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Rewrite from SM SY34-0171-0 and DUG 6841631: IBM forbids cleaning the head/carriage (p. 5-3), supply is ferroresonant or TSR (p. 2-57), taps are on T1/TB; remove uncited chip, ROS, RAM, ATX and brush-motor claims; add covers, jumpers, storage table, tap charts, IBM tool list
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[[File:IBM System 23 Datamaster front.jpg|thumb|320px|IBM System/23 Datamaster (5322). The power supply slides out of the rear into a defined service position, with the fuses and voltage test points accessible. (Image: Wikimedia Commons)]]
<templatestyles src="Template:StyledTable/styles.css" />
This guide documents preventive maintenance for the '''[[IBM System/23 Datamaster]]''' (Model 5322 all-in-one desktop and Model 5324 tower variant), announced by IBM on 28 July 1981. The Datamaster's hardware is the direct architectural ancestor of the [[IBM PC (5150)]] and uses the same 9-bit parity DRAM, 62-pin expansion bus (with only 5 signals changed), 8253 PIT, 8259 PIC, capacitive Model F keyboard mechanism and Power Good signal. Restoration of a Datamaster is therefore closely related to PC-era practice — with two large exceptions: the 8-inch diskette drives belong to the older [[IBM 5120|5120]] generation, and '''the power supply is ferroresonant''', which is a different animal from either a linear supply or a PC switcher.
[[File:IBM System 23 Datamaster front.jpg|thumb|320px|IBM System/23 Datamaster 5322]]
 
This guide covers maintenance of the '''[[IBM System/23 Datamaster]]''' 5322, the one-piece desk-top unit with a built-in display, keyboard and up to two 8-inch diskette drives. It follows IBM's [[IBM 5322 Computer Service Manual|5322 Computer Service Manual]] (SY34-0171-0) and [[IBM System 23 Diagnostic User Guide|Diagnostic User Guide]] (PN 6841631). The floor-standing 5324 has its own service manual (SY34-0241-1), which is on bitsavers.<ref name="bs">bitsavers, [http://bitsavers.org/pdf/ibm/system23/fe/ ibm/system23/fe] (retrieved 2026-09-30): SY34-0171-0 5322 Computer Service Manual, SY34-0241-1 5324 Computer Service Manual (May 1982), Diagnostic User Guide 6841631 (August 1981 and April 1982 editions), 5324 MAPs; and [http://bitsavers.org/pdf/ibm/system23/5247/ ibm/system23/5247]: SY34-0243-0 5247 Disk Unit Service Manual (April 1982).</ref>
== Safety ==
 
'''The 5322's supply is ferroresonant, and IBM prints its own DANGER notice about it:'''


: "'''Up to 800 Vac is generated in the power supply.''' Before removing the power supply or any power supply part, switch off the 5322 power and disconnect the power cable from the ac service outlet."<ref name="sm5322">IBM, ''IBM 5322 Computer Service Manual'', SY34-0171-0, December 1980 &mdash; hosted on this wiki as [[IBM 5322 Computer Service Manual]]. Chapter 2: items 1200 (locations), 1210 (AC voltage distribution for supplies PN 6838279, 6838280 and 6838281, with the mains-tap jumper tables), 1211 (DC voltage distribution, IBM's voltage tolerance and peak-to-peak ripple table, and the meter-and-capacitor ripple measurement method), 1212 (signal cable pin assignments), 1230 (CPU planar board and connector pin assignments), 1240/1250/1260 (power supply layout, showing resonant capacitor C6, terminal block TB1, the power-good LED and AC input fuse F6, with the "Up to 800 Vac is generated in the power supply" DANGER notice), 1241/1251/1261 (the F1 to F5 rail fuses and ratings) and 1270 (cooling fan). Theory of operation: the 5322 model numbering, the 305 mm (12 in.) CRT showing 24 lines of 80 characters, the 83-key keyboard, the brightness-control warning, and the standard and optional features. Chapter 5: items 1550 (AC drive motor) and 1551 (the drive motor run capacitor, with its own DANGER notice and discharge instruction).</ref>
== ⚠️ Safety ==


