IBM 5100 Troubleshooting Guide
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Fault finding on the IBM 5100 Portable Computer follows IBM's own maintenance library: the Maintenance Analysis Procedures (MAPs), part number 1608314, and the Maintenance Information Manual (MIM), SY31-0405-3.[1][2] The 5100 has no beep codes. It reports faults through the bring up diagnostic's letter display, the PROCESS CHECK light and numbered error codes on line 15 of the screen.
For rail tolerances, the meter check and the tape adjustments, see the IBM 5100 Maintenance Guide.
Where to start
[edit | edit source]IBM's MAPs begin every call at the start MAP (0200), which sends the engineer to the bring up or process check MAPs when the machine fails to become ready or the PROCESS CHECK light is on, and to a device MAP for a keyboard, display, tape or power failure. When several symptoms are present and PROCESS CHECK is one of them, deal with PROCESS CHECK first.[3] The MAPs are:[4]
| MAP | Covers |
|---|---|
| 0200 | Start |
| 0300 | Tape read |
| 0400 | Bring up |
| 0420 | Process check |
| 0500 | Display |
| 0510 | TV monitor |
| 0600 | Keyboard |
| 0700 | Power |
| 0810 | 5103 printer |
| 0830 | Communications/serial I/O |
| 0850 | Auxiliary tape (5106) |
| 0900 | Machine checkout |
Bring up diagnostic
[edit | edit source]The bring up diagnostic runs from executable ROS on card H2 at every power-on and whenever RESTART is pressed. It tests microinstruction processing, data transfer, the display controls, all the base logic cards, the keyboard and the display. If it completes, LOAD0 (BASIC) or CLEAR WS (APL) appears after about 25 seconds.[5]
A failure lights PROCESS CHECK or stops with a string of letters on the display. The last letter shows which test failed:[5]
| Display shows | Test | Cards and areas tested |
|---|---|---|
| Blank | (before first test) | G2, power, display |
| A | Bus in bit | F2 |
| AB | Op code test | F2, G2 |
| ABC | Read/write storage | E2 |
| ABCD | Interrupts 1, 2, 3 | C2, C4, D2, D4, E2, F2 |
| ABCDE | Device address | E2, F2, J2 |
| ABCDEF | Bus out | F2 |
| ABCDEFG | Stuck key | F2, keyboard |
| ABCDEFGH | Storage (0600 to end) | K2 to N4 |
| ABCDEFGHI | ROS content and CRC | C2, C4, D2, D4, E2 |
| ABCDEFGHIJ | ROS address read back | E2 |
| ABCDEFGHIJK | Bring up complete | H2, H4 |
The stuck-key test catches a stuck flyplate, which causes a level 3 interrupt; the diagnostic then displays the hex key code and keyboard status.[6] The card positions are mapped on the maintenance guide.
Display Registers and DCP1
[edit | edit source]With the DISPLAY REGISTERS switch in the DISPLAY REGISTERS position, the screen shows the first 512 bytes of read/write storage in hexadecimal, including the controller's registers. On a running machine all 16 lines fill with hex characters, some changing rapidly.[7] IBM's symptom index uses this: for a bring up failure on power up, go to DISPLAY REGISTERS, and if R0L0 reads 0006 the failure is in the bring up diagnostic; replace the G2 card.[8]
Diagnostic Control Program 1 (DCP1) displays and alters any read/write storage location and gives access to the ROS-resident diagnostics. To load it in normal mode, press HOLD, then hold CMD and press the minus key on the numeric keypad. Hold CMD and press plus to return to the customer's job.[9] DCP2 and the MAP diagnostic integrations (MDIs) load from IBM's diagnostic tape cartridge.[10]
Power faults
[edit | edit source]The Power MAP starts from the mains side:[11]
- With the fan not running and fuse F1 intact, check for an open line cord, power switch, AC line filter or AC box wiring, or an open fan lead J2 or a failed fan.
