IBM 3270 PC/GX Troubleshooting Guide
.jpg)
The IBM 3270 PC/GX is a 5371 system unit, based on the PC XT, with the IBM 5378 Display Attachment Unit and 5379 Display.[1] Faults in the system unit are diagnosed as on the 3270 PC. For the 5378 and 5379, IBM's AT/GX maintenance manual gives full problem isolation charts; they were written for the AT-based 5373, whose system unit card is the Display/Mouse/Tablet Adapter, but the steps inside the 5378 and 5379 apply to the PC/GX too.[2]
Always switch the work station off with the system unit first and on with the system unit last; IBM's charts assume this order.[2]
Symptoms
[edit | edit source]| Symptom | Probable cause | Action |
|---|---|---|
| 5379 dead, no power light on the 5378 | 5378 mains supply; the 5379 takes its power from the 5378[2] | Check the outlet, the 5378 mains fuse (6 A slow-blow) and power cable, and the voltage selector switch on the rear of the 5378 supply[1][2] |
| 5378 fans not running | Fan or supply | See 5378 power supply below |
| 44xx error | The 5378 and 5379 as a pair; on the XT-based PC/GX, also the display adapter card in the system unit[1] | Work through the 5378 and 5379 checks below |
| Picture out of focus or unstable | High-voltage arcing between the two capacitors on the side of the 5379 CRT card facing away from the tube[1] | IBM's temporary fix was to separate the two capacitors as far as possible |
| New deflection card will not connect to the yoke | Deflection card P/N 4421622 does not mate with the old green XY connector (units before serial number 2585)[1] | CRT/adapter kit P/N 59X6942 (ECA037) |
| Damaged 5378 cards after a repair | Logic boards inserted the wrong way round[1] | See the orientation note in the maintenance guide |
| 2801 at POST after a long DFCA was replaced with the short card | Keyboard/Tablet/Mouse Adapter needs updating[1] | ECA040 |
| 2858 after fitting a new DFCA | Diagnostics older than level 2.40[1] | Use customer diagnostics P/N 1887728 or advanced diagnostics P/N 1887729, level 2.40 or later |
| Random characters from the keyboard after power-on | Early 5371 Keyboard/Tablet Adapter (about 1.5 inches short, no yellow wires on the solder side)[1] | Replace only if it fails |
| Picture disturbance near a 5151 second screen or a printer | Interference between units[1] | Move them apart; keep printers and plotters at least 305 mm from the display |
5378 and 5379 checks
[edit | edit source]IBM's entry procedure for the 5378 and 5379:[2]
- Remove any diskette, switch on in the correct order, and watch the screen for a minute. When the 5378 is connected to the system unit, a test pattern appears on the 5379 only when there is a failure. If one appears, listen for beeps (see below).
- If the 5378 fans are not running, check its power supply (below).
- On a colour 5379 (Model C01), check that the display's fan is running.
- Check that the video cables are in sockets J3, J4 and J5 on the rear of the 5378; the monochrome Model M01 uses J4 only.
- Unplug the video cables from the 5378 and turn the 5379's brightness control fully down. If there is no raster, the fault is in the 5379. On a colour model, a coloured raster (not white or grey) also points to the 5379.
- Press the test switch on the side of the 5379. It should show 12 to 16 white, stable vertical bars, and their brightness should follow the brightness control.
- On a colour model, hold the test switch and press the manual degauss switch: the image should waver for a few seconds. Wait at least 15 seconds before repeating.
- If the 5379 passes these tests, reconnect the video cables; the fault is in the 5378 or the system unit.
Test pattern and beeps
[edit | edit source]If a test pattern appears after power-on, IBM's chart goes by the beeps from the system unit:[2]
- No beeps: disconnect the system-unit-to-DAU cable at the 5378 end and switch on again. If the system unit now beeps, reconnect the cable, unseat the bus receiver flexi-cable from A1-D2 inside the 5378 and switch on; if there are still no beeps, replace that flexi-cable. If there were no beeps with the cable off at the 5378 end, disconnect it at the system unit end instead. If the system unit then beeps, check the cable for continuity and shorts and replace it, or failing that the adapter card in the system unit. If it still does not beep, unseat the adapter card; if the system unit then beeps, replace the adapter.
