2 Base I/O
G2 Controller (the processor)
H2 BASIC, I/O and diagnostics executable ROS
H4 APL supervisor executable ROS
J2 Display
K2, K4, L2, L4, M2, M4, N2, N4 Read/write storage

Sockets along the top edge are Y1 (power) to Y4; along the bottom edge Z1 (communications/serial I/O), Z2 (tape), Z3 (display and control panel) and Z4 (keyboard).[9]

The controller card (G2) and the auxiliary tape unit adapter card carry jumpers with one position for the 5100 and another for the 5110. Check them on any card taken from a donor machine.[10]

Switch the machine off before removing a read/write storage card (K2 to N4). IBM allows the other cards to be removed with power on, and lists the cards that can be pulled to isolate a fault: the I/O cable driver, the communications cards, the APL cards when the fault is in BASIC, the BASIC card when the fault is in APL, and the storage cards.[6]

Expected measurements

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The supply produces five rails: +5, −5, +8.5, +12 and −12 V. IBM lists what each feeds:[2]

IBM 5100 DC rails and their loads (MIM p. 4-51)
Rail Loads
+5 V Basic logic voltage
−5 V Tape control card, storage cards, BSCA cards and common ROS
+8.5 V Storage cards, keyboard, display adapter, printer adapter, BSCA cards and all ROS cards
+12 V Display unit, tape select magnets, tape LEDs, BSCA cards and 5114 R1 relay
−12 V Tape unit, 5114 R1 relay, BSCA cards and asynchronous communications/serial I/O card

A supply that delivers +5 V and +12 V but not +8.5 V still leaves the ROS and storage cards unpowered, so measure all five.

IBM's tolerances at the Y1 power connector:[11]

IBM 5100 DC rail tolerances (MIM p. 2-52)
Voltage Loaded Unloaded (Y1 disconnected)
+5 V 4.6 to 5.5 5.5 to 6.5
+8.5 V 7.9 to 9.35 7.4 to 9.0
+12 V 11.0 to 13.2 9.8 to 12.2
−5 V −4.6 to −5.5 −3.7 to −4.7
−12 V −11.0 to −13.2 −9.0 to −11.5

With Y1 disconnected, IBM's +5 V range is higher than the loaded one and the +8.5, +12, −5 and −12 V ranges are lower in magnitude, so judge an unloaded supply against the unloaded column. The Power MAP measures the loaded rails on the A1 board at A1-D13 (+5 V), C1-C11 (+8.5 V), C1-D13 (+12 V) and C1-E13 (−12 V), then disconnects Y1 and measures the unloaded voltages at the DC power cable.[12] The full Y1 pin list is on the capacitor guide.

Check the meter first

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The display card (J2) provides a +6 V zener reference for checking a meter. Set the meter to its 15 V DC range, ground it at J2-D08 and measure at J2-S02. If it does not read exactly 6 V, correct each later reading with

actual voltage = 6 × measured voltage ÷ reference voltage

IBM's example: with the reference reading 5.8 V and the +5 V rail reading 4.8 V, the rail is actually 4.97 V.[13]

Protection

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The supply shuts itself down on overvoltage (+12 V output above +16 V), undervoltage (−5 V less negative than −3 V) or excessive current in the transformer primary. After any automatic shutdown, IBM says to switch the machine off for at least five seconds before powering up again.[2] IBM also states that the outputs may vary from +10 % to −9 % of rated voltage before they affect operation.[2]

Opening the machine

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Power down and unplug the line cord. Covers are item 211 and the service position item 212 in the MIM.[14] The mains wiring in the AC box is under the display.[4]

Cleaning

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  • Covers: use a mild soap or isopropyl alcohol. IBM says not to use IBM cleaning fluid on them.[15]
  • Tape head: wipe off loose dirt with a Kimwipes tissue, remove oxide with isopropyl alcohol on a Kimwipes tissue, then remove any residue with a dry one.[16]
  • Spindle roll, jackshaft rolls and drive belt: clean with isopropyl alcohol and wipe with a lint-free cloth or Kimwipes.[17] A glazed spindle causes retries and 007 and 008 tape errors.[18]
  • Keyboard PC board: clean with water and a lint-free cloth. Clean only the flyplates that are dirty or causing failures.[19]

Tape drive

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In the tape unit a belt carries motion from the motor to the jackshaft, which drives the spindle.[20] IBM's service checks and adjustments:[21]

  • Motor pulley (226): set it 0.063 ± 0.010 in (1.57 ± 0.25 mm) from the motor mounting bracket as an initial setting, then adjust with power on until the belt tracks in the centre of the pulley.
  • Jackshaft housing (223): measure the gap between the spindle and the right jackshaft roll at both ends. The two measurements must differ by less than 0.003 in (0.076 mm), or the housing needs adjusting.
  • Cartridge stops (224): adjust if the cartridge rocks, or if the gap between the stop gauge and the spindle is greater than 0.005 in (0.127 mm).
  • Tape switch assembly (221): the cartridge-in-place and file-protect switches are set 0.001 to 0.003 in (0.025 to 0.076 mm) from the cartridge.[22]

The same block of the MIM covers the forward and reverse select magnets (222), the locking wheel assembly (225), tape path and manual positioning (229), rethreading (230), the read/write head (231), the LED-PTX assembly (232) and spindle roll cleaning (233).[23] For a noisy drive, IBM's fix is to replace the spindle or jackshaft bearings, and if the noise is in one direction only, the jackshaft.[18][24]

Do not switch the 5100 on or off with a cartridge in the drive; IBM lists this as a cause of 007 errors.[18]

