Editing IBM PC AT (5170)

{{Infobox computer
| name          = IBM Personal Computer AT
| logo          = [[File:IBM PC AT 5170 badge.svg|150px]]
| image         = [[File:IBM PC AT 5170.jpg|260px]]
| caption       = IBM Personal Computer AT (5170)
| developer     = IBM Entry Systems Division, Boca Raton
| manufacturer  = IBM
| type          = Desktop personal computer
| release date  = August 1984
| discontinued  = 1987
| cpu           = Intel 80286 @ 6 MHz (type 1 and 2 boards) or 8 MHz (type 3); optional Intel 80287
| memory        = 256 KB or 512 KB on the system board; IBM supports expansion to 3 MB with its own 512 KB options
| storage       = 1.2 MB 5.25" high-capacity diskette drive; optional 20 MB or 30 MB fixed disk
| display       = MDA, CGA, EGA or PGA on an adapter card
| sound         = Speaker driven by the 8254 timer
| dimensions    = 540 mm L &times; 439 mm D &times; 162 mm H
| weight        = 19.05 kg (42 lb) per IBM's service manual; 20.0 kg (44 lb) per IBM's Technical Reference
| os            = IBM PC DOS 3.0 and later; OS/2 1.x; IBM and SCO Xenix; PC/IX
| predecessor   = [[IBM PC XT (5160)]]
| successor     = IBM Personal System/2
| model         = 5170
}}

The '''IBM Personal Computer AT''' (model '''5170''') moved the IBM PC line to the '''Intel 80286''', introduced the '''16-bit AT bus''' that was later standardised as ISA, and replaced the DIP switches and one-way keyboard protocol of the [[IBM PC (5150)|5150]] and [[IBM PC XT (5160)|5160]] with a battery-backed clock and configuration memory and a bidirectional keyboard.

IBM's own service manual summarises the machine as: 80286 processor, 7-channel DMA, 128 KB ROM, 256 KB or 512 KB of system-board RAM expandable to 3 MB with IBM's 512 KB Memory Expansion options, eight I/O slots, a 1.2 MB high-capacity diskette drive, a 20 MB or 30 MB fixed disk and a keylock.<ref name="fsim">IBM, ''IBM Personal Computer Family Service Information Manual'', SA38-0037-00 &mdash; hosted on this wiki as [[IBM Personal Computer Family Service Information Manual]]. Chapter 9 "5170 Personal Computer AT": Figure 9-1 (features), the base-model serial-number ranges, Figure 9-2 (specifications, including 162 &times; 540 &times; 439 mm and 19.05 kg, 1100 BTU/hr heat output and the electrical ranges), Figure 9-7 (input protection), Figure 9-8 (dc load requirements), Figure 9-9 (sense levels), the locked-cover removal procedure, the power-supply thermal-failure tip, the battery voltage check at the battery connector, the reversed math-coprocessor socket that gives a blank display and no beep, the parity check 1 and 2 distinction, the 10-character memory error code bank/module decode, ECA024 for the Parity Check 2 message on models 068 and 099, and the redesigned memory-module sockets on system boards P/N 8286112, 6480170 and 6480072.</ref>

== Base Models ==

IBM recognises five base models, and they are told apart by '''serial number range''':<ref name="fsim" />

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+'''IBM 5170 base models'''
! Model !! Serial number range
|-
| 068 || 5000000 &ndash; 5999999
|-
| 099 || 0000001 &ndash; 0999999
|-
| 239 || 6000000 &ndash; 6999999
|-
| 319 / 339 || 7000000 &ndash; 7999999
|}

An '''AT/370''' variant, carrying System/370 emulation hardware, is documented separately in the same manual.<ref name="fsim" />

== System Board Revisions ==

Three revisions exist, which IBM's documentation calls type 1, type 2 and type 3:<ref name="mzat">minuszerodegrees.net pages for the IBM 5170: [https://www.minuszerodegrees.net/5170/motherboard/5170_motherboard_revisions.htm Motherboard Versions] for the type 1, 2 and 3 boards with their speeds, form factors, crystals, RAM types and the jumper J18 note; [https://www.minuszerodegrees.net/5170/bios/5170_bios_revisions.htm BIOS Revisions] for the three BIOS dates, the mask-ROM and EPROM part numbers, the U131 shunt block, the IBM-supported 01/10/84 to 06/10/85 upgrade through the 30 MB hard drive kit, and the 601 POST error produced by the two 1985 BIOS revisions when the IBM Fixed Disk and Diskette Drive Adapter is not found; [https://www.minuszerodegrees.net/5170/psu/5170_psu.htm Power Supply] for the approximate 192 W rating and the minimum loading; and [https://www.minuszerodegrees.net/5170/misc/5170_load_resistor.htm Load Resistor] for the 5 ohm 50 W resistor drawing 2.4 A from the +12 V line.</ref>