- If F1 blows, replace it and disconnect loads one at a time at the AC box, powering up and waiting 30 seconds each time. If F1 holds once the DC power cable is off Y1, the short is on the DC side: the MAP reconnects Y1 alone, then either removes all the cards and refits them one at a time (if F1 still blows or the power drops) or reconnects the A1 board cables one at a time.[12] If F1 still blows with the DC power cable off Y1, disconnect the power supply's AC plug; if the fuse then holds, the supply is defective. Next comes the tape motor plug (the MAP prints J1 at this step; the MIM's AC box drawings label the tape unit plug J3), then the fan plug J2. The last load removed before the fuse holds is the faulty one; if it still blows, look for a short or loose connection in the AC box.[13]
- With the fans running, calibrate the meter against the +6 V reference and measure the loaded rails on the A1 board: +5 V at A1-D13, +8.5 V at C1-C11, +12 V at C1-D13, −12 V at C1-E13.
- If any is out of tolerance, disconnect auxiliary I/O cables and Y1 and measure the unloaded voltages at the DC power cable.
Fuse F1 is 5 A 125 V on 100 V and 115 V machines and 3 A 250 V on 220 V and 235 V machines.[14] The supply shuts down on overvoltage, undervoltage or overcurrent; switch off for at least five seconds before trying again.[15]
IBM's symptom index
[edit | edit source]IBM's intermittent-failures guide records the fixes its engineers found. A selection, excluding the 5103 printer entries:[8][16]
| Symptom | Check | IBM's fix |
|---|---|---|
| Intermittent process checks and bring up failures | Power cable plug Y1 on the A1 board; a badly formed clamp lets it fall out | Reform the clamp holding Y1 |
| Process check on power up | Swap the K2 storage card with another storage card | Replace the K2 card |
| Processor checks on power up, but RESTART works | Jumpers on the A1 board | Check jumpers A1J2G07 to A1J2P08 and A1G2S07 to A1G2S09 |
| Fails to power up intermittently; fans run but no voltage to the A1 board | None | Replace the POWER ON/OFF switch |
| Fails to power up within five seconds of power down | Unplug the AC fan and tape motor plugs at the AC box and power up | If it then powers up, suspect the AC box wiring |
| No power to the A1 board | AC voltage at the output of the line filter | Replace the AC line filter |
| Card and land patterns blown on the A1 board after fitting a TV monitor | TV monitor line cord wiring putting mains on the chassis | The customer must have the monitor wiring corrected |
| Keyboard locks with a flashing cursor | Check that the last key pressed works; press RESTART to isolate it | Clean or replace the failing flyplate or key module |
| Intermittent processor checks from the keyboard | Usually when keying fast | Replace the F2 card |
| Wrong character displayed for the key pressed | None | Replace the ROS card, storage card or display card |
| Unsteady or jittering display | Connections on the brightness control | Repair the connections; otherwise replace J2 or the CRT |
| Display character distortion | Adjusting the CRT has little or no effect | Replace the J2 card |
| Blank CRT | CRT connector | The end of the cable with five wires must face the front of the machine |
| Fading CRT | None | Replace the G2 card |
| Characters larger at top left than bottom right | None | Replace the F2 and J2 cards |
| In BASIC, rows of 1s, 3s, 5s or 9s; in APL, blank CRT | None | Check jumper J2G07 to ground |
| 003 to 010 errors, intermittent | Customer and 5100 grounding | Check for an ungrounded extension cord |
| 004 and 007 errors | Loose read/write head | Replace the read/write head |
| 004, 007 and 008 errors, excessive retries | Select magnet and jackshaft adjustments (222, 223) | Adjust; if the motor locks up or does not move the tape, replace the motor |
| 007 and 008 errors | Spindle glazed by wrong contact pressure | Clean the spindle and drive rolls with isopropyl alcohol |
| 004 error, tape does not move after standing idle | Brake arms | Check that the brake arms are white |
| 012 error | Tape unit facing a window | Keep direct sunlight out of the tape drive opening |
| 007 error | Cartridge left in the drive at power on or off | Do not switch on or off with a cartridge in the drive |
| Noisy tape drive | Spindle or jackshaft bearings; noise in one direction only | Replace the bearings; for one direction, replace the jackshaft |
| "Tapes have different capacity" | All tapes hold 204K bytes; each file header takes 0.5K bytes | Allow for the headers when setting up files |
| Intermittent processor checks at halt I18 in the bring up diagnostic | Unplug the fan for no more than 15 minutes to make the fault solid | Replace the E2 card |
Tape error codes
[edit | edit source]Hardware errors appear on line 15 as ERROR xxx yzz, where xxx is the error code, y the device address and zz the subdevice address. The internal tape unit is subdevice 80 and the auxiliary tape unit 40.[17] BASIC and APL language errors are in the language reference manuals.
