IBM 3270 PC/G Capacitor Replacement Guide
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The IBM 3270 PC/G is an IBM 5371 system unit driving a 14-inch IBM 5279 Color Display through an IBM 5278 Display Attachment Unit. IBM states that "the 5371 System Unit is based on a 5160 System Unit for the IBM Personal Computer XT", that the 3270 PC, G and GX system board settings are the same as for the 5160, and that "all base system parts for the 3270 XT products are the same as 5160 XT base system parts".[1]
The system unit's capacitor work is therefore PC XT work, covered on the IBM PC XT Capacitor Replacement Guide: sixteen tantalums on the system board, thirteen of them on +5 V; C55 (ceramic) and C56 (tantalum) as the only components on +12 V; and 10 µF 16 V (or higher voltage) as the replacement.[2][3][4] The PC/G's adapter cards are its own (Display Unit Adapter, Keyboard/Tablet/Mouse Adapter, Printer/Memory Adapter) and are listed below.[1]
Power arrangement
[edit | edit source]A PC/G has two mains cords. IBM: "The 5278 Display Attachment Unit receives power from the 5279 display", and the 5279 "has a 1.8-m (6-ft) power cord and requires its own power source."[1]
| Unit | Mains | Fed from |
|---|---|---|
| 5371 system unit | Own power cord | |
| 5279 Color Display | Own power cord, 1.8 m | |
| 5278 Display Attachment Unit | None | The 5279 |
The 5278 measures 411 × 380 × 37 mm, weighs 8.2 kg, and connects to the system unit by a 1 m cable and to the 5279 by a 680 mm cable.[1] On the PC/GX the arrangement is reversed: the 5378 attachment unit takes the mains and powers the 5379 display.[1]
Follow the CRT Discharge Procedure before working near the 5279's tube, and treat its supply as charged until a meter shows otherwise. IBM specifies the 5279 for 100 to 127 V, 50 or 60 Hz only.[1]
IBM's parts list for the 5278 and 5279
[edit | edit source]IBM lists both units only as whole assemblies:[1]
| Unit | Part | IBM number |
|---|---|---|
| 5278 Display Attachment Unit | Model 1 DAU (for the 5371) | 1887693 |
| Model 2 DAU (for the AT-based 5373) | 1887745 | |
| Cable, DAU to system unit | 1887792 | |
| 5279 Color Display | Colour display element | 1887678 |
| Power cable | 5699346 | |
| Monitor to DAU cable | 1887778 | |
| Tilt/swivel assembly | 1887676 | |
| Lift/tilt/swivel assembly | 1887675 |
Neither IBM's PC family service manual nor its introduction to the PC/G and /GX gives a card breakdown, power supply assembly, fuse rating or capacitor values for either unit. IBM's own maintenance manual for the PC/G was SY33-0112,[5] and bitsavers' 3270 PC collection does not hold a copy.[6] No capacitor list for the 5278 or 5279 has been published. If you open one, photograph both sides of every board and record each designator, value, voltage and type before removing anything. The 5378 and 5379 of the PC/GX are documented to card level; see the IBM 3270 PC/GX Capacitor Replacement Guide.
5279 reference figures
[edit | edit source]Figures to judge a 5279 against:[1]
- 14-inch screen, viewing area 240 × 181 mm.
- 720 × 512 pels at 76 pels per inch, refreshed 42 times per second, non-interlaced.
- 80 × 32 or 80 × 49 characters, set when the Graphics Control Program is customised.
- Up to eight colours.
- 100 to 127 V, 50 or 60 Hz.
IBM advises keeping printers and plotters at least 305 mm (1 ft) from the display to avoid interference.[1]
5371 system unit
[edit | edit source]The 5371 has six full-feature slots (1 to 6) and two special-feature slots (7 and 8):[1]
| Slot | Feature | Model 12 | Model 14 | Model 16 |
|---|---|---|---|---|
| 1 | Display Unit Adapter | Yes | Yes | Yes |
| 2 | 3270 System Adapter | Yes | Yes | Yes |
| 3 | 64/256 KB memory expansion option | 128 KB | 256 KB | 192 KB |
| 4 | Keyboard/Tablet/Mouse Adapter | Yes | Yes | Yes |
| 5 | Fixed disk adapter | Yes | ||
| 6 | Diskette adapter | Yes | Yes | Yes |
| 7 | Printer Adapter or Printer/Memory Adapter | Printer Adapter | Printer Adapter | Printer/Memory Adapter (128 KB) |
| 8 | Available |
5371 FRU numbers: display adapter 8654392, DFCA 8665792, Keyboard/Tablet or Mouse Adapter 8654391, Printer/Memory Adapter 8654395, IEEE-488 adapter 8654396 and its cable 8654382, keyboard adapter cable 8654377.[1] IBM gives no component data for any of them. A card that makes the supply shut down when fitted, and not when removed, has a short; tantalums fail in IBM 51xx cards as they do on the system boards.[7]
Two documented faults are not capacitor faults:[1]
- Random characters from the keyboard after power-on, intermittently, on early 5371 units. The suspect Keyboard/Tablet Adapter cards are about 1.5 inches short of full length and have no yellow wires on the solder side; replace only if it fails.
- A false 2801 at POST after a long DFCA is replaced with a short one. The Keyboard/Tablet/Mouse Adapter needs updating under ECA040.
When to recap
[edit | edit source]On the system unit, follow the IBM PC XT Capacitor Replacement Guide: a supply that shuts down with a particular card fitted, a rail outside IBM's limits (see the 3270 PC maintenance guide), or visible tantalum damage. On the 5278 and 5279, with no published values, replace a capacitor only when it is visibly damaged or leaking, and read its value from the part itself. Line suppression capacitors that crack or smell should be replaced with parts of the same safety class.[7]
Related pages
[edit | edit source]- IBM 3270 PC/G
- IBM 3270 PC/G Maintenance Guide
- IBM 3270 PC/G Troubleshooting Guide
- IBM PC XT Capacitor Replacement Guide
- IBM 3270 PC Capacitor Replacement Guide
- IBM 3270 PC/GX Capacitor Replacement Guide
- Capacitor Failure Symptoms
- CRT Discharge Procedure
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 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 (5371 description and unit specifications, slot assignments, 5278 and 5279 specifications and power, 3270 unique error codes, diagnostic tips for the 5371); chapter 18, pp. 18-33 and 18-34 (5371, 5278 and 5279 FRU numbers; 5160 base system parts).
- ↑ minuszerodegrees.net, "Short-circuit on the +5 volt line of an IBM 5150/5155/5160 motherboard" (5150_5160/MDC/tantalum_short_plus_5volts.htm).
- ↑ minuszerodegrees.net, "Short-circuit on the +12 volt line of an IBM 5150/5155/5160 motherboard" (5150_5160/MDC/tantalum_short_plus_12volts.htm).
- ↑ minuszerodegrees.net, "IBM 51xx motherboards/cards - types that are wired to use 2-legged tantalum capacitors" (failure/). 10 µF at 16 V or higher.
- ↑ IBM, Introducing the IBM 3270 Personal Computer/G and /GX Work Stations, GA33-3141-0, May 1984, p. v, hosted as File:Introducing the IBM 3270 PC G and GX Work Stations GA33-3141-0.pdf.
- ↑ bitsavers.org, pdf/ibm/pc/3270/3270_PC directory listing (accessed 2026-10-11).
- ↑ 7.0 7.1 minuszerodegrees.net, "Commonly Failing Electronic Components (in vintage computers)" (failure/failure.htm). Tantalum failure on IBM 51xx boards and cards; rupturing line suppression capacitors.