IBM 3270 PC Troubleshooting Guide
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Fault diagnosis for the IBM 3270 PC (machine type 5271) follows IBM's own problem isolation charts in the IBM 3270 Personal Computer Maintenance Information.[1] The system board, power supply and drives are PC XT parts,[2] so the IBM PC XT Troubleshooting Guide covers them in more depth. The 3270 PC adds its own error ranges: 28xx for the coaxial adapter and 32xx for the display adapter and its graphics options.[2]
Preliminary checks
[edit | edit source]A good POST gives three responses. The memory count appears in the top left corner and rises in 16 KB steps to the installed amount; one short beep sounds; then the operating system starts, or IBM Personal Computer BASIC appears if there is no diskette and no bootable fixed disk.[1] Anything else is a POST failure. Note the first error message; IBM says to work on the first one when there are several, and pressing F1 continues past it.[1]
IBM's POST error chart sends each indication to a problem isolation chart (PIC):[1]
| Indication | Area | What to do |
|---|---|---|
| No beep, continuous beep, or repeating short beeps | Undetermined | Check the power supply first (see below), then the system board |
| Memory size wrong or not shown (screen not blank) | Memory | Check memory switches and the memory adapters |
| Blank, wrong or unreadable screen with any beep | Display | See No display below |
| 1xx | System board | As for a PC XT |
| xxxxx xx 201, or any parity check | Memory | As for a PC XT; the memory option switch settings for the 3270 PC adapters are in the Service Information Manual, pp. 10-13 and 10-14 |
| 3xx or 03xx | Keyboard | See Keyboard faults below |
| 601 | Diskette drive | As for a PC XT |
| 17xx | Fixed disk | As for a PC XT |
| 18xx | Expansion unit | Switch on the 5161 before the system unit; check its cable |
| 28xx | DFCA | See Host connection faults below |
| 32xx | Display adapter | See Display adapter and graphics options below |
| xxxxx (ROM address) | ROM | See ROM errors below |
The owner's guide adds one symptom that is easy to miss: one long and two short beeps with a correct screen can mean the system board switches are set wrongly.[3] The correct settings are:[3]
| Switch | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|
| Setting | Off | Off with coprocessor, On without | Off | Off | On | On | Off for two diskette drives, On for one | On |
Switches 5 and 6 both on is the setting IBM requires for the 3270 displays.[2] The owner's guide prints the settings as 0 and 1; they are shown here as Off and On to match the Service Information Manual.
Power supply
[edit | edit source]IBM's chart measures at the system board connectors P8 and P9, with their pins numbered 1 to 12. Power Good (meter common on pin 5, voltage lead on pin 1) should read 2.4 to 5.2 V.[1]
| 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 |
If a reading is out of range, IBM's action is to replace the power supply.[1] Before doing that, disconnect the cards and drives: a shorted tantalum capacitor on the system board or an adapter overloads the supply, which then will not run although its fan may turn.[4] Thirteen of the sixteen tantalums on the 5160 system board are on the +5 V line, and minuszerodegrees.net finds that they usually fail at power-on or within about 30 seconds.[4] A line suppression capacitor in the supply that ruptures gives smoke and a strong smell.[4]
No display
[edit | edit source]The display adapter's BIOS extension is in the ROM on the keyboard adapter, so the display adapter does not work unless the keyboard adapter is fitted and working.[5] Check it first on a machine with no picture.
IBM's display check for a colour system:[1]
- Check that the display's power indicator is lit.
- If it is not, check the display's power switch, test the outlet with a lamp and check the power cord for continuity.
- If all of those are good, the display is faulty.
The adapter tells a colour monitor from a monochrome one by pin 4 of the display connector, which a colour monitor grounds.[5] Only the 5272 and 5151 work with the 3270 PC; standard PC display adapters and other monitors do not.[6]
Display adapter and graphics options
[edit | edit source]On the 5271, 3201 points to the display adapter, 3202 to the Programmed Symbols adapter and 3203 to the All Points Addressable adapter.[5] IBM's 32xx table also includes the top card connector that joins the three cards.[2]
The diagnostics diskette tests the Programmed Symbols memory in about four minutes and the All Points Addressable memory in about three.[1]
- A 3268 or 3288 error sends you to the top card connectors. Reseat them; if they were seated, check their continuity and replace any that fail. If they are good, replace the display adapter, then the option card.[1]
- Any other 32xx from these tests points at the option card itself. IBM notes that the diagnostic checks all of the font or display memory, and advises replacing the card only if the error affects your applications.[1]
The display adapter test shows the PC character set and the MFI (host) character set for comparison by eye; if either is wrong, IBM replaces the display adapter.[1]
Keyboard faults
[edit | edit source]- Error 302 with a standard PC XT keyboard is expected: the 3270 PC wants its own 122-key keyboard. Press F1 to continue.[5]
- Error 302 with the 3270 keyboard points at the keyboard or the keyboard adapter cable, according to the owner's guide.[3]
- The keyboard adapter cable joins the DE-9 connector in slot 8, the system board keyboard socket and the keyboard cable.[3] IBM's continuity chart is reproduced in the maintenance guide. If the cable is good and the keyboard test still fails, IBM replaces the system board.[1]
- On units built before 25 October 1984, Enter and the black arrow keys work only when the Control Program is loaded. That is the original keyboard adapter, not a fault.[6]
Host connection faults
[edit | edit source]A 28xx error, or the diagnostic message "ERROR-NOT CONNECTED TO CONTROL UNIT", leads to IBM's DFCA chart:[1]
- Disconnect and reconnect the coaxial cable and rerun the connection test.
