IBM 3270 PC Maintenance Guide
The IBM 3270 PC (machine type 5271) is maintained much like a PC XT, because its system unit is an IBM PC XT (5160): IBM's parts catalogue states that all base system parts for the 3270 XT products are the same as 5160 XT base system parts,[1] and the IBM PC XT Maintenance Guide applies to the chassis. The parts unique to the 3270 PC are the adapter cards, the keyboard and its adapter cable, the displays, and the coaxial link to the control unit.
Safety
[edit | edit source]The power supply is a 130 W switching supply on the PC XT pattern.[2] The 3270 PC version (FRU 6347754 for 120 V) differs from the standard XT supply in having a very quiet fan.[3][4] IBM closes the supply with a pop rivet or a bristle screw and replaces it as a unit.[4] Its primary side holds rectified mains. If you open it, unplug it first and discharge the reservoir capacitors through a resistor before touching anything, then confirm with a meter.
The 5272 and 5151 displays hold a high anode charge on the CRT. Follow the CRT Discharge Procedure.
IBM warns in its maintenance manual not to connect or disconnect the coaxial cable during an electrical storm.[4]
See also Recommended Tools.
Documentation
[edit | edit source]IBM manuals, with links to the hosted copies:
- IBM 3270 PC Maintenance Information (SY27-2567-2, October 1984): IBM's service manual for the 5271, with problem isolation charts, locations, removal procedures, switch settings and parts catalogue.[4]
- IBM Personal Computer Family Service Information Manual (SA38-0037-00): chapter 10 covers the 3270 PC family and chapter 18 has the parts catalogue.[1]
- IBM 3270 PC: Using the Hardware (GA23-0249-1, July 1985): setup and owner-level problem determination.[5]
- IBM 3270 Personal Computer Hints and Tips (G320-9539-0, May 1986).[3]
- IBM PC 3278/79 Emulation Adapter Technical Reference (1502336, October 1983).
On bitsavers (bitsavers.org/pdf/ibm/pc/3270/) but not hosted here: the 3270 PC Control Program User's Guide and Reference (SC23-0103-2, July 1984) and the 3270 Workstation Program User's Guide and Reference (84X0982, April 1987).
Opening the system unit
[edit | edit source]- Switch off and disconnect all cables, including the coaxial cable.
- Remove the five screws on the back of the system unit.
- Pull the cover forward and up.[4]
When refitting the cover, IBM's checklist asks for all five screws. On a colour system, check that the plastic screw covers on the top and bottom of the 5272 are in place.[4]
Card complement
[edit | edit source]Record where every card sits before removing anything. On the first three models IBM placed them as follows (slots 1 to 6 are long, 7 and 8 short):[6]
| Slot | Adapter | Models |
|---|---|---|
| 1 | 3270 System Adapter (DFCA) | 2, 4, 6 |
| 2 | 64/256 KB memory expansion | 4, 6 |
| 3 | Free | |
| 4 | Display adapter | 2, 4, 6 |
| 5 | Fixed disk adapter | 6 |
| 6 | Diskette drive adapter | 2, 4, 6 |
| 7 | Printer adapter | 4, 6 |
| 8 | Keyboard adapter | 2, 4, 6 |
Any long 3270 card can go in any long slot, but the All Points Addressable and Programmed Symbols adapters must sit either side of the display adapter, because they are joined by top-edge connectors.[3] The keyboard adapter cable plugs into the lower connector in slot 8, the leftmost slot seen from the rear.[5]
Things to check on each card:
- The keyboard adapter's ROM holds the BIOS extension for the display adapter, so the display adapter does not work without it.[7] There are three versions: the original (before 25 October 1984), a revised card with an NMI switch and a 9-pin serial port (October 1984 to early 1986), and a later card without them.[3] Models 24 and 26 use a Plasma Keyboard Adapter instead.[1]
- The display adapter is a full-length card with 8 KB of video memory and a Signetics SCN2672 controller.[7]
- Where the All Points Addressable and Programmed Symbols adapters are fitted, check the top-edge connectors that join them to the display adapter. IBM lists the top card connector as a separate FRU (P/N 8654385).[4]
- The Distributed Function Communications Adapter (DFCA) comes in two versions. The long card has a BNC coaxial connector and registers at 2D0h-2D6h; the short card that replaced it in 1986 adds a register at 2D7h.[7][3]