{| class="wikitable styled-table" style="width:95%; text-align:center;"
|+'''IBM 5170 system board revisions'''
! Type !! Clock !! Form factor !! Main crystal !! RAM !! BIOS as supplied
|-
| 1 || 6 MHz || 13.8" &times; 12" || 12 MHz || Stacked/piggybacked 41128 128K-bit chips, 150 ns or faster || 01/10/84
|-
| 2 || 6 MHz || 13.8" &times; 9.4" || 12 MHz || 41256 256K-bit chips, 150 ns or faster || 06/10/85
|-
| 3 || 8 MHz || 13.8" &times; 9.4" || 16 MHz || As type 2 || 11/15/85
|}

IBM's ''Technical Reference'' describes the memory arrangement by bank: the '''type 1''' board has four banks of nine 128K-by-1 modules, and the '''type 2''' board has two banks of nine 256K-by-1 modules &mdash; both totalling 512 KB with parity.<ref name="trat">IBM, ''IBM Personal Computer AT Technical Reference'' (September 1985) &mdash; hosted on this wiki as [[:File:IBM PC AT 5170 Technical Reference Sep85.pdf]] and documented as [[IBM PC AT 5170 Technical Reference (September 1985)]]; the March 1984 edition is also hosted. Section 1 "System Board" for the feature list, the eight I/O slots (six with a 36-pin and a 62-pin socket, two with only the 62-pin socket) and the type 1 and type 2 memory arrangements; Section 1 "Specifications" for the 540 &times; 439 &times; 162 mm size and the 20.0 kg weight; Section 3 "Power Supply", pages 3-3 to 3-7, for the input requirements, the dc load currents and regulation tolerances, the 20 ms output protection, output voltage sequencing, no-load operation, the 'power-good' signal and its one-second off requirement, and the 5 ohm 50 W load resistor on P10.</ref> minuszerodegrees describes the type 1 board as two banks of 256 KB, counting the piggybacked 41128 pairs as single positions; the two descriptions are of the same board.<ref name="mzat" />

A type 1 board can run with only bank 0 populated. Switching between single-bank and dual-bank operation needs the BIOS reconfigured through SETUP and may need '''jumper J18''' moved.<ref name="mzat" />

The memory module sockets on system boards P/N 8286112, P/N 6480170 and P/N 6480072 were redesigned: the contact surface sits below the top of the pin holes and is not visible from above. It is functionally equivalent to the old style, and a board that looks like it has no contacts is not faulty.<ref name="fsim" />

== BIOS Revisions ==

The BIOS, including [[IBM Cassette BASIC|cassette BASIC]], is 64 KB. Very early boards carry four 16 KB 27128 devices at U17/U27/U37/U47; later production uses two 32 KB 27256 devices at U27 and U47. On type 1 boards, shunt block '''U131''' selects which ROM type is fitted.<ref name="mzat" />

{| class="wikitable styled-table" style="width:95%;"
|+'''IBM 5170 BIOS revisions'''
! Date !! Mask ROM !! EPROM !! 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 01/10/84 to 06/10/85 upgrade: the 30 MB hard drive upgrade kit for type 1 machines included 06/10/85 ROMs, because the 30 MB drive needed the newer code. Whether IBM ever endorsed an upgrade to 11/15/85 is not known; it is desirable because it adds 1.44 MB diskette support, and owners who have tried it on 6 MHz boards report no problems, but it was designed for an 8 MHz board.<ref name="mzat" />

=== The 601 that is not a fault ===

With the '''06/10/85''' and '''11/15/85''' BIOS, removing the IBM Fixed Disk and Diskette Drive Adapter and fitting a third-party replacement can produce a '''601''' at POST. Those revisions expect that adapter, or something that identifies itself the same way; the 601 is the POST telling you it did not find one. It does not stop the boot &mdash; a prompt to press F1 follows &mdash; although diskette operation may be compromised. The 01/10/84 BIOS does not do this. Fitting a card that behaves like IBM's, such as a Western Digital WD1003A-WA2, avoids it.<ref name="mzat" />

== Expansion ==

'''Eight I/O slots, but they are not all the same.''' IBM's ''Technical Reference'' specifies "six with a 36-pin and a 62-pin card-edge socket, two with only the 62-pin card-edge socket" &mdash; so '''six 16-bit slots and two 8-bit slots'''.<ref name="trat" /> An 8-bit card fits either kind; a 16-bit card needs one of the six.