| Code | Meaning |
|---|---|
| 002 | Invalid command or sequence for the device, or wrong device address or file number |
| 003 | Incorrect status sensed; the latest status byte is at hex 008F |
| 004 | Time-out: data not found on tape, or a rewind took more than three minutes (load point hole not sensed) |
| 005 | Cartridge not inserted |
| 006 | File protect: the arrow points to SAFE on a write |
| 007 | Cyclic redundancy check error. A customer cartridge lasts several thousand head passes; a CE diagnostic cartridge about 500 |
| 008 | Records or files out of sequence |
| 009 | End of data read when not expected |
| 010 | End of file: read or write beyond the last record of the file |
| 011 | Specified file number not found |
| 012 | Physical end of tape: an incorrect number of files or file size |
| 013 | Tape unit not ready, or wrong device address |
| 014 | Specified subdevice not attached |
The CE diagnostic error codes run from 800 to 999 and are listed with each diagnostic routine in the MIM.[17]
Intermittent faults
[edit | edit source]IBM's general tips for making an intermittent fault show itself are to vibrate the machine, cards and connections; raise the temperature by unplugging the blower, for no more than 20 minutes; or cool parts with circuit coolant.[18] Switch the power off before removing a read/write storage card (K2 to N4); IBM allows the other cards to be pulled with power on. To isolate a fault, remove the cards and devices not involved in the failing operation: the I/O cable driver (A2), the communications cards, the APL cards (C2, D2, D4, H4) when the fault is in BASIC, the BASIC card (C4) when it is in APL, the storage cards, the 5103 printer and the 5106 tape unit.[18]
The internal and auxiliary tape units can be swapped electrically by exchanging the cable in socket Z2 of the A1 board with the one in socket B4 of the 5106.[18]
TV monitor hazard
[edit | edit source]Do not touch or remove the coaxial cable while a television used as a monitor is plugged in. If the set has not been modified correctly, 110 V can appear on the BNC connector, the cable shield and the 5100 frame.[18] IBM requires an isolation transformer and a grounded three-prong plug on any television used this way.[19]
References
[edit | edit source]- ↑ IBM, IBM 5100 Maintenance Analysis Procedures, PN 1608314, second edition (March 1976). Hosted as File:IBM 5100 Maintenance Analysis Procedures 1608314.pdf.
- ↑ IBM, IBM 5100 Maintenance Information Manual, SY31-0405-3, fourth edition (October 1979). Hosted as IBM 5100 Maintenance Information Manual.
- ↑ MAPs, pp. 100-1 and 100-2, "Using the IBM 5100 Portable Computer Maintenance Library".
- ↑ MAPs, contents, p. iii.
- ↑ 5.0 5.1 MIM, p. 3-9, "Bring Up Diagnostic".
- ↑ MIM, pp. 3-10 and 3-15, bring up diagnostic description and halts.
- ↑ MIM, p. 2-43, item 243 "Display Registers Switch", service check.
- ↑ 8.0 8.1 MIM, p. 3-90, "5100 Symptom Index".
- ↑ MIM, pp. 3-17 and 3-18, "Diagnostic Control Program 1 (DCP1)".
- ↑ MIM, p. 3-1, contents of the Diagnostic Aids section.
- ↑ MAPs, Power MAP 0700, pp. 0700-1 and 0700-2.
- ↑ MAPs, Power MAP 0700, pp. 0700-3 to 0700-5, entry points B and C.
- ↑ MIM, pp. 2-11 and 2-12, item 207 "AC Box" (J1 power supply, J2 fan, J3 tape unit).
- ↑ MIM, pp. 2-53 and 2-54, item 273 "AC Voltage Distribution".
- ↑ MIM, p. 4-51, "Power Supply Protection".
- ↑ MIM, pp. 3-91 to 3-93, "5100 Symptom Index" (continued).
- ↑ 17.0 17.1 MIM, pp. 3-60 and 3-61, "Error Codes" and "Customer Error Code Descriptions".
- ↑ 18.0 18.1 18.2 18.3 MIM, p. 3-94, "5100 Service Tips".
- ↑ MIM, p. 3-97, "Attachment of a TV Monitor".
Related pages
[edit | edit source]- IBM 5100
- IBM 5100 Maintenance Guide
- IBM 5100 Capacitor Replacement Guide
- IBM 5100 Maintenance Information Manual