IBM 5120 Maintenance Guide
Preventive maintenance for the IBM 5120 Computing System follows IBM's field service manual for the machine. IBM's service documentation calls the computer the 5110 Model 3 (item 201 in the maintenance manual labels it "5110 Model X3X"), and its manual says it applies to that model only.[1] It uses the same processor card set as the IBM 5100 and IBM 5110, in a desktop case with a separate keyboard, a built-in display and two 8-inch diskette drives. The front panel carries the power switch, the BASIC/APL switch, the RESTART switch, the Display Registers/Normal switch and the display brightness control.[1]
Safety warning
[edit | edit source]Mains voltage is present inside the power supply even with the power switch off. IBM's procedure is to unplug the line cord from the wall before working on the supply.[2] The two internal diskette drives take mains through connectors P4 and P5, and IBM warns that voltage is present at those connectors whenever the machine is switched on; the diskette procedures begin by unplugging the ac drive motor cable.[3]
The supply enclosure holds two supplies, and one of them is ferroresonant, with resonant capacitor C4 on the ac side.[4] Discharge the filter capacitors on both boards and C4 through a resistor, and confirm with a meter, before touching anything in the enclosure.
The built-in display has its own high-voltage supply. Follow the CRT Discharge Procedure before working near the tube.
Documentation
[edit | edit source]- IBM 5120 Maintenance Information Manual, SY34-0192-0 (December 1979). Locations, removal and adjustment procedures, theory, diagnostics, error codes and halt codes. The scan has no text layer.
- IBM 5120 Computing System Logic Manual, SY34-0193-0 (December 1979). The hosted scan has 16 sheets, including the DC power distribution sheet 480B.
- The maintenance analysis procedures (MAPs) were a separate binder, SY34-0194, which the wiki does not hold.[1]
Power supply
[edit | edit source]Layout
[edit | edit source]The AC box holds the power switch, terminal blocks TB1 and TB2, a line filter, circuit breaker CB1 and the line cord.[5] The power supply itself carries two printed-circuit boards:[4][5][6]
- Board A2, the larger, is a transistor switching regulator (TSR) that produces the five rails for the computer. The logic manual labels it "5110 Power Supply Board A2".
- Board A1, the smaller, is a ferroresonant supply that produces +5, −5 and +24 Vdc for the internal diskette units. Each of its three outputs has its own fuse.
The DC distribution drawing at item 274 labels the two boards the other way round.[7] Item 208, the fuse procedure and the logic manual all put the fuses on A1 and terminals E1 to E14 on A2, so identify the boards by those parts.
| Fuse | Rail | Rating |
|---|---|---|
| F2 | +5 Vdc | 3 A |
| F3 | −5 Vdc | 1 A |
| F4 | +24 Vdc | 3 A |
A blown fuse on A1 points at the diskette side: a drive, its control card or its cabling. The fuses are on card PSA1 at the front of the supply; IBM's procedure removes the keyboard to reach them.[2][6]
Rails and loads
[edit | edit source]| Rail | Terminals on A2 | Loads (IBM) |
|---|---|---|
| +5 Vdc | E1, E2, E3 | Basic logic voltage |
| −5 Vdc | E13, E14 | Storage cards, BSCA cards, common ROS |
| +8.5 Vdc | E7, E8 | Storage cards, keyboard, display adapter, printer adapter, BSCA cards, all ROS cards |
| +12 Vdc | E9, E10 | BSCA cards, load resistor RL1, 5114 relay R1 |
| −12 Vdc | E11, E12 | 5114 relay R1, BSCA cards, asynchronous communications / serial I/O card |
| Ground | E4, E5, E6 |
Sources: loads from the theory section,[5] terminal positions from item 208 and logic sheet 480B.[4][6]
Expected measurements
[edit | edit source]Measure at the Y1 socket on the logic board or at E1 to E14 on board A2. IBM's limits:[8][7]
| Rail | With load (V) | No load, Y1 removed (V) | Ripple p-p (V) |
|---|---|---|---|
| +5 Vdc | 4.6 to 5.5 | 5.5 to 6.5 | 0.1 |
| −5 Vdc | −4.6 to −5.5 | −3.7 to −4.7 | 0.1 |