== Storage ==

* '''Diskette''' &mdash; a 1.2 MB high-capacity 5.25-inch drive. The 1.2 MB drive's head is half the track width of a 360 KB drive's, so a 360 KB diskette written in a 1.2 MB drive is often unreadable in a real 360 KB drive afterwards. The drive cannot detect media type; the user has to use the right media.
* '''Fixed disk''' &mdash; an optional 20 MB or 30 MB drive on the '''IBM Fixed Disk and Diskette Drive Adapter''', the 16-bit "combo" card that carries both controllers.<ref name="fsim" />
* '''Keylock''' &mdash; a keyed front-panel lock disables the keyboard and holds the cover on. If the key is lost, the cover can still be removed: with the unit flat on the bench and the five rear cover screws out, insert a screwdriver into the gap between frame and cover from underneath, in line with the lock, and lift &mdash; this raises the cover lip over the latch. To run diagnostics in that state, remove one wire from the lock switch to re-enable the keyboard.<ref name="fsim" />

== Display and Ports ==

There is no video on the system board; MDA, CGA, EGA and PGA cards were all used.

'''There is no serial or parallel port on the system board either.''' Both are on the separate '''IBM PC AT Serial/Parallel Adapter''', whose serial side is built around an NS16450 UART &mdash; a single-byte-buffer part like the 8250 in the [[IBM PC (5150)|5150]], and the reason high-speed serial work on an AT wants a 16550-class replacement.<ref name="trat" />

== Keyboard ==

The AT introduced the '''84-key AT keyboard''', with the numeric keypad separated from the main group and three lock lamps. The connector is the same DIN-5 as the XT's, but the interface is '''bidirectional''' and the scan code set is different, so an XT keyboard will not work on an AT and an AT keyboard will not work on a [[IBM PC (5150)|5150]] or [[IBM PC XT (5160)|5160]] without a converter.<ref name="mzkbd">[https://www.minuszerodegrees.net/5150/keyboard/5150_keyboard_support.htm IBM 5150 &mdash; Keyboards], minuszerodegrees.net. Source for IBM's own name for this keyboard ("83-key keyboard"), the type 1 / type 2 distinction in reset behaviour, the point that "Model F" is a family name covering keyboards that will not work with a 5150, the reassembly warning, the cable metering diagram, and the incompatibility of AT-protocol keyboards.</ref> From the type 3 board era the AT shipped with the 101-key Enhanced Keyboard instead.

== Power Supply ==

Approximately '''192 W'''.<ref name="mzat" /> IBM's own figures:<ref name="trat" /><ref name="fsim" />

{| class="wikitable styled-table" style="width:90%; text-align:center;"
|+'''IBM 5170 &mdash; dc load requirements and sense levels'''
! Rail !! Minimum load !! Maximum load !! Regulation !! Minimum sense level
|-
| +5 Vdc || 7.0 A || 19.8 A || +5% to &minus;4% || +4.5 V
|-
| &minus;5 Vdc || 0.0 A || 0.3 A || +10% to &minus;8% || &minus;4.3 V
|-
| +12 Vdc || 2.5 A || 7.3 A || +5% to &minus;4% || +10.8 V
|-
| &minus;12 Vdc || 0.0 A || 0.3 A || +10% to &minus;9% || &minus;10.2 V
|}

The supply also provides switched '''115 Vac or 230 Vac for the IBM Monochrome Display'''.<ref name="trat" /> Input is 100&ndash;125 Vac at up to 5 A, or 200&ndash;240 Vac at up to 3 A, selected by a switch above the power-cord socket; maximum in-rush current is 100 A.<ref name="trat" /><ref name="fsim" /> Heat output is 1100 BTU/hr.<ref name="fsim" />

Protection and behaviour:<ref name="trat" />

* If any output becomes overloaded the supply '''switches off within 20 ms'''. An over-current condition does not damage it.
* Output voltages track within 300 ms of each other at power-on and power-off, provided minimum loading is present.
* No damage occurs with no load, but the supply may switch off and need a power-on reset.
* '''Switch off for at least one second''' before switching on again, or 'power good' will not be generated. It has a turn-on delay of at least 100 ms and no more than 500 ms, and can drive six standard TTL loads.

