IBM 3270 PC Capacitor Replacement Guide
The IBM 3270 PC (machine type 5271) is a PC XT with its own keyboard, display and terminal cards. IBM describes it as "an intelligent work station based on the PC XT", and its parts catalogue states that "all base system parts for the 3270 XT products are the same as 5160 XT base system parts".[1] The capacitor work on the system board and power supply is therefore PC XT work, covered in full on the IBM PC XT Capacitor Replacement Guide. The sections below summarise it and cover the 3270-specific cards and displays.
System board
[edit | edit source]The main points, from minuszerodegrees.net:[2][3][4]
- The 5160 system board carries sixteen tantalum capacitors. Thirteen are on the +5 V line.
- The +12 V line has two components on it: C55, a ceramic, and C56, a tantalum. C56 is the one known to short. It filters only the +12 V to the expansion slots, so the board runs without it.
- The replacement value is 10 µF, rated 16 V or higher.
The 5160 power supply is a 130 W four-rail switching supply that shuts down on DC overcurrent or overvoltage.[5] A shorted tantalum therefore usually shows as a machine that will not start, although the fan may still turn.[6] The polarity convention, the three-hole footprint, the cut-and-graft soldering method and the search procedure for a short are on the IBM PC XT Capacitor Replacement Guide.
Power supply
[edit | edit source]The 5271 maintenance manual lists the system unit supply as FRU 6347754 (120 V) or 6347755 (240 V), while the 5161 Expansion Unit uses 8529247.[7] IBM's support bulletin explains the difference: the XT-based 3270 PC uses a supply with a very quiet fan (P/N 6323357, FRU 6347754), and otherwise matches the PC XT.[8] IBM published no circuit diagram or parts list for these supplies. Read the values from the parts on the board in front of you.
The line suppression capacitors on the mains input are the parts most likely to fail visibly: old RIFA types crack and release smoke with a strong, lasting smell. Replace them with parts of the same class (X2 for X2, Y2 for Y2) and at least the same voltage rating.[6]
Safety
[edit | edit source]- The supply's primary side holds rectified mains, and its reservoir capacitors can stay charged after the plug is pulled. Discharge them through a resistor and confirm with a meter before touching anything.
- IBM's safety checklist notes that a pop rivet or a bristle screw closes the supply, and that its hazard label should be intact.[7] A drilled rivet or a missing label shows that someone has been inside before you.
- IBM's checklist also requires less than 0.1 ohm between the mains plug's ground pin and the system unit frame, and the same for the monochrome display.[7] Check this before powering an unknown machine.
- The 5272, 5151 and 3295 have their own mains supplies. Follow the CRT Discharge Procedure on the CRT displays.
- Tantalums can fail with a shower of sparks or by exploding.[6] Wear eye protection when powering a board for the first time.
The 3270 adapter cards
[edit | edit source]IBM lists the 3270 cards only as whole FRUs. Its manuals give no designator maps, parts lists or schematics for any of them.[7][1]
| Card | FRU (Maintenance Information, 1984) | FRU (Service Information Manual, 1989) |
|---|---|---|
| Keyboard adapter | 8654376 | 6453624 |
| NMI keyboard adapter | 2683110 | |
| Display adapter | 8654386 (domestic), 2683125 (world trade) | 8654386 |
| All Points Addressable adapter | 8654390 | 8654390 |
| Programmed Symbols adapter | 8654381 | 8654381 |
| Distributed Function Communications Adapter (3278/79 Emulation Adapter) | 8654378 | 8665792 |
| Top card connector | 8654385 | 8654385 |
The keyboard adapter's ROM also holds the display adapter's BIOS extension, so the display does not work without it.[9] The display adapter, All Points Addressable and Programmed Symbols adapters are joined by top card connectors. IBM's removal procedure pulls the top card connector off first, then lifts the card by its top corners.[7]
Tantalum failures are common across IBM 51xx system boards and cards, and IBM's cards use the same 10 µF 16 V tantalums.[6] If the machine starts with the cards out and the supply shuts down with one particular card fitted, that card has the short. The same replacement method applies as on the system board.
A 2801 error after fitting a short DFCA is not a capacitor fault. If the host session comes up after pressing F1, the error is false and IBM's ECA001 replaces an EPROM on the keyboard/timer adapter (P/N 1497249).[1] A 3270 PC that has been converted to a plain XT and back may also have the wrong system board switches: for 3270 displays, positions 5 and 6 must be on.[1]
The displays
[edit | edit source]IBM 5272 Color Display
[edit | edit source]IBM lists the 5272 only as a complete display assembly, with one part number per region, plus the pedestal, labels and line cord. There are no internal parts in either manual, and IBM's service instructions did not allow its engineers inside the monitor.[7][1] No capacitor list for the 5272 has been published. If you open one, photograph the boards and record every value before removing anything.
IBM 5151 Monochrome Display
[edit | edit source]IBM broke the 5151 down to card level:[7]
| Part | IBM number |
|---|---|
| Analogue card | 8529233 |
| PC card | 8529234 |
| Transformer, 120 V | 8529235 |
| Transformer, 220/240 V | 8654206 |
| Fuse, 0.75 A (120 V) | 8529175 |
| Fuse, 0.5 A (220/240 V) | 8654204 |
| Signal cable | 8529173 |
| Power cable, 120 V / 220-240 V | 8529174 / 8654203 |
The manual gives no capacitor values for the 5151 either.
IBM 3295 Plasma Monitor
[edit | edit source]The 3295 is assembly 21 in IBM's parts catalogue: display power unit 6128690 (100 V) or 6128691 (200 V), display power unit fan assembly 6128693, card assembly 2720070, and panel assembly 6128480 (8269140 for world trade).[1] No component data for its power unit has been published.
What fails
[edit | edit source]John Elliott's 5271 system board failed with a blown capacitor.[9] minuszerodegrees.net finds that tantalums in IBM 51xx machines usually fail at power-on or within about 30 seconds, and much more often on boards that have been unpowered for years than on machines used regularly. Faulty tantalums often show no visible damage.[6]
Replace capacitors when:
- a capacitor on a board, card, supply or display shows visible damage;
- the supply shuts down with a particular card fitted and starts without it;
- a rail is outside IBM's limits (see the maintenance guide);
- a line suppression capacitor is cracked, discoloured or smells.
Related pages
[edit | edit source]- IBM 3270 PC
- IBM 3270 PC Maintenance Guide
- IBM 3270 PC Troubleshooting Guide
- IBM PC XT Capacitor Replacement Guide
- IBM 3270 PC/G Capacitor Replacement Guide and IBM 3270 PC/GX Capacitor Replacement Guide
- Capacitor Failure Symptoms
- CRT Discharge Procedure
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 IBM, IBM Personal Computer Family Service Information Manual, SA38-0037-00, 1989, hosted as IBM Personal Computer Family Service Information Manual. Chapter 6, p. 6-2 (5160 power supply); chapter 10, pp. 10-1 to 10-4 and 10-11 (5271 description, models, diagnostic tips, 3270 unique error codes and system board switch note); chapter 18, pp. 18-33 to 18-37 (5271 FRU numbers, note on 5160 base system parts, assembly 21 for the 3295 Plasma Monitor).
- ↑ minuszerodegrees.net, "Short-circuit on the +5 volt line of an IBM 5150/5155/5160 motherboard" (5150_5160/MDC/tantalum_short_plus_5volts.htm). Sixteen tantalums on the 5160 board, thirteen on the +5 V line.
- ↑ minuszerodegrees.net, "Short-circuit on the +12 volt line of an IBM 5150/5155/5160 motherboard" (5150_5160/MDC/tantalum_short_plus_12volts.htm). C55 (ceramic) and C56 (tantalum) on the 5160 +12 V line; C56 filters only the expansion slot +12 V and is not critical.
- ↑ minuszerodegrees.net, "IBM 51xx motherboards/cards - types that are wired to use 2-legged tantalum capacitors" (failure/). Replacement 10 µF at 16 V, or a higher voltage such as 25 V.
- ↑ IBM, IBM Personal Computer Family Service Information Manual, SA38-0037-00, chapter 6, "5160 PC XT", p. 6-2.
- ↑ 6.0 6.1 6.2 6.3 6.4 minuszerodegrees.net, "Commonly Failing Electronic Components (in vintage computers)" (failure/failure.htm). Tantalum failure modes and timing, overloaded power supply, rupturing line suppression capacitors, aluminium electrolytic replacement rules.
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 IBM, IBM 3270 Personal Computer Maintenance Information, SY27-2567-2, October 1984, hosted as IBM 3270 PC Maintenance Information. Safety checklist pp. xvii-xix; display adapter, APA and PS adapter removal pp. 5-3200-7 to 5-3200-22; parts catalogue pp. 7-7 (system unit), 7-11 (expansion unit), 7-13 (5151) and 7-15 (5272).
- ↑ W. Craig Chambers, IBM 3270 Personal Computer Hints and Tips, IBM G320-9539-0, May 1986, p. 1, hosted as File:IBM 3270 PC Hints and Tips G320-9539-0.pdf.
- ↑ 9.0 9.1 John Elliott, "The IBM 5271 (aka 3270 PC)", seasip.info/VintagePC/5271.html. Keyboard adapter ROM and video BIOS; error codes 3201-3203 and 2801; the author's 5271 system board that failed with a blown capacitor.