| +8.5 Vdc | 7.9 to 9.35 | 7.4 to 9.0 | 0.17 |
| +12 Vdc | 11.0 to 13.2 | 9.8 to 12.2 | 0.24 |
| −12 Vdc | −11.0 to −13.2 | −9.0 to −11.5 | 0.24 |
| +24 Vdc (diskette) | 22.0 to 26.4 | – | – |
IBM states that the outputs may vary from +10 % to −9 % of the rated voltage before they affect system operation.[5]
IBM's CE meter check uses the +6 Vdc zener reference on the display card: ground the meter at G2-D08 and measure G2-S02. If the meter does not read exactly 6 V, correct each later reading as 6 × measured voltage ÷ reference reading. IBM's example is a reference reading of 5.8 V and a +5 V reading of 4.8 V, which is really 4.97 V.[9]
Protection
[edit | edit source]Board A2 shuts down when the +12 Vdc output exceeds +16 Vdc, when the −5 Vdc rail is less negative than −3 Vdc, or when the current in the transformer primary is excessive. After any automatic shutdown, IBM says to switch the machine off at the power switch for at least 60 seconds before switching on again.[5] The supply also shuts down if all its loads are removed, so a bench test with nothing connected will look like a dead supply.[7]
Opening the machine
[edit | edit source]IBM's power supply removal procedure puts the supply in a service position where power checks and part replacement can be done:[2]
- Switch off and unplug the line cord from the wall.
- Remove the top and rear covers (item 200). The tabs on the rear cover locate in clips on the bottom cover.[10]
- Remove the two logic box holding screws and the two power supply holding screws.
- Slide the logic box out from the rear. Unplug the keyboard cable if the logic box will not come fully out.
- Slide the power supply out from the rear.
Go further only if the whole supply is to be replaced. Note the routing of the power supply cables before unplugging them.
Cleaning
[edit | edit source]- Covers: mild soap or isopropyl alcohol (IBM part 2200200). IBM says not to use IBM cleaning fluid on them.[11]
- Keyboard: IBM says to work cleanly, and to set the keyboard upside down on supports at least 25 mm thick with no key pressed before removing the six screws of the PC board, because removing the board with a key pressed lets the flyplate jump out of its module. Clean the PC board with water and a lint-free cloth. Clean only the flyplates that are dirty or causing failures.[12]
- Boards and vents: unplug the machine and use a soft brush and low-pressure air.
Internal diskette drives
[edit | edit source]Each internal 8-inch drive is driven by an ac motor through a belt and pulley. IBM gives removal and replacement procedures for the drive motor (item 229), the motor's capacitor (item 230) and the belt and pulley (item 231), and warns that the motor case gets hot in continuous operation and that high voltage may be present at the capacitor terminals.[13] The drives take their mains from P4 and P5 and their DC from board A1 through plugs J2 and J3, so a drive that does not spin and a drive that does not read point at different supplies.[4][6]
Do not clean the heads. IBM's note on the head/carriage assembly says it is adjusted and tested at the factory and that no part of it is to be repaired or cleaned. If the assembly is removed, put a piece of clean paper between the heads so the head surfaces do not touch.[3] The service check sets the carriage at cylinder 40 with a timing pin and checks the gap between timing pointer and timing block with feeler gauges: 0.51 mm should fit snugly and 0.53 mm should not.[3] The 3742 alignment diskette (part 2455026) listed among IBM's tools is for checking 5114 head alignment, not the internal drives.[14]
IBM's diskette timing check expects an index pulse every 166.7 ± 4.2 ms; outside that, the system reports error 001 (diskette timing error).[15] The drives can be swapped electrically, to see whether a fault follows the drive, by exchanging the two cable ends plugged into B4 and D4 of the B1 board.[16]
For general floppy drive work see Floppy Drive Repair.
