IBM 5110 Maintenance Guide

IBM 5110 Computing System (Wikimedia Commons)

The IBM 5110 Computing System shares its processor design, display and power supply design with the IBM 5100, and most service procedures carry across with different card positions. The procedures and figures here are IBM's, from the IBM 5110 Computer Maintenance Information Manual (MIM), SY31-0550-2, and the manuals for the IBM 5114 Diskette Unit.

Safety

The 5110's DC supply is a transistor switching regulator. It takes mains from the AC power box through plug J1, and IBM's logic manual draws it only as a block. Treat the large capacitors on the supply board as charged until measured, and discharge them through a resistor.

• The AC power box carries mains to the line filter, fuse F1, the power switch, the cooling fan and the tape unit motor. Unplug the line cord before removing covers.
• The IBM 5114 Diskette Unit has its own line cord, AC box and ferroresonant power supply. Unplug it separately.
• The display tube's high voltage is generated inside the display unit. Follow the CRT Discharge Procedure.

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

Documentation

• IBM 5110 Maintenance Information Manual, SY31-0550-2.
• IBM 5110 System Maintenance Analysis Procedures (MAPs), SY31-0553-2 (PDF). Logic card part numbers by position and model are on pp. 050-1 and 050-2, and card jumpers on p. 050-5.
• IBM 5110 System Logic Manual, SY31-0552-3.
• IBM 5114 Diskette Unit Maintenance Information, SY31-0551-1, and IBM 5114 Diskette Unit Parts Catalog, S131-0626-1.

A1 board

The processor card is in position J2 and the display card in G2, the reverse of the 5100's G2 processor and J2 display. The MIM's card map (p. 2-12) and the full table are on the IBM 5110 page. Card jumpers are listed on p. 050-5 of the MAPs.

IBM's service aids describe three jumpers on the A1 board:

• The machine check jumper connects J2-S07 to J2-S09. Removing it lets the processor keep running after a machine check, which can give misleading results.
• The basic language jumper connects H2-S04 to H2-U08 and ties the "+APL switch" line to ground.
• The Katakana check jumper connects H2-S12 to G2-P13 and is used with the Katakana display card.

Two CE switches, RUN and STEP, sit inside the machine next to the display. With RUN switched off, STEP executes one microinstruction at a time.

Expected measurements

The supply produces +5, −5, +8.5, +12 and −12 V. IBM's tolerances at the Y1 connector are:

IBM 5110 DC rail tolerances (MIM p. 2-44)

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

Unloaded, IBM's +5 V range is higher than the loaded one and the other rails' ranges are lower in magnitude. The rails can also be measured at the supply's output terminals E1 to E14, listed on the capacitor guide, or on the power connector of the I/O interface cable: pins 1 to 5 +5 V, pin 12 +8.5 V, pin 13 +12 V, pin 14 −12 V, pin 15 −5 V. The 5114 does not use the +5 V from the 5110; it makes its own and passes it on to devices attached after it.

Check the meter first

The display card (G2) provides a +6 V zener reference. Set the meter to its 15 V DC range, ground it at G2-D08 and measure at G2-S02. If it does not read exactly 6 V, correct later readings with

actual voltage = 6 × measured voltage ÷ reference voltage

IBM's example: reference 5.8 V and +5 V reading 4.8 V gives an actual 4.97 V.

Protection

The supply shuts down when +12 V exceeds +16 V, when −5 V is less negative than −3 V, or on excessive current in the transformer primary. After an automatic shutdown, switch off for at least five seconds before powering up again. The outputs may vary from +10 % to −9 % before they affect operation.

Three supplies were offered, for 100–124 V 50/60 Hz, 200–235 V 50 Hz and 235 V 50 Hz (UK). The input connection does not change with voltage, so check which supply is fitted before connecting a machine from another region.

