Jump to content

IBM PC (5150)

From RetroTechCollection
IBM Personal Computer
IBM 5150 with a 5151 monochrome display and the 83-key keyboard
Specifications
DeveloperIBM, Boca Raton, Florida
ManufacturerIBM
TypeDesktop personal computer
Released12 August 1981 (announced)
Intro priceUS$1,565 (16 KB, no diskette drive)
CPUIntel 8088 at 4.77 MHz; socket for an Intel 8087
Memory16–64 KB on the first system board, 64–256 KB on the second; up to 640 KB with memory cards
StorageCassette port; one or two 5.25-inch diskette drives on an adapter card
DisplayOn an adapter card: MDA for the IBM 5151, or CGA for the IBM 5153, a composite monitor or a television
SoundSpeaker driven by channel 2 of the 8253 timer
OS / FirmwareIBM Cassette BASIC in ROM; IBM PC DOS on diskette
SuccessorIBM PC XT (5160)
Model no.5150

The IBM Personal Computer, machine type 5150, is IBM's Intel 8088-based personal computer announced on 12 August 1981. It was developed at IBM's laboratory in Boca Raton, Florida, and launched at US$1,565 for a machine with 16 KB of RAM and no diskette drive.[1] IBM's announcement described a system unit with 40 KB of ROM, up to 256 KB of RAM, Microsoft BASIC in ROM, a cassette port, an 83-key keyboard and five expansion slots, with the display, diskette drives and printer as options.[2]

System board

[edit | edit source]

The 8088 runs at 4.77 MHz, a third of a 14.31818 MHz crystal, and the board has a socket for an 8087 coprocessor. The support chips are an 8259A interrupt controller, an 8237A-5 DMA controller whose fourth channel refreshes the dynamic RAM, an 8253-5 timer and an 8255A-5 peripheral interface. Five 62-pin card-edge sockets carry the I/O channel, and power arrives through two six-pin connectors. Of the eight interrupt levels, six go to the expansion slots; level 0 is the timer tick and level 1 the keyboard, and the 8088's non-maskable interrupt reports memory parity errors.[3]

There is no real-time clock and no battery-backed configuration memory. Two eight-way DIP switch blocks, SW1 and SW2, tell the BIOS what is fitted: the number of diskette drives, the coprocessor, the system board memory, the display type and the memory on expansion cards.[3][4] The keyboard interface is built from the 8255A and a shift register on the system board; the keyboard's own 8048 does the scanning.[5]

Board revisions

[edit | edit source]

IBM made two system boards, named after the RAM they take.[6] The earlier board has "16KB-64KB CPU" printed on it and no mark on the rear panel; the later one has "64KB-256KB CPU" on the board and a "B" stamped on the rear panel.[4]

IBM 5150 system boards
Board marking RAM RAM chips BIOS as supplied
16KB-64KB CPU 4 banks of 16 KB 4116, which need +12 V, +5 V and −5 V 04/24/81 or 10/19/81
64KB-256KB CPU 4 banks of 64 KB 4164 10/27/82

On both boards bank 0 is soldered in and banks 1 to 3 are socketed; each bank is nine chips, eight data and one parity.[7][3] The quickest way to tell the boards apart in a photograph is the capacitors beside the parity RAM chips: the 16KB-64KB board has two beside each parity chip (for +12 V and −5 V), the 64KB-256KB board one (for +5 V).[8]

Memory and ROM

[edit | edit source]

All memory is parity-checked. The RAM chips are 250 ns access, 410 ns cycle.[3] All four system board banks are always enabled, so all four must be populated before RAM is added on an expansion card; removing the chips from a bank does not disable it.[9][4] SW2 is set to the total memory fitted; set it higher than what is fitted and the POST reports a 201 error.[7]

The board has six ROM sockets for 8 KB devices, five of them filled, for 40 KB of ROM with access time 250 ns.[3] U33 holds the BIOS; U29 to U32 hold IBM Cassette BASIC.[10]

BIOS revisions

[edit | edit source]

The BIOS revisions are identified by date (MM/DD/YY) and by the IBM part number printed on the U33 chip.[10]

IBM 5150 BIOS revisions
Date Part number Boards Notes
04/24/81 5700051 16KB-64KB Recognises at most 544 KB of RAM (it reads only the first four switches of SW2) and ignores expansion ROMs on cards, so EGA and VGA cards and hard disk controllers do not work
10/19/81 5700671 16KB-64KB The same two limitations
08/16/82 5000024 – May never have been released publicly. EGA and 5150-compatible VGA cards fail if the SW1 video switches are on-on but work at off-off
10/27/82 1501476 Both Removes the 1981 limitations. Its POST needs all four system board banks populated, with SW1 and SW2 set to match, or it miscalculates the RAM fitted