- One short beep: disconnect the cable at both ends and check pin 25 (−Display Present) for continuity; replace the cable if it is open. Then measure between pins 25 and 62 (ground) of J7 on the rear of the 5378: more than 2 ohms means a new bus receiver flexi-cable in the 5378, otherwise replace the display adapter in the system unit.
- Three or more beeps: disconnect the cable at the 5378 end. If the system unit then gives one beep, check the cable, then the bus receiver flexi-cable between J7 and the logic board; if both are good, replace the display bus receiver card, then the graphics processor card, then the system control card, then the adapter in the system unit. If it does not give one beep, disconnect the cable at the system unit end instead: one beep now means a new cable; anything else means the adapter in the system unit, then the system board.
5378 card locations
[edit | edit source]| Card | Abbreviation | Location |
|---|---|---|
| Display bus receiver | DBR | A1-D2 |
| Graphics processor | GP | A1-C2 |
| System control | SC | A1-B2 |
| Update control | UC | A1-A2 |
| Clock and video driver | CVD | B1-A2 |
| Bit plane 4/5 | BP4/5 | B1-B2 |
| Bit plane 2/3 | BP2/3 | B1-C2 |
| Bit plane 0/1 (Model C01 only) | BP0/1 | B1-D2 |
5378 power supply
[edit | edit source]The supply has four LEDs on its top.[2]
| Rail | Where to measure | Limits |
|---|---|---|
| +5 V | A1-D2D03 (ground A1-D2D08) and B1-A2D03 (ground B1-A2D08) | 4.8 to 5.2 V |
| −5.2 V | B1-A2D06 (ground B1-A2D08) | −4.9 to −5.5 V |
| +12 V | Fan connector pin C (ground pin A) | 10.8 to 13.2 V |
- All four LEDs lit, fan stopped: measure +12 V at the fan connector. Within limits, replace the fan; outside them, check continuity through the interconnect card (P3 pin 6 to fan pin C, P3 pins 7, 8, 11 and 12 to fan pin A), then replace the supply or the interconnect card.
- All four lit: check the logic board voltages in the table. If they are wrong, check continuity from the interconnect card (+5 V on P3 pins 1 to 4, −5.2 V on pin 10) before replacing the supply.
- None lit: check the outlet, the 5378 mains fuse and the mains cable before replacing the supply. If a new fuse blows, unplug the 5379's mains cable from J2 on the rear of the 5378 and try another: if it now holds, the fault is in that cable or the 5379's primary power supply assembly.[2]
Power and capacitors
[edit | edit source]The 5371 uses the PC XT system board and power supply.[1] Check its rails against IBM's limits in the 3270 PC maintenance guide, and see the IBM 3270 PC/GX Capacitor Replacement Guide for capacitor faults.
Related pages
[edit | edit source]- IBM 3270 PC/GX
- IBM 3270 PC/GX Maintenance Guide
- IBM 3270 PC/GX Capacitor Replacement Guide
- IBM 3270 PC Troubleshooting Guide
- IBM 3270 PC/G 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 IBM, IBM Personal Computer Family Service Information Manual, SA38-0037-00, 1989, hosted as IBM Personal Computer Family Service Information Manual. Chapter 10, pp. 10-5 to 10-13: PC/GX description, 5378 and 5379 power, 3270 unique error codes, and the diagnostic tips for the PC/G, PC/GX, AT/G and AT/GX, the 5371, the 5378 and the 5379.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 IBM, IBM 3270 Personal Computer AT/GX Maintenance Information, SY33-0125-1, June 1986, hosted as IBM 3270 PC AT/GX Maintenance Information. Power sequences pp. 1-17 and 1-18; 5378 and 5379 entry point and card locations pp. 3-4400-1 to 3-4400-3; test pattern and beep tables pp. 3-4400-4 to 3-4400-7; 5378 power supply tables pp. 3-4400-39 and 3-4400-40.