- If other 3270 PCs on the same control unit work, try one of their cables. If yours still fails, replace the DFCA; if it now connects, the problem is outside the 3270 PC.
- Otherwise switch off, remove the cable and measure between the centre pin and shell of the system unit's BNC connector. Less than 1 ohm is correct; anything else means replacing the DFCA.
Do not connect or disconnect the coaxial cable during an electrical storm.[1]
A 2801 can be false. If a long DFCA has been replaced with the short one, press F1 after POST; if the host session then comes up, the 2801 is false. IBM's ECA001 supplies an EPROM (P/N 1497249) for the keyboard/timer adapter to cure it.[2]
In Distributed Function Terminal mode the 3274 needs configuration support T or D. Control Unit Terminal mode works with any 3274 but gives only one host session.[7]
Memory and XMA
[edit | edit source]- The XMA diagnostic uses D000-DFFF. Any other adapter with RAM or ROM in that range causes a false 8505.[2]
- IBM does not support the XMA jumpered as LPT2 in a 5271 with a fixed disk, because of an interrupt level conflict.[2]
- The display adapter uses memory segment A, so memory above 640 KB in that segment does not work on a 3270 PC.[6]
ROM errors
[edit | edit source]A five-digit ROM address at POST identifies the failing ROM:[1]
| Error code | Action |
|---|---|
| C0000 | Replace the keyboard/timer adapter |
| CA000 | Replace the keyboard/timer adapter |
| C8000 | Replace the fixed disk adapter |
| F0000 to FC000 | Replace the system board |
C0000 and CA000 are the areas where the keyboard adapter maps its ROM.[5]
Fixed disk
[edit | edit source]Replacing drive C: in a two-disk system needs care: run FDISK before FORMAT, because a drive with no DOS partition is skipped and the second drive becomes C:.[6] Park the heads with SHUTDOWN or SHIPDISK from the diagnostics diskette before moving the machine.[6]
Diagnostics diskette
[edit | edit source]The 3270 PC diagnostics diskette offers: 0, run diagnostic routines; 2, format diskette; 3, prepare system for relocation; 9, exit to system diskette.[1] Its diagnostic error chart uses the same code ranges as POST, and a code ending in 00 means the device passed.[1]
Related pages
[edit | edit source]- IBM 3270 PC
- IBM 3270 PC Maintenance Guide
- IBM 3270 PC Capacitor Replacement Guide
- IBM PC XT Troubleshooting Guide
- IBM 3270 PC/G Troubleshooting Guide and IBM 3270 PC/GX Troubleshooting Guide
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 IBM, IBM 3270 Personal Computer Maintenance Information, SY27-2567-2, October 1984, hosted as IBM 3270 PC Maintenance Information. POST responses pp. 2-5 to 2-7 and 3-10-1 to 3-10-3; POST error chart pp. 3-15-1 to 3-15-3; display check p. 3-25-1 onwards; diagnostics menu p. 3-90-2; diagnostic error chart and ROM error table pp. 3-95-1 to 3-95-3; keyboard adapter cable continuity p. 3-300-15; DFCA charts pp. 3-2800-4 to 3-2800-11; display adapter charts pp. 3-3200-11 to 3-3200-28; power supply checks pp. 3-9999-12 to 3-9999-15.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 IBM, IBM Personal Computer Family Service Information Manual, SA38-0037-00, 1989, hosted as IBM Personal Computer Family Service Information Manual. Chapter 10, pp. 10-3, 10-4, 10-11 and 10-12: 3270 unique error codes, false 2801, XMA notes; chapter 18, p. 18-34: 5160 base system parts.
- ↑ 3.0 3.1 3.2 3.3 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. POST error chart and switch settings, pp. 5-11 to 5-13; keyboard setup, pp. 2-17 to 2-20.
- ↑ 4.0 4.1 4.2 minuszerodegrees.net, "Commonly Failing Electronic Components (in vintage computers)" (failure/failure.htm) and "Short-circuit on the +5 volt line of an IBM 5150/5155/5160 motherboard" (5150_5160/MDC/tantalum_short_plus_5volts.htm).
- ↑ 5.0 5.1 5.2 5.3 5.4 John Elliott, "The IBM 5271 (aka 3270 PC)", seasip.info/VintagePC/5271.html. Keyboard adapter ROM holding the video BIOS; monitor sense on pin 4; error codes 302, 3201-3203 and 2801.
- ↑ 6.0 6.1 6.2 6.3 6.4 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.
- ↑ 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). Host attachment modes.