IBM sold a kit to upgrade a 16KB-64KB board to the 10/27/82 BIOS; it can only be used with all four RAM banks filled, and SW2 usually has to be reset afterwards.[8][10]

Storage and expansion

[edit | edit source]

The cassette port is a 5-pin DIN on the rear panel, used with the Cassette BASIC in ROM.[3]

Up to two internal 5.25-inch diskette drives connect to the 5-1/4 inch Diskette Drive Adapter; there is no diskette controller on the system board.[11] IBM announced the machine with 160 KB single-sided drives.[2] The earliest 5150s have a single-sided drive; later ones have a double-sided Tandon TM100-2 (or TM100-2A) or the Micropolis equivalent.[12] The IBM adapter and all three BIOS revisions fully support 160/180 KB and 320/360 KB drives, can read and write 720 KB diskettes but not format them, and do not support 1.2 MB or 1.44 MB. The drives need the IBM-type twisted floppy cable, not a hard-disk cable.[13]

There are five 8-bit expansion slots. Some 16-bit cards sold as working in an 8-bit slot mean an 8-bit slot in an AT-class machine and do not work in a 5150; others must be set to 8-bit operation by switch, jumper or software.[12]

Hard disks

[edit | edit source]

IBM offered no hard disk inside the 5150. Its 63 W power supply could not run the hard disks of the time: the start-up current of a Seagate ST-412 on +12 V exceeds the 24 W rating of the 5150 supply's +12 V line, and that is why IBM fitted a 130 W supply to the IBM PC XT (5160). IBM's hard disk option for the 5150 was the 5161 Expansion Unit, a separate box with its own supply, drive and controller.[14]

A 5150 with the 10/27/82 BIOS can run an XT-class controller such as the IBM Fixed Disk Adapter under DOS 2.0 or later. Smaller later drives draw less power; the Seagate ST-225 is reported to work on the 63 W supply. Modern XT-IDE and CompactFlash cards also need the 10/27/82 BIOS.[14]

Display

[edit | edit source]

All video is on an adapter card. The Monochrome Display and Printer Adapter drives the IBM 5151 and also carries a printer port; the Color/Graphics Monitor Adapter drives the IBM 5153, a composite monitor, or a television through an RF modulator.[2] Switches 5 and 6 of SW1 must match the card. IBM warns that both must be off when a Monochrome Display is connected and that the display can be damaged by the wrong settings or by connecting it to a colour adapter.[4] Wrong switch settings leave the adapter uninitialised, which on a 5151 gives no raster at all and looks like a dead monitor.[15]

Keyboard

[edit | edit source]

The 5150 came with the 83-key keyboard, a capacitive keyboard with its own Intel 8048 and a coiled cable to a 5-pin DIN. IBM's announcement lists the keyboard as part number 1501100.[5][2] The 84-key AT keyboard does not work on a 5150; a converter or a keyboard with an XT mode is needed.[16] The keyboard and cassette sockets are both 5-pin DIN; plugging the keyboard into the cassette socket does no damage.[9]

Power supply

[edit | edit source]

The power switch does not disconnect mains from every part inside the supply, and the supply's capacitors can hold a charge after it is unplugged.[17]

IBM rates the supply for continuous operation at 63.5 W, from 120 V ac or 220/240 V ac, with four regulated outputs.[18] Units for 110 V are usually labelled 63.5 W and units for 220 V 63 W.[17]

IBM 5150 power supply outputs (Technical Reference pp. 3-4, 3-6)
Rail Load min Load max Regulation Power Good under-voltage sense Power Good over-voltage sense
+5 V 2.3 A 7.0 A +5 % / −4 % +4.0 V +5.9 V
−5 V 0.0 A 0.3 A +10 % / −8 % −4.0 V −5.9 V
+12 V 0.4 A 2.0 A +5 % / −4 % +9.6 V +14.2 V
−12 V 0.0 A 0.25 A +10 % / −9 % −9.6 V −14.2 V

+5 V runs the system board logic and the drives and leaves about 4 A for the expansion cards. +12 V runs the dynamic memory and the diskette drive motors, on the assumption that only one drive runs at a time. All four rails are bussed to all five slots.[18] The supply also has a switched, fused ac outlet at the rear, limited to 0.75 A, on a non-standard connector meant only for the IBM Monochrome Display. The primary fuse is 2 A for 120 V and 1 A for 220/240 V. The supply shuts down all outputs if +5 V or +12 V exceeds 200 % of its maximum rated voltage, or if any output exceeds 130 % of its nominal current.[18]

Measuring the supply

[edit | edit source]

IBM's service manual gives these limits, measured at the system board and drive power connectors with the supply connected and switched on:[19]

IBM 5150 supply checks (HMS pp. 020-5 to 020-7)
Signal Meter − lead Meter + lead Reading
Power Good System board connector pin 5 Pin 1 +2.4 to +5.25 V
+5 V Pin 5 Pin 10 +4.8 to +5.25 V
−5 V (leads reversed) Pin 9 Pin 6 +4.5 to +5.40 V
+12 V Pin 7 Pin 3 +11.52 to +12.60 V
−12 V (leads reversed) Pin 4 Pin 8 +10.80 to +12.96 V
Drive +5 V Drive connector pin 2 Pin 4 +4.8 to +5.25 V
Drive +12 V Drive connector pin 3 Pin 1 +11.52 to +12.60 V

Leave the machine off for at least five seconds before switching it on again. The supply only generates Power Good after being off for five seconds, and Power Good rises 100 ms after the rails reach their sense levels; switch on too soon and the board may not start.[18][17] The supply also needs a load to start. A working system board alone, or a working full-height Tandon drive alone, is normally enough. With too little load, or with an overload, the fan turns for a second and stops, or does not turn at all.[17]

The −5 V rail

[edit | edit source]

IBM describes −5 V as the dynamic memory bias supply; it rises quickly with the other rails at power-on and decays more slowly at power-off.[18] IBM's known uses of it are the 4116 RAM on the 16KB-64KB board, chip U1 on both boards, the RAM on the IBM 32 KB and 64 KB Memory Expansion Options, and early versions of the 5-1/4 inch Diskette Drive Adapter.[17] Without −5 V (for example on a modern supply with an adapter), a 16KB-64KB board appears dead because its first RAM test fails and the POST stops silently, and a 64KB-256KB board stops with a 131 error because U1, in the cassette circuit, needs −5 V.[12]

Power-on responses and error indications

[edit | edit source]

A healthy 5150 shows a cursor after about four seconds, gives one short beep at the end of the POST and then starts Cassette BASIC or boots from diskette.[19] There is no RAM count on screen.[9] IBM's service manual sends each indication to a problem isolation chart:[19]

IBM 5150 error indications (HMS p. 010-6)
Indication IBM's chart
No beep, continuous beep or repeating short beeps Power (020)
One long and one short beep; 101 or 131 System board (100)
One long and two short beeps; one short beep with a blank or wrong display Display (400)
One short beep and Cassette BASIC appears instead of booting Diskette (600)
201; PARITY CHECK x Memory (200); a parity check can also be the power supply (020)
301, or a keyboard that does not work Keyboard (300)
601 Diskette (600)

The 10/27/82 BIOS has a bug that sends the display pattern for another fault. If a hard disk controller's ROM at C8000 is corrupted anywhere except its first two bytes, the POST should show "C800 ROM" but beeps one long and two short instead.[12]

Things that are not faults

[edit | edit source]
  • A POST card shows nothing useful: the 5150's POST does not output POST codes.[12]
  • A board that looks dead is usually not. A short-circuit tantalum capacitor on the system board, a card or a drive stops the supply (the fan may still turn), and any failed chip in RAM bank 0 also makes the board look dead. Minuszerodegrees' minimum diagnostic configuration isolates these.[12] See IBM PC (5150) Capacitor Replacement Guide.
  • A card ROM mapped anywhere from F0000 to F3FFF conflicts with the system board, which decodes that range for reads although nothing is fitted there. The card may appear to work.[12]
  • After switch-on it can take minutes for an error to appear; some hard disk controllers wait two minutes before reporting.[9]

IBM's service manual lists no preventive maintenance for the system unit, keyboard or display; the only unit it gives a maintenance task for is the IBM 80 CPS Matrix Printer.[19]

Documentation

[edit | edit source]

IBM's documents for the 5150:

General maintenance

[edit | edit source]

Cleaning, rail checks and preventive care are in IBM PC (5150) Maintenance Guide.

Capacitor replacement

[edit | edit source]

The 5150 system board and IBM's cards are decoupled with tantalum capacitors, which can fail short. See IBM PC (5150) Capacitor Replacement Guide.

