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IBM PC AT (5170)

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IBM Personal Computer AT
IBM Personal Computer AT (5170)
Specifications
ManufacturerIBM
TypeDesktop personal computer
ReleasedAnnounced 14 August 1984
CPUIntel 80286 at 6 MHz (type 1 and 2 system boards) or 8 MHz (type 3); socket for an 80287
Memory256 KB (Model 068) or 512 KB on the system board; up to 3 MB with IBM's 512 KB options
Storage1.2 MB 5.25-inch high-capacity diskette drive; 20 MB or 30 MB fixed disk
DisplayMDA, CGA, EGA or PGA adapter card
SoundSpeaker driven by the 8254-2 timer
Dimensions540 mm long, 439 mm deep, 162 mm high
Weight19.05 kg (42 lb) per IBM's service manual; 20.0 kg (44 lb) per IBM's Technical Reference
OS / FirmwareIBM PC DOS 3.0, IBM Personal Computer XENIX, PC/IX 1.1
PredecessorIBM PC XT (5160)
Model no.5170

The IBM Personal Computer AT (model 5170) is IBM's 80286-based personal computer, announced on 14 August 1984. It added a second, 36-pin connector to six of its eight expansion slots to give a 16-bit data path, a 1.2 MB high-capacity diskette drive, a battery-backed clock and configuration memory, a bidirectional keyboard interface and a keylock.[1][2]

IBM's service manual lists the AT's features as the 80286 processor, 7-channel DMA, 256 KB or 512 KB of system board RAM expandable to 3 MB with the 512 KB Memory Expansion options, eight I/O slots, a 1.2 MB diskette drive, a 20 MB or 30 MB fixed disk and a keylock.[3] The system board carries 64 KB of ROM, expandable to 128 KB, as two 32K-by-8 modules.[2]

Base models

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IBM identifies five base models by serial number:[3]

IBM 5170 base models
Model Serial number range Announced System board
068 5000000 to 5999999 August 1984 Type 1, 6 MHz, 256 KB
099 0000001 to 0999999 August 1984 Type 1, 6 MHz, 512 KB, 20 MB fixed disk
239 6000000 to 6999999 October 1985 Type 2, 6 MHz, 30 MB fixed disk
319 and 339 7000000 to 7999999 April 1986 Type 3, 8 MHz, 30 MB fixed disk

The announcement dates and boards are from minuszerodegrees' list of IBM's announcement letters.[4] The 30 MB drive is standard on Models 239, 319 and 339, and IBM sold it as an upgrade kit for Models 068 and 099 with two BIOS modules for the system board. The 84-key keyboard is used on Models 068, 099, 239 and 319; the 101-key Enhanced Keyboard is used on Model 339 only, and may be used on the 319.[3] IBM's service manual also covers the AT/370, an extended AT with System/370 processor cards.[3]

System board revisions

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IBM's documents call the three system boards type 1, type 2 and type 3.[5] The FRU part numbers are 6480170 (type 1, 256KB-512KB), 6480072 (type 2) and 6489922 (type 3).[6]

IBM 5170 system boards
Type Clock Size Main crystal RAM BIOS as supplied
1 6 MHz 13.8 × 12 in 12 MHz Stacked pairs of 41128 128K-bit chips, 150 ns or faster 01/10/84
2 6 MHz 13.8 × 9.4 in 12 MHz 41256 256K-bit chips, 150 ns or faster 06/10/85
3 8 MHz 13.8 × 9.4 in 16 MHz As type 2 11/15/85

IBM's Technical Reference gives the type 1 board as 12 by 13.8 inches with four banks of nine 128K-by-1 modules, and the type 2 board as 9.3 by 13.8 inches with two banks of nine 256K-by-1 modules, both 512 KB with parity.[2] Minuszerodegrees counts the type 1 board as two banks of 256 KB, treating each stacked pair as one position.[5] A type 1 board runs with only bank 0 populated; changing between one and two banks needs SETUP run again and may need jumper J18 moved.[5]

The memory module sockets on system boards 8286112, 6480170 and 6480072 were redesigned so that the contact surface sits below the top of the pin holes and cannot be seen from above. IBM states that they are functionally equivalent to the old style.[3]