5114 diskette unit
[edit | edit source]An external 5114 has its own supply and its own manual, IBM 5114 Diskette Unit Maintenance Information. Its relay R1 is fed from the 5120's +12 V and −12 V rails,[5] and the last cabled I/O device must carry a terminator; with no I/O devices attached, a terminator must be fitted at the 5120's I/O port.[7] A missing terminator causes process checks and bring-up diagnostic errors.[16]
Display
[edit | edit source]The display card G2 carries the +6 Vdc reference used for the CE meter check.[9] Discharge the CRT before working on the display or its deflection circuits; see CRT Discharge Procedure.
Capacitors
[edit | edit source]IBM's maintenance manual and logic manual give no capacitance values for the 5120's supplies; they show the boards at the level of fuses, connectors and terminals only. Read values from the parts on the board. C4 is the ac resonant capacitor of the ferroresonant supply, not an electrolytic, and must be replaced with a part of the same capacitance and ac rating. Each diskette drive's ac motor also has a capacitor (item 230), again with no value given; discharge it before disconnecting the motor leads.[13] See IBM 5120 Capacitor Replacement Guide.
Things that are not faults
[edit | edit source]- Low +12 V with the logic disconnected. The unloaded limits are 9.8 to 12.2 V, below the loaded limits.[8]
- No output at all from a supply on the bench with no load. The supply shuts down when all loads are removed.[7]
- A machine that stays dead when switched straight back on after a protection shutdown. Leave it off for 60 seconds.[5]
- A jumble of random characters on the display after a failed power-on. IBM documents this as the bring-up diagnostic halting before it cleared the screen, that is, before halt A.[17] See IBM 5120 Troubleshooting Guide.
Recommended tools
[edit | edit source]- Multimeter, checked against the +6 V reference on card G2.
- Logic probe. IBM's general logic probe (part 453212) is used on the MULTI setting for the 5120.[14]
- Feeler gauges (0.51 mm and 0.53 mm) for the head/carriage service check, and a force gauge for drive band tension.[3]
- High-voltage probe for the display.
- Isopropyl alcohol and lint-free cloths for covers and boards.
See Recommended Tools for general workshop equipment.
References
[edit | edit source]- ↑ 1.0 1.1 1.2 IBM, 5110 Model 3 Computer Maintenance Information Manual, SY34-0192-0, first edition, December 1979, preface and item 201 (pp. 2-4 to 2-5). Hosted here as IBM 5120 Maintenance Information Manual.
- ↑ 2.0 2.1 2.2 IBM, SY34-0192-0, item 271 "Power Supply", pp. 2-78 to 2-80: the danger notice that AC line voltage is present in the supply with the power switch off, the power supply removal procedure and service position, and the location of fuses F2, F3 and F4 on card PSA1 at the front of the supply.
- ↑ 3.0 3.1 3.2 3.3 IBM, SY34-0192-0, item 225 "Head/Carriage Assembly", pp. 2-26 to 2-31: the note that the assembly is adjusted and tested at the factory and must not be repaired or cleaned, the paper-between-the-heads instruction, the P4/P5 danger notice, the cylinder 40 timing-pin service check with its 0.51 mm go and 0.53 mm no-go gauge, and the drive band tension of 0.907 ± 0.113 kg set with force gauge part 460870.
- ↑ 4.0 4.1 4.2 4.3 IBM, SY34-0192-0, item 208 "Power Supply", p. 2-12: power on/off switch, AC box, PC board A1 (fuses F2 +5 Vdc, F3 −5 Vdc, F4 +24 Vdc; connectors J1, J2, J3), resonant capacitor C4, PC board A2 (inputs AC1 and AC2; output terminals E1 to E14), transformer T1, circuit breaker CB1, AC line cord, and diskette AC connectors P4 and P5.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 IBM, SY34-0192-0, "AC Power Box" and "5110-3 Power Supply", pp. 3-65 to 3-66: the AC box contents, the operating voltages, the two supplies and their rails and loads, the overvoltage, undervoltage and overcurrent protection, the 60-second off time after an automatic shutdown, the fuse on each output of the diskette supply, the +10 % / −9 % tolerance statement and the +6 Vdc reference on card G2.