Troubleshooting

[edit | edit source]

Symptom-based diagnosis is in IBM PC (5150) Troubleshooting Guide.

[edit | edit source]
  • IBM 5150 with a 5151 display and the 83-key keyboard
    IBM 5150 with a 5151 display and the 83-key keyboard
  • IBM 5150 with two diskette drives and a 5151 display
    IBM 5150 with two diskette drives and a 5151 display

References

[edit | edit source]
  1. ↑ IBM, "The IBM PC", IBM Heritage. Supports the Boca Raton development, the 12 August 1981 announcement and the US$1,565 launch price for 16 KB with no disk drive.
  2. ↑ 2.0 2.1 2.2 2.3 IBM Data Processing Division, Product Announcement: The IBM Personal Computer, 12 August 1981, PDF via minuszerodegrees.net. Supports the configuration, options and option part numbers (keyboard 1501100, Monochrome Display and Printer Adapter 1504900, 5-1/4 inch Diskette Drive Adapter 1503780, 160 KB diskette drive 1503800) and prices.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 IBM, Technical Reference, Personal Computer Hardware Reference Library, Revised Edition (April 1984), 6322507, Section 1 "System Board", pp. 1-3 to 1-15. Hosted as File:IBM PC 5150 Technical Reference.pdf, described at IBM PC 5150 Technical Reference.
  4. ↑ 4.0 4.1 4.2 4.3 IBM, Guide to Operations, Personal Computer Hardware Reference Library, Revised Edition (April 1984), 6322510, Section 5 "Options", switch setting charts pp. 5-7 to 5-50. Hosted as File:IBM PC 5150 Guide to Operations (April 1984).pdf.
  5. ↑ 5.0 5.1 IBM, Technical Reference (April 1984), Section 4 "Keyboard", pp. 4-3 to 4-4, including the keyboard interface block diagram.
  6. ↑ IBM 5150 – Motherboard Versions, minuszerodegrees.net.
  7. ↑ 7.0 7.1 IBM 5150: RAM on a 64KB-256KB motherboard and RAM on a 16KB-64KB motherboard, minuszerodegrees.net.
  8. ↑ 8.0 8.1 IBM 5150 – Early Versions, minuszerodegrees.net.
  9. ↑ 9.0 9.1 9.2 9.3 IBM 5150 – Basics, for 5150 beginners, minuszerodegrees.net.
  10. ↑ 10.0 10.1 10.2 IBM 5150 – BIOS Revisions, minuszerodegrees.net.
  11. ↑ IBM, IBM 5-1/4" Diskette Drive Adapter, Technical Reference: Options and Adapters, 6361505. Hosted as File:IBM Options and Adapters - IBM 5.25-inch Diskette Drive Adapter.pdf, described at IBM Options and Adapters - IBM 5.25-inch Diskette Drive Adapter.
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 12.6 IBM 5150 – Known Problems/Issues, minuszerodegrees.net.
  13. ↑ IBM 5150 – Floppy Drive Support, minuszerodegrees.net.
  14. ↑ 14.0 14.1 IBM 5150 – Hard Drive Support, minuszerodegrees.net.
  15. ↑ IBM 5151 – Known Problems/Issues, minuszerodegrees.net.
  16. ↑ IBM 5150 – Keyboards, minuszerodegrees.net.
  17. ↑ 17.0 17.1 17.2 17.3 17.4 IBM 5150 – Power Supply Unit (PSU), minuszerodegrees.net. Supports the mains warnings, the per-line ratings, the 63.5 W and 63 W labels, the start-up loading behaviour and IBM's known uses of −5 V.
  18. ↑ 18.0 18.1 18.2 18.3 18.4 IBM, Technical Reference (April 1984), Section 3 "Power Supply", pp. 3-3 to 3-6.
  19. ↑ 19.0 19.1 19.2 19.3 19.4 IBM, Hardware Maintenance and Service, Personal Computer Hardware Reference Library, First Edition (August 1981), 6025072. Power problem isolation chart pp. 020-4 to 020-7; normal power-on responses p. 010-5; error indications p. 010-6; parts catalogue p. 4-7; preventive maintenance p. 6-1. Hosted as File:IBM PC 5150 Hardware Maintenance and Service (August 1981).pdf. This edition describes the 16KB-64KB system board.
[edit | edit source]


Retrieved from "https://wiki.retrotechcollection.com/index.php?title=IBM_PC_(5150)&oldid=25120"