Keyboard

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Each key module has a flyplate that moves away from pads on the keyboard PC board when the key is pressed, reducing the capacitance at that key position.[25] Removing the keyboard PC board while a key is pressed lets the flyplate jump out of its module, so check that nothing is pressing on the keys before lifting the board.[19] IBM does not recommend refitting a dislodged flyplate, but gives the procedure (254) for when a new key module is not available.[26] A keyboard that locks with a flashing cursor usually points to the last key pressed; clean or replace its flyplate or key module.[27]

Display

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IBM supplied two types of display unit under the same part number. One has a horizontal linearity sleeve and a horizontal linearity potentiometer; the other has neither.[5]

To set brightness:[5]

  1. Set the BRIGHTNESS control on the control panel to its centre position.
  2. Press the top of the REVERSE DISPLAY switch to select a dark background.
  3. Adjust the brightness potentiometer on the display PC board until the white retrace lines just disappear.

Focus is a separate potentiometer on the display PC board. Centring and the horizontal and vertical adjustments are on pp. 2-40 and 2-41, and the Z3 socket pin assignments on p. 2-42.[28] The control-panel switches (L32-64-R32, DISPLAY REGISTERS, BASIC-APL, REVERSE DISPLAY, RESTART and lamp test, BRIGHTNESS) each have a service check on p. 2-43.[29] IBM's symptom index traces an unsteady or jittering display to the connections on the brightness control.[27]

Capacitors

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IBM's MIM, MAPs and parts catalogue give no capacitance values for the 5100. The Power MAP treats the DC supply as one field-replaceable unit, and the parts catalogue lists the AC box capacitors and the tape motor capacitor by IBM part number only.[12][8] The IBM 5100 Capacitor Replacement Guide lists the identified parts and how to record the rest.

Tools

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  • Multimeter, checked against the +6 V reference above.
  • Feeler gauges for the tape drive service checks.
  • Isopropyl alcohol and lint-free tissues.
  • Anti-static strap.
  • High-voltage probe for the display.
  • Temperature-controlled soldering iron and desoldering braid.

See Recommended Tools for general workshop equipment.

References

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  1. ↑ IBM, IBM 5100 Maintenance Information Manual, SY31-0405-3, fourth edition (October 1979). Hosted as IBM 5100 Maintenance Information Manual.
  2. ↑ 2.0 2.1 2.2 2.3 MIM, p. 4-51, "Power Supply PC Board" and "Power Supply Protection".
  3. ↑ 3.0 3.1 MIM, pp. 2-53 and 2-54, item 273 "AC Voltage Distribution" (old and new style).
  4. ↑ 4.0 4.1 4.2 MIM, p. 2-3, item 200 "5100 Portable Computer Functional Units".
  5. ↑ 5.0 5.1 5.2 MIM, p. 2-39, item 240 "Display", brightness, focus and the two display unit types.
  6. ↑ 6.0 6.1 MIM, pp. 3-94 and 3-97, "5100 Service Tips" and "Attachment of a TV Monitor".
  7. ↑ 7.0 7.1 IBM, IBM 5100 Maintenance Analysis Procedures, PN 1608314, second edition (March 1976). Hosted as File:IBM 5100 Maintenance Analysis Procedures 1608314.pdf.
  8. ↑ 8.0 8.1 IBM, IBM 5100 Portable Computer Parts Catalog, S131-0599-3, fourth edition (November 1976). Hosted as IBM 5100 Portable Computer Parts Catalog.
  9. ↑ 9.0 9.1 MIM, p. 2-15, item 209 "A1 Board (Card Locations)".
  10. ↑ MIM, p. 2-16, item 209 "A1 Board (Card Jumpers)".
  11. ↑ MIM, p. 2-52, item 272 "Power – Y1 Socket Pin Assignments", with the tolerance table.
  12. ↑ 12.0 12.1 IBM, IBM 5100 Maintenance Analysis Procedures, PN 1608314, Power MAP 0700, pp. 0700-1 and 0700-2.
  13. ↑ MIM, p. 2-49, item 270 "CE Meter Calibration Check".
  14. ↑ MIM, pp. 2-18 and 2-19, items 211 "Covers" and 212 "IBM 5100 Portable Computer Service Position".
  15. ↑ MIM, p. B-1, "Installation Procedures", cover cleaning.
  16. ↑ MIM, p. 2-36, item 231 "Read/Write Head" (removal, adjustment and cleaning).
  17. ↑ MIM, p. 2-37, item 233 "Spindle Roll Cleaning".
  18. ↑ 18.0 18.1 18.2 MIM, p. 3-92, "5100 Symptom Index".
  19. ↑ 19.0 19.1 MIM, p. 2-45, item 251 "Keyboard" (removal, disassembly and cleaning).
  20. ↑ MIM, p. D-2, glossary entry "jackshaft".
  21. ↑ MIM, pp. 2-26 to 2-30, items 223 "Jackshaft Housing", 224 "Cartridge Stops" and 226 "Motor Pulley".
  22. ↑ MIM, pp. 2-20 and 2-21, item 221 "Tape Switch Assembly".
  23. ↑ MIM, contents of section 2, p. 2-1.
  24. ↑ MIM, p. 3-93, "5100 Symptom Index".
  25. ↑ MIM, p. 4-10, keyboard operation.
  26. ↑ MIM, p. 2-47, item 254 "Flyplate Replacement".
  27. ↑ 27.0 27.1 MIM, p. 3-90, "5100 Symptom Index".
  28. ↑ MIM, pp. 2-40 to 2-42, items 240 and 241.
  29. ↑ MIM, p. 2-43, items 242 to 247.
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