=== The load resistor ===

The +12 V rail needs '''2.5 A minimum'''. An AT system board provides very little +12 V load on its own, so machines shipped without a fixed disk carry a '''5 ohm, 50 watt resistor''' on P10 in its place.<ref name="trat" /> At 12 V that draws about 2.4 A &mdash; roughly 29 W &mdash; and it gets hot in normal operation. That heat is not a fault.<ref name="mzat" />

=== A supply fault that only appears when warm ===

IBM's own service tip: some 5170 power supplies fail after two or more hours powered on, then work correctly again once the machine has been switched off and has cooled. IBM's instruction in that case is to replace the supply.<ref name="fsim" />

== The Battery and the 161 Error ==

The AT keeps its configuration in battery-backed CMOS alongside a Motorola MC146818 real-time clock. IBM's procedure for checking the battery:<ref name="fsim" />

# Switch the system unit off and remove the cover.
# '''Disconnect the battery from the system board.''' Measuring it while connected gives varying readings because of the board's drain.
# Meter on the 12 V dc range, common lead to pin 1 and voltage lead to pin 4 of the battery connector.
# Look for '''6.0 Vdc minimum'''.

A '''161''' ("battery defective or new battery installed") appears on the first POST after any battery change. If you have just fitted a new one, that is expected &mdash; run SETUP.<ref name="fsim" />

== Diagnosing Memory Errors ==

IBM's memory error reporting on the AT is more informative than it looks:<ref name="fsim" />

* '''Parity check 1''' &mdash; a system board parity error. '''Parity check 2''' &mdash; a Memory Expansion Adapter parity error.
* A '''10-character error code''' beginning 00, 01, 02, 03, 04, 05, 06 or 07 is a system board memory failure. The first two characters give the bank &mdash; '''00 to 03 is bank 0, 04 to 07 is bank 1''' &mdash; and the last four characters identify the failing module within it. For example, 04002 8000 points at a specific chip in bank 1.
* If the first character of a parity check error is 8 or 9, replace the 18 memory modules of the base Memory Expansion Adapter; if the same code returns, replace the adapter.
* If a diagnostic passes on bare system-board memory, refit Memory Expansion Adapters one at a time, running SETUP each time so the memory size is right.

'''Models 068 and 099''' with system board P/N 8286112, an Enhanced Graphics Adapter and the 0.5 MB to 2 MB Memory Expansion Adapter produce a spurious '''Parity Check 2''' message after a soft boot (Ctrl-Alt-Del). IBM's fix is '''ECA024''', not a memory replacement.<ref name="fsim" />

== Blank Display, No Beep &mdash; Check the Coprocessor First ==

Some 5170 planars left the factory with the '''math coprocessor socket fitted the wrong way round''', notch to the rear of the board. An 80287 installed to match the socket notch then fails power-on diagnostics: blank display, no beep. '''Installing the coprocessor with its notch towards the front of the planar corrects it.'''<ref name="fsim" /> It is worth checking before condemning a board, and it is worth remembering when moving a coprocessor to a replacement board &mdash; IBM's own manual reminds engineers not to forget to transfer it.<ref name="fsim" />

== General Maintenance ==

Rail checks, battery replacement, cleaning and slot care are in [[IBM PC AT Maintenance Guide]].

== Troubleshooting ==

Beep codes, 1xx system board errors, the 161/162/163 cluster, the 601 combo-card message, CMI hard drive symptoms and other AT-specific problems are in [[IBM PC AT Troubleshooting Guide]].

== Capacitor Replacement ==

Tantalum work on the system board and the switching supply is in [[IBM PC AT Capacitor Replacement Guide]].

== Gallery ==
<gallery mode="packed" heights="200">
File:IBM PC AT 5170.jpg|IBM Personal Computer AT (5170)
File:IBM 5170 front.jpg|Front view
File:IBM 5170 back.jpg|Rear view
File:IBM 5170 motherboard Type 2.jpg|Type 2 system board
</gallery>

== References ==

<references />

== Related Pages ==

* [[IBM PC AT Maintenance Guide]] &middot; [[IBM PC AT Troubleshooting Guide]] &middot; [[IBM PC AT Capacitor Replacement Guide]]
* [[IBM PC (5150)]] &middot; [[IBM PC XT (5160)]]
* [[IBM Monochrome Display Adapter]] &middot; [[IBM Color Graphics Adapter]] &middot; [[IBM 5151]] &middot; [[IBM 5153]]
* [[IBM PC AT 5170 Technical Reference (September 1985)]] &middot; [[IBM Personal Computer Family Service Information Manual]] &mdash; IBM's own references, hosted here

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[[Category:IBM]]