- Memory is on the Printer/Memory Adapter (128 KB, with an optional 256 KB piggyback), the 64/256 KB memory expansion option, or the Expanded Memory Adapter (XMA) on Models 31, 51 and 71. IBM does not support the XMA jumpered as LPT2 in a 5271 with a fixed disk, because of an interrupt level conflict.[1][3]
Power supply checks
[edit | edit source]IBM's power supply chart measures at the system board power connectors P8 and P9, numbering their pins 1 to 12 in a row. With the system unit off, connect the meter common to pin 5 and the voltage lead to pin 1, switch on, and check Power Good: it should read 2.4 to 5.2 V.[4] Then check the rails:[4]
| Rail | Meter − lead (pin) | Meter + lead (pin) | Minimum | Maximum |
|---|---|---|---|---|
| +5 V | 5 | 10 | +4.8 V | +5.2 V |
| −5 V | 9 | 6 | +4.5 V | +5.4 V |
| +12 V | 7 | 3 | +11.5 V | +12.6 V |
| −12 V | 4 | 8 | +10.8 V | +12.9 V |
The negative rails read as positive figures because the leads are reversed on them. At a diskette drive power connector the limits are +4.8 to +5.2 V (− lead pin 2, + lead pin 4) and +11.5 to +12.6 V (− lead pin 3, + lead pin 1). If any reading is out of range, IBM's chart says to replace the power supply.[4]
Keyboard and keyboard adapter cable
[edit | edit source]The 3270 PC keyboard is a 122-key Model F with 24 program function keys. The US and Canada keyboard is P/N 6110344 and the keyboard adapter cable is P/N 8654377.[4] The 1989 Service Information Manual gives P/N 1389098 as the replacement keyboard for both the metal-bottom and plastic-bottom versions.[1]
The Model F is a capacitive buckling-spring design. A sheet of foam between the switches and the top plate keeps the plates under pressure, and this foam degrades with age.[8] The 122-key keyboards use two-piece keycaps.[8]
The keyboard adapter cable joins three things: the DE-9 connector on the keyboard adapter, the round keyboard socket on the system board, and the keyboard's own cable at the light grey end.[5] It contains no electronics.[7] IBM's continuity chart gives its wiring (the signal names are from seasip.info, which worked them out from the card):[4][7]
| DE-9 pin (adapter end) | Goes to | Signal |
|---|---|---|
| 1 | System unit DIN pin 1 | XT clock |
| 2 | System unit DIN pin 2 | XT data |
| 3 | Not used | Key |
| 4 | Keyboard DIN pin 4 | Keyboard data |
| 5 | Keyboard DIN pin 5 | Keyboard clock |
| 6 | Keyboard DIN pin 1 | +5 V |
| 7 | Not used | |
| 8 | System unit DIN pin 4 | Ground |
| 9 | Keyboard DIN pin 2 | Ground |
If the continuity is good and the keyboard test still fails, IBM's chart replaces the system board; if it is not, the cable.[4] The keyboard plug is a 5-pin DIN with 240-degree pin spacing, and the keyboard uses the AT protocol and scan code set 3.[9]
A standard PC XT keyboard plugged into the system board gives POST error 302.[7]
Displays
[edit | edit source]IBM 5272 Color Display
[edit | edit source]The 5272 is a 14-inch colour monitor on a swivel stand, listed by IBM only as a complete display assembly with one part number per region (US and Canada: 6931932).[4] IBM gives the signal frequencies as 21.676 MHz video, 23.612 kHz horizontal and 62.967 Hz vertical, each ±0.02 %.[3] The display adapter tells a colour monitor from a monochrome one by pin 4 of the 9-pin connector, which a colour monitor grounds.[7] IBM's pin list gives pin 4 as signal ground tied to pin 2.[3] Follow the CRT Discharge Procedure before working inside.
IBM 5151 Monochrome Display
[edit | edit source]The 3270 PC also works with the 5151. IBM lists the 5151 fuse as 0.75 A for 120 V and 0.5 A for 220/240 V.[4] No other PC monitor or display adapter works with the 3270 PC.[3]
IBM 3295 Plasma Monitor
[edit | edit source]Fitted to Models 24 and 26 with the 3295 display adapter and the Plasma Keyboard Adapter.[1] Only Control Program 1.2.2 supports it.[3]
Coaxial cable to the control unit
[edit | edit source]The 3270 PC attaches to an IBM 3274 control unit by coaxial cable, either directly or through a 3299 multiplexer. In Distributed Function Terminal mode the 3274 needs configuration support T or D; in Control Unit Terminal mode any 3274 will do.[3][6]
IBM's DFCA problem isolation chart runs in this order:[4]
- Disconnect and reconnect the coaxial cable at the system unit and rerun the connection test. If "CONNECTED TO CONTROL UNIT" appears, the fault was a poor connection.
- If other 3270 PCs on the same control unit work, move the coaxial cable from one of them to your system unit and repeat the test. If it still fails, replace the DFCA.