Bring up diagnostic

The bring up diagnostic runs at every power-on and RESTART. If it completes, LOAD0 (BASIC) or CLEAR WS (APL) appears within about 25 seconds. Otherwise PROCESS CHECK lights or the display stops on a string of letters; the last letter is the failing test:

IBM 5110 bring up diagnostic (MIM p. 4-5)

Display shows	Test	Area tested
Blank	(none)	G2, power, display
A	Bus in bit test	L2, H2, J2
AB	Bus out test	A2, B2, D2, F2, H2, J2, K2, all I/O
ABC	Op code test	J2
ABCD	Read/write storage and ROS switching test	H2, J2, L2
ABCDE	Interrupt 1, 2, 3 tests	A2, B2, D2, H2, all
ABCDEF	Device address test	B2, D2, F2, H2, J2, K2, all I/O
ABCDEFG	Keyboard test	H2
ABCDEFGH	Storage test (05FF to end) and stuck key test	M2 to N4, H2, keyboard
A to J	Executable ROS initialise	L2
A to K	Executable ROS check	L2
A to L	Feature ROS check	K4
A to M	Executable ROS check	L2
A to N	Feature ROS check	K4
A to P	ROS content and CRC test	E4, F2
A to Q	Bring up complete	L2

The letters I and O are not used.

To load the Diagnostic Control Program (DCP) in diagnostic mode, hold CMD and press HOLD, hold CMD and press minus on the numeric keypad, then hold CMD and press multiply. Press C, the test number and EXECUTE. Test 0 and 1 are I/O diagnostics (internal tape without and with tape motion, or diskette read); 2 is the op code test (H2, J2); 3 the read/write storage test (M2, M4, N2, N4); 4 the ROS CRC test (E4, F2); and 5 the DCP I/O functions (A2, H2, J2, all I/O).

Tape unit (Model 1)

The tape unit service checks are items 220 to 224: jackshaft housing (220), forward and reverse select magnets (221), locking wheel assembly (222) and the tape switch assembly (224). To clean the read/write head, remove loose dirt with a Kimwipes tissue, remove oxide with isopropyl alcohol on a Kimwipes tissue, and dry with a clean one. Clean the spindle and drive rolls with isopropyl alcohol and a lint-free tissue.

The tape status byte is at storage address hex 008F:

IBM 5110 tape status byte, hex 008F (MIM p. 3-35)

Bit	0 means	1 means
0	No end of tape	End of tape (EOT)
1	Device address E response	No device address E response
2	Tape stopped	Tape running
3	No cartridge	Cartridge in place
4	Erase off	Erase on
5	LED or erase defective	LED and erase OK
6	Allow write	File protect
7	Beginning of tape (BOT)	No beginning of tape

A cartridge holds about 204,000 bytes.

IBM 5114 Diskette Unit

The 5114's drives are belt-driven from an AC motor. IBM's service checks include belt tracking (140), which requires the belt to run centred on the hub pulley and the drive pulley, the belt itself (141), the head load solenoid and bail (130), the stepper drive band (152) and diskette speed (160). IBM says not to touch or try to clean diskette surfaces; contaminated diskettes must be discarded.

The 5114 supply delivers +5 V (4.6 to 5.5 V), −5 V (−4.6 to −5.5 V) and +24 V (21.6 to 26.8 V). Ripple must not exceed 0.16 V peak to peak on ±5 V or 0.8 V on +24 V. The supply is a field-replaceable unit with no adjustments, protected by a fuse.

Keyboard and display

The display and keyboard procedures follow the 5100's; see the IBM 5100 Maintenance Guide. The 5110 display shows 16 lines of 64 characters.

Covers

Clean the covers with a mild soap or isopropyl alcohol, not IBM cleaning fluid.

Capacitors

IBM's MIM, MAPs and logic manual give no capacitance values for the 5110. The logic manual draws the 5110 DC supply as a block with output terminals (sheet 480), and the 5114 supply with designators but no values (sheet 440). IBM's Tape Read MAP names a bad tape motor start capacitor as one cause of a tape motor that will not run. See the IBM 5110 Capacitor Replacement Guide.

Related pages

• IBM 5110, IBM 5110 Troubleshooting Guide, IBM 5110 Capacitor Replacement Guide
• IBM 5100 Maintenance Guide, IBM 5120 Maintenance Guide
• CRT Discharge Procedure, Capacitor Failure Symptoms, Recommended Tools