BIOS revisions

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The BIOS, including Cassette BASIC, is 64 KB. Very early boards have four 16 KB 27128 chips in U17, U27, U37 and U47; later boards have two 32 KB 27256 chips in U27 and U47. Type 1 boards have a shunt block, U131, set for the type of ROM fitted.[7]

IBM 5170 BIOS revisions
Date Mask ROM part numbers EPROM part numbers Board
01/10/84 U27 6181028, U47 6181029 U17 6181024, U27 6181025, U37 6181026, U47 6181027 Type 1
06/10/85 U27 6480090, U47 6480091 U27 6448896, U47 6448897 Type 2
11/15/85 U27 62X0820, U47 62X0821 U27 61X9266, U47 61X9265 Type 3

IBM supported the upgrade from 01/10/84 to 06/10/85: its 30 MB fixed disk kit for type 1 machines included 06/10/85 ROMs, which the 30 MB drive needed. According to minuszerodegrees it is not known whether IBM supported an upgrade to 11/15/85, which adds 1.44 MB diskette support. The site has run that BIOS on a 6 MHz board without problems and has heard of none from others, although the BIOS was designed for an 8 MHz board.[7]

A 601 error from a replacement disk controller

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With the 06/10/85 and 11/15/85 BIOS, replacing IBM's Fixed Disk and Diskette Drive Adapter with a third-party controller can produce a 601 at POST, because those revisions look for the IBM adapter. The boot continues after an F1 prompt, although diskette operation may be affected. The 01/10/84 BIOS does not do this. A controller that the POST takes for IBM's, such as the Western Digital WD1003A-WA2, avoids it.[7]

Expansion

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Six of the eight I/O slots have both a 36-pin and a 62-pin card-edge socket; the other two have only the 62-pin socket.[2] An 8-bit card fits any slot. IBM's 128 KB and 512 KB memory options, its prototype adapter and its Fixed Disk and Diskette Drive Adapter use the 36-pin connector and do not work in other IBM PCs. IBM lists the expansion unit, the IBM Asynchronous Communications Adapter, the 64/256 KB Memory Expansion Adapter and the IBM Printer Adapter as not supported on the AT.[3] Some cards designed for the 6 MHz AT do not work in the 8 MHz model.[8]

Storage

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  • The 1.2 MB high-capacity drive reads and writes 160/180 KB, 320/360 KB and 1.2 MB diskettes. A 160/180 KB or 320/360 KB diskette written in this drive can afterwards be read reliably only in a high-capacity drive.[3] Full 1.2 MB use needs 2HC 96 tpi media.[1] IBM marked the optional 360 KB drive for the AT with an asterisk on its front, and the POST does not boot from drive B.[8]
  • The fixed disk, 20 MB or 30 MB, runs on the IBM Fixed Disk and Diskette Drive Adapter, which carries both controllers.[3]
  • The keylock disables the keyboard and locks the cover.[3] If the key is lost, IBM's procedure is to leave the unit on a flat surface, remove the five cover screws at the rear, and push a screwdriver up two to three inches into the gap between frame and cover underneath the front, in line with the lock, then pull it towards you and upwards. This lifts the cover lip over the latch. To run diagnostics in that state, remove one wire from the lock switch to enable the keyboard.[3]

Display and ports

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There is no video on the system board; the AT takes an MDA, CGA, EGA or PGA card. A switch next to the power connectors, SW1, is set to the rear for a monochrome adapter and to the front for a colour adapter. In the wrong position the POST can show "501-CRT Error" (MDA fitted) or "401-CRT Error" (CGA fitted).[9]

There are no serial or parallel ports on the system board.[2] IBM's Serial/Parallel Adapter was standard on Model 099 and optional on Model 068.[1]

Keyboard

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The AT's keyboard is a low-profile 84-key unit on a bidirectional serial interface.[2][3] It uses a new keyboard protocol, so the 83-key keyboard of the 5150 and 5160 does not work on an AT, and the AT keyboard does not work on those machines.[10] Models from 1986 were supplied with the 101-key (US) or 102-key (other countries) Enhanced Keyboard.[10]

Power supply

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Minuszerodegrees gives the rating as about 192 W.[11] IBM's dc load requirements are the same in the Technical Reference and the service manual; the two differ on the −5 V and −12 V sense levels:[2][3]