That is eight hundred volts AC, generated inside a box that looks like an ordinary transformer supply. The layout names a '''resonant capacitor C6''' and a tapped transformer with jumper-selected mains taps on terminal block TB1.<ref name="sm5322" /> Descriptions of this supply as a bridge-and-series-pass-regulator linear design &mdash; including the one that used to be on this page &mdash; are wrong, and the difference is not academic.
'''IBM's DANGER notice: up to 800 V AC is generated in the power supply.''' Before removing the supply or any part of it, switch off the 5322 and disconnect the power cable from the outlet.<ref name="sm221">IBM, ''IBM 5322 Computer Service Manual'', SY34-0171-0 (December 1980), item 1240, p. 2-21, power supply removal and replacement ([[IBM 5322 Computer Service Manual|hosted here]]).</ref>


# Power off and '''unplug at the wall'''.
# Switch off and unplug the 5322 before removing any cover.
# Discharge through a resistor and verify with a meter before touching anything.
# The power supply slides out of the rear into a service position. To switch on with the supply in that position, IBM first has the engineer check grounding continuity between the 5322 main base plate and the power supply frame with the meter on the ohms RX1 range.<ref name="sm221" />
# The supply has a '''service position''': it slides out of the rear of the machine with two screws removed, and in that position the fuses, voltage test points and power switch are all accessible without disconnecting anything. If you intend to switch the machine on with the supply in the service position, IBM says to '''first confirm grounding continuity between the 5322 base plate and the power supply frame''' with a meter on the ohms range.<ref name="sm5322" />
# Follow the [[CRT Discharge Procedure]] before working near the display unit.
# For the CRT, follow the [[CRT Discharge Procedure]] and discharge a second time a few minutes later.
# Each diskette drive has an AC drive motor with a capacitor. IBM warns that high voltage may be present at the capacitor terminals and discharges it by shorting the terminals with an insulated screwdriver before disconnecting the motor leads.<ref name="sm540">IBM 5322 Computer Service Manual, SY34-0171-0, item 1551, p. 5-40.</ref>
# '''The diskette drives have their own hazard.''' Each drive has an AC drive motor with a mains-rated run capacitor, and IBM's warning is "High voltage may be present at the capacitor terminals." Its procedure is to remove the insulator caps and '''discharge the capacitor by shorting its terminals with an insulated screwdriver''' before disconnecting the motor leads.<ref name="sm5322" />


See also [[Recommended Tools]] and [[Battery Explosion, Capacitor or Corrosion Damage]].
See also [[Recommended Tools]] and [[Battery Explosion, Capacitor or Corrosion Damage]].


== Documentation Set ==
== Documentation ==


The complete IBM service documentation set for the System/23 is preserved at [http://bitsavers.org/pdf/ibm/system23/ Bitsavers]:
* [[IBM 5322 Computer Service Manual]], SY34-0171-0 (December 1980): locations, removal and adjustment procedures, theory of operation and parts catalogue for the 5322, its power supplies, keyboard, display and internal diskette drives. Hosted here.
* [[IBM System 23 Diagnostic User Guide]], PN 6841631 (April 1982): the power-on test (PID 1200), the ROS-resident diskette test (PID 1500) and the diskette-resident diagnostic and utility programs. Hosted here.
* On bitsavers: the 5324 Computer Service Manual (SY34-0241-1, May 1982), the 5324 maintenance analysis procedures, the August 1981 edition of the Diagnostic User Guide and the 5247 Disk Unit Service Manual (SY34-0243-0).<ref name="bs" />


* '''SY34-0171-0''' — IBM 5322 Computer Service Manual, December 1980. The primary CE document; covers diagnostics, power supply, drives, board layouts, schematics. Indispensable for any Datamaster restoration.
IBM's own tool list for the System/23 is the CE meter (PN 1749231), the GLP II logic probe (453212), the metric tool kit (1749235), a plastic CRT adjustment screwdriver (460811), and at branch level a ROS module puller (1715889), a module pin aligning tool (453473), a ground check tool (9900453) and a Tