IBM 3270 PC/G Maintenance Guide

3270 PC/G: 5371 system unit, 5279 Color Display on the 5278 Display Attachment Unit, and 5277 mouse (IBM photograph, 1984)

The IBM 3270 PC/G (5371 system unit with the 5278 Display Attachment Unit and 5279 Color Display) shares its PC XT-based chassis with the rest of the 3270 PC family, so the IBM 3270 PC Maintenance Guide and IBM PC XT Maintenance Guide cover the system unit. The parts unique to the PC/G are the 5278, the 5279, the Keyboard/Tablet/Mouse Adapter and the 5277 mouse.

Safety

A PC/G has two mains-powered units, the 5371 system unit and the 5279 display. The 5278 has no mains lead: IBM states that it "receives power from the 5279 display", and that the 5279 "has a 1.8-m (6-ft) power cord and requires its own power source". Unplugging the 5279 is what isolates the 5278.

1. Switch off and unplug the system unit and the 5279.
2. Discharge the reservoir capacitors in any supply you open through a resistor, and confirm with a meter.
3. Follow the CRT Discharge Procedure before working near the 5279's tube.

Do not connect or disconnect the coaxial cable to the control unit during an electrical storm.

See also Recommended Tools.

Documentation

• Introducing the IBM 3270 Personal Computer/G and /GX Work Stations (GA33-3141-0, May 1984): components, configurations, slot rules, dimensions and weights.
• IBM Personal Computer Family Service Information Manual (SA38-0037-00), chapter 10.
• IBM's service manual for the PC/G was SY33-0112, IBM 3270 Personal Computer/G: Maintenance Information for Work Stations that Use the IBM 5279 Color Display. The hosted IBM 3270 PC AT/GX Maintenance Information covers the 5378 and 5379 only.

Opening the system unit

The 5371 opens like the 5271: switch off, disconnect all cables (mains, keyboard, the 1 m cable to the 5278, the mouse or tablet and the coaxial cable), remove the five rear screws, and pull the cover forward and up.

The 5371 has six full-feature slots and two special-feature slots. IBM's standard layout puts the Display Unit Adapter in slot 1, the 3270 System Adapter in slot 2, memory in slot 3, the Keyboard/Tablet/Mouse Adapter in slot 4, the fixed disk adapter (Model 16) in slot 5, the diskette adapter in slot 6 and the printer adapter in slot 7. Features such as the IEEE-488 adapter, 64/256 KB memory option and 5161 bus extension card have fixed permitted slots; see GA33-3141-0 pp. 71-72 before moving cards.

IBM 5278 Display Attachment Unit

The 5278 is 411 mm wide, 380 mm deep and 37 mm high, weighs 8.2 kg, and can carry the 5279 on top. It provides the alphanumeric and graphics processing and the display buffer for the 5279, draws lines and fills areas in hardware, and emulates the PC Color/Graphics Monitor Adapter.

Two IBM cables connect it: 1 m to the system unit (P/N 1887792) and 680 mm to the 5279 (P/N 1887778). Check both connectors for bent pins and clean them with contact cleaner when servicing.

Model 1 (P/N 1887693) is for the 5371 and Model 2 (P/N 1887745) for the AT-based 5373. IBM warns that a Model 1 on a 5373 can cause interference on part of the screen, so check the model on a unit that has had its 5278 swapped.

IBM 5279 Color Display

The 5279 is a 14-inch display running at 720 × 512 pels, refreshed 42 times per second non-interlaced, on 100 to 127 V at 50 or 60 Hz. It weighs 18.2 kg without the optional lift stand. IBM's FRU list breaks it down only to the colour display element (P/N 1887678), power cable (5699346), monitor to DAU cable (1887778) and the two stands (1887676 tilt/swivel, 1887675 lift/tilt/swivel). Because the 5279 also powers the 5278, a fault in its supply leaves the whole graphics subsystem dead.

IBM's environmental range for the 5278 and 5279 is 15.6 to 32.2 °C and 8 to 80 % humidity in use.

Power supply checks

The 5371 uses the PC XT system board and power supply ("based on a 5160 System Unit"). IBM's limits for the same system board connectors on the 5271 are in the 3270 PC maintenance guide. Neither IBM's PC family service manual nor its PC/G introduction gives rail figures for the 5278, which takes its power from the 5279. A 44xx error points to the attachment unit and display as a pair.

5277 mouse and 5083 tablet

The 5277 is an optical mouse: it reads a printed pad of horizontal and vertical lines, so it has no ball and rollers to clean, but it needs its pad. It has three keys, measures 66 × 99 × 25 mm and weighs 168 g. One 5277 or one 5083 Tablet Model 2 can be connected at a time, through the Keyboard/Tablet/Mouse Adapter; both are options on every 5371 model. The 5083 has an active area of 292 × 292 mm, 200 lines per inch, and a four-button cursor or a stylus.

Keyboard

The PC/G uses the 3270 PC's 122-key keyboard; IBM's parts catalogue refers the 5371 keyboard to the 5271 part numbers. See the 3270 PC maintenance guide for its parts and cable.

Software and diagnostics

The Graphics Control Program is feature code 1507, P/N 1887697, and runs with PC DOS 2.1. IBM keeps the PC/G customer diagnostic diskette in the Guide to Operations at the customer site, and its engineers use that diskette. Copy the GCP and diagnostic diskettes before using them.

Related pages

• IBM 3270 PC/G
• IBM 3270 PC/G Troubleshooting Guide
• IBM 3270 PC/G Capacitor Replacement Guide
• IBM 3270 PC Maintenance Guide
• IBM 3270 PC/GX Maintenance Guide