IBM 5170 dc outputs
Output Minimum load Maximum load Regulation Minimum sense level (TR p. 3-6) Minimum sense level (FSIM Figure 9-9)
+5 V 7.0 A 19.8 A +5 % / −4 % +4.5 V +4.5 V
−5 V 0 A 0.3 A +10 % / −8 % −3.75 V −4.3 V
+12 V 2.5 A 7.3 A +5 % / −4 % +10.8 V +10.8 V
−12 V 0 A 0.3 A +10 % / −9 % −10.4 V −10.2 V

The supply also provides switched 115 V or 230 V ac for the IBM Monochrome Display. The input is 100 to 125 V at up to 5 A, or 200 to 240 V at up to 3.0 A, selected by a switch above the power cord socket, with a maximum in-rush current of 100 A.[2] Heat output is 1100 BTU/hr.[3]

  • If any output is overloaded, the supply switches off within 20 ms. An overcurrent does not damage it.
  • The outputs track within 300 ms of each other at power-on and power-off, provided the minimum loads are present.
  • With no load the supply may switch off and need a power-on reset. IBM states that no damage results.
  • Power Good is generated when the supply is switched on after being off for at least one second. It has a turn-on delay of 100 to 500 ms and can drive six standard TTL loads.[2]

Load resistor

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The +12 V output needs at least 2.5 A. If no fixed disk is connected, IBM specifies a 5 ohm, 50 W load resistor on P10.[2] Its FRU number is 8286123.[6] At 12 V it draws 2.4 A. IBM does not say why the resistor is needed, and minuszerodegrees suggests that later supplies may not need it.[12]

Supplies that fail when warm

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IBM's service manual notes that some 5170 supplies fail after two or more hours powered on and then work again once the machine has been switched off and cooled. IBM's instruction is to replace the supply.[3]

Battery and the 161 error

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The configuration memory and the Motorola MC146818 real-time clock are kept alive by a battery on connector J21.[2] IBM supplied a 6 V lithium battery, FRU 8286121.[6][13] IBM's check is:[3]

  1. Switch off and remove the cover.
  2. Disconnect the battery from the system board. Measured while connected, the reading varies because of the board's drain.
  3. Set the meter to 12 V dc, common lead on pin 1 and voltage lead on pin 4 of the battery connector.
  4. Look for at least 6.0 V.

A 161 "Battery Defective or New Battery Installed" message appears on the first POST after a battery is fitted, and stays until SETUP has been run.[3][13] The first symptom of a low battery is a clock that loses time while the settings survive. The board has no charging circuit, so a rechargeable battery is pointless. Minuszerodegrees describes replacing it with four AA cells in a holder or a CR-P2 cell, considers a 3.6 V lithium cell borderline, and advises against anything above 6 V nominal because the MC146818 is rated for 3 to 6 V.[13] For leakage and clean-up, see Battery Explosion, Capacitor or Corrosion Damage.

The AT has no SETUP program in ROM.[8] IBM's service procedure runs SETUP from the Advanced Diagnostics diskette menu.[14]

Memory errors

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IBM's service manual decodes the AT's memory errors:[3]

  • PARITY CHECK 1 is a system board parity error; PARITY CHECK 2 is a Memory Expansion Adapter parity error. If the failing address is found, it is shown as a five-character code below the message; if not, five question marks.
  • In a parity check code, a first character of 0 to 3 means system board bank 0 and 4 to 7 means bank 1. Replace the 18 modules of that bank, then the system board if the same code returns. A first character of 8 or 9 means the base Memory Expansion Adapter.
  • A 10-character memory error code beginning 00 to 07 is a system board failure. The first two characters give the bank (00 to 03 bank 0, 04 to 07 bank 1) and the last four the module: 0000 is the parity module, and 0001 to 8000 are bits 0 to 15. For example, 04002 8000 is bit 15 of bank 1. Codes 08 and 09 point to the 128 KB Memory Expansion Adapter, and 10 to 37 to the 512 KB Memory Expansion Adapters.
  • If the diagnostics pass with only system board memory, refit the Memory Expansion Adapters one at a time, running SETUP each time so that the memory size is right.