- If it now connects, put both cables back and rerun the DFCA diagnostic. If it still fails, the problem is outside the 3270 PC.
- If no other 3270 PC is available, switch the system unit off, disconnect the cable, and measure between the centre pin and the shell of the system unit's BNC connector. It should read less than 1 ohm. If it does not, replace the DFCA.
Do not connect or disconnect the coaxial cable during an electrical storm.[4]
Diskette and fixed disk
[edit | edit source]The diskette drives are PC XT 360 KB drives: full-height on the early models and half-height from Model 30 onwards. Models 6 and 26 have a 10 MB fixed disk and Models 70 and 71 a 20 MB one.[1] See Floppy Drive Repair and Hard Drive Maintenance and Repair.
IBM's own advice for the fixed disk models:[3]
- Run SHUTDOWN or SHIPDISK from the diagnostics diskette to park the heads before switching off, and never move the machine while it is on.
- Format a new fixed disk with the routines on the diagnostics diskette before running FDISK and FORMAT.
- Run FDISK before FORMAT when replacing drive C: in a two-disk system. If the new drive has no DOS partition, DOS treats the second drive as C:, and formatting "C:" destroys the data on it.
Control Program
[edit | edit source]Models 31, 51 and 71 and all P models need Control Program 3.0.[1] After fitting an XMA, the Control Program 3.0 must be customised again, and the printer address jumper on the XMA set to LPT1 or LPT2.[3] The printer adapter supplied with the XT-based system unit can only be LPT1.[3]
Related pages
[edit | edit source]- IBM 3270 PC
- IBM 3270 PC Troubleshooting Guide
- IBM 3270 PC Capacitor Replacement Guide
- IBM 3270 PC/G Maintenance Guide and IBM 3270 PC/GX Maintenance Guide
- IBM PC XT Maintenance Guide
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 IBM, IBM Personal Computer Family Service Information Manual, SA38-0037-00, 1989, hosted as IBM Personal Computer Family Service Information Manual. Chapter 10, "3270 PC Products", pp. 10-1 to 10-17 (5271 models, 3270 unique error codes, diagnostic tips, ECA history); chapter 18, parts catalogue, pp. 18-33 and 18-34 (5271 FRU numbers and the note on 5160 base system parts).
- ↑ IBM, IBM Personal Computer Family Service Information Manual, SA38-0037-00, chapter 6, "5160 PC XT", p. 6-2. 130 W four-rail switching supply: +5 V 15 A ±5 %, +12 V 4.2 A ±5 %, −5 V 300 mA ±10 %, −12 V 250 mA ±10 %, with overvoltage and overcurrent shutdown.
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 W. Craig Chambers, IBM 3270 Personal Computer Hints and Tips, IBM G320-9539-0, May 1986, hosted as File:IBM 3270 PC Hints and Tips G320-9539-0.pdf. Hardware section, pp. 1-19.
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 IBM, IBM 3270 Personal Computer Maintenance Information, SY27-2567-2, October 1984, hosted as IBM 3270 PC Maintenance Information. Safety inspection checklist pp. xvii-xix; keyboard adapter cable continuity check p. 3-300-15; power supply checks pp. 3-9999-12 to 3-9999-15; DFCA charts pp. 3-2800-4 to 3-2800-11; system board and system unit locations pp. 4-100-2 and 4-100-3; parts catalogue pp. 7-7, 7-15 and 7-27.
- ↑ 5.0 5.1 5.2 IBM, IBM 3270 Personal Computer: Using the Hardware, GA23-0249-1, July 1985, hosted as File:IBM 3270 PC Using the Hardware GA23-0249-1.pdf. Keyboard setup pp. 2-17 to 2-20; POST error chart and switch settings pp. 5-11 to 5-13.
- ↑ 6.0 6.1 IBM Announcement Letter 183-129, "IBM 3270 Personal Computer", 18 October 1983 (copy at sharktastica.co.uk/resources/docs/IBM_183-129_3270PC_83.pdf). Slot allocation table for Models 2, 4 and 6.
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 John Elliott, "The IBM 5271 (aka 3270 PC)", seasip.info/VintagePC/5271.html. Keyboard adapter ROMs 6323581 and 6323582 and the video BIOS; keyboard adapter cable pinout; display adapter memory and I/O; host connect card versions; error codes 302, 3201-3203 and 2801.
- ↑ 8.0 8.1 "IBM Model F", deskthority.net wiki. Construction of the Model F, the foam sheet between the switches and top plate, and the two-piece keycaps of the 122-key PC 3270 and 3179 keyboards.
- ↑ John Elliott, "The IBM 6110344 Keyboard", seasip.info/VintagePC/ibm_6110344.html.