- ↑ 6.0 6.1 6.2 6.3 IBM, IBM 5120 Computing System Logic Manual, SY34-0193-0, sheet 480B "DC Power Distribution": "5110 Power Supply Board A2" with output terminals E1 to E14, "5110 Power Supply Board A1" with fuses F2 (+5 Vdc 3 A), F3 (−5 Vdc 1 A) and F4 (+24 Vdc 3 A) and plugs J2 and J3 to the drive control cards, and load resistor RL1. Hosted here as IBM 5120 Computing System Logic Manual.
- ↑ 7.0 7.1 7.2 7.3 7.4 IBM, SY34-0192-0, item 274 "DC Voltage Distribution", p. 2-84: distribution drawing, voltage specifications with load, without load and peak-to-peak ripple, the +24 V limits, and the notes that the supply shuts down automatically if all loads are removed and that a terminator must be fitted at the I/O port when no I/O device is attached.
- ↑ 8.0 8.1 IBM, SY34-0192-0, item 272 "Power – Y1 Socket Pin Assignments", p. 2-81: Y1 cable to logic board pin map and the loaded and unloaded (Y1 disconnected) tolerance table.
- ↑ 9.0 9.1 IBM, SY34-0192-0, item 270 "CE Meter Calibration Check", p. 2-77, repeated in Appendix B, p. B-2.
- ↑ IBM, SY34-0192-0, item 200 "Covers", p. 2-3.
- ↑ IBM, SY34-0192-0, Appendix A, p. A-3: cover cleaning, 5110 Model 3 specifications (dimensions, 48 kg weight, power requirements and heat output) and power cord specification.
- ↑ IBM, SY34-0192-0, item 251 "Keyboard", p. 2-73: removal, disassembly, the flyplate caution and cleaning.
- ↑ 13.0 13.1 IBM, SY34-0192-0, items 229 "AC Drive Motor", 230 "Capacitor" and 231 "AC Drive Belt and Pulley", pp. 2-40 to 2-43.
- ↑ 14.0 14.1 IBM, SY34-0192-0, Appendix B "Tools and Test Equipment", pp. B-1 to B-2: general logic probe part 453212 (MULTI setting for the 5120), CE meter calibration, the 3742 alignment diskette part 2455026 for the 5114, and the diskette unit tools (force gauge 460870, thickness gauge clip 4240632, tension spring 4240631).
- ↑ IBM, SY34-0192-0, "Error Codes and Device Address Summary" and "Diskette Error Codes", pp. 4-80 to 4-81.
- ↑ 16.0 16.1 IBM, SY34-0192-0, "5120 System Service Tips", "Error Retry Bypass" and "Freelance Aids", pp. 4-99 to 4-100: read/write storage cards M2, M4, N2 and N4 to be removed only with power off, the cards and devices that can be removed to isolate a fault, swapping the internal drives electrically at B4 and D4 of the B1 board, looping the diskette read diagnostic, the ten-retry error bypass, and the caution that the last cabled I/O device must have a terminator or process checks and bring-up errors result.
- ↑ IBM, SY34-0192-0, "Bring Up Diagnostic" and "Bring Up Diagnostic Chart", pp. 4-6 to 4-7.
Related pages
[edit | edit source]- IBM 5120 · IBM 5120 Troubleshooting Guide · IBM 5120 Capacitor Replacement Guide
- IBM 5110 Maintenance Guide · IBM 5100 Maintenance Guide
- IBM 5120 Maintenance Information Manual · IBM 5120 Computing System Logic Manual · IBM 5114 Diskette Unit Maintenance Information
- CRT Discharge Procedure · Capacitor Failure Symptoms · Recommended Tools