Models 068 and 099 with system board 8286112, an Enhanced Graphics Adapter and the 0.5 MB to 2 MB Memory Expansion Adapter show "Parity Check 2 ?????" after a Ctrl-Alt-Del restart. IBM's fix is engineering change ECA024.[3]

Blank display and no beep: the coprocessor socket

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Some 5170 system boards were made with the math coprocessor socket fitted the wrong way round, notch to the rear. A coprocessor fitted to match that notch makes the power-on diagnostics fail with a blank display and no beep. Fitting the coprocessor with its notch towards the front of the board corrects it.[3] IBM also reminds engineers to move the coprocessor across when replacing a system board.[3]

General maintenance

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Supply checks, battery replacement, cleaning and drive care are in IBM PC AT Maintenance Guide.

Troubleshooting

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POST errors and beeps, SETUP errors, the 601 message and fixed disk faults are in IBM PC AT Troubleshooting Guide.

Capacitor replacement

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Tantalum capacitors on the system board and cards, and the power supply, are covered in IBM PC AT Capacitor Replacement Guide.

Documentation

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  • IBM Personal Computer AT (5170)
    IBM Personal Computer AT (5170)
  • Front view
    Front view
  • Rear view
    Rear view
  • Type 1 system board with the 01/10/84 BIOS ROMs 6181028 and 6181029
    Type 1 system board with the 01/10/84 BIOS ROMs 6181028 and 6181029

References

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  1. ↑ 1.0 1.1 1.2 IBM Announcement Letter 184-097, "IBM Personal Computer AT, 5170 Models 68 and 99", 14 August 1984, text via minuszerodegrees.net. Standard features, memory options up to 3 MB, the 2HC 96 tpi media, and the operating systems (PC DOS 3.0, PC/IX 1.1, IBM Personal Computer XENIX).
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 IBM, Technical Reference, Personal Computer AT, First Edition (September 1985): Section 1 "System Board", features and board sizes p. 1-3, memory p. 1-4, 8254-2 timer p. 1-22, ROM subsystem p. 1-23, MC146818 real-time clock p. 1-56, specifications p. 1-69, connectors pp. 1-71 and 1-72; Section 3 "Power Supply", pp. 3-3 to 3-7; Section 4 "Keyboard", p. 4-3. Hosted as File:IBM PC AT 5170 Technical Reference Sep85.pdf, described at IBM PC AT 5170 Technical Reference (September 1985).
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 IBM, IBM Personal Computer Family Service Information Manual, SA38-0037-00 (July 1989), Chapter 9 "5170 Personal Computer AT", pp. 9-1 to 9-11 and 9-26 to 9-27. Hosted as File:IBM Personal Computer Family Service Information Manual SA38-0037-00.pdf, described at IBM Personal Computer Family Service Information Manual.
  4. ↑ IBM 5170 – Some Documentation Pointers, minuszerodegrees.net, "IBM's Announcement Letters for the 5170".
  5. ↑ 5.0 5.1 5.2 IBM 5170 – Motherboard Versions, minuszerodegrees.net.
  6. ↑ 6.0 6.1 6.2 IBM, Hardware Maintenance Service, 6280087, Revised Edition (March 1986), "Parts (AT)", Assembly 2 "System Unit – Interior (5170)", p. 9. Hosted as File:IBM Hardware Maintenance Service 6280087 Parts Catalog (AT).pdf, described at IBM Hardware Maintenance Service (March 1986).
  7. ↑ 7.0 7.1 7.2 IBM 5170 – BIOS Revisions, minuszerodegrees.net.
  8. ↑ 8.0 8.1 8.2 IBM 5170 – Basics, for 5170 beginners, minuszerodegrees.net.
  9. ↑ IBM 5170 – Motherboard Switch/Jumper Settings, minuszerodegrees.net.
  10. ↑ 10.0 10.1 IBM 5170 – Keyboard support, minuszerodegrees.net.
  11. ↑ IBM 5170 – Power Supply Unit (PSU), minuszerodegrees.net.
  12. ↑ IBM 5170 – Load Resistor, minuszerodegrees.net.
  13. ↑ 13.0 13.1 13.2 IBM 5170 – Battery, minuszerodegrees.net.
  14. ↑ IBM, Hardware Maintenance Service, 6280087, Revised Edition (March 1986), MAP 0000 "Start (AT)", pp. 0000-1 and 0000-3. Hosted as File:IBM Hardware Maintenance Service 6280087 MAP 0000 Start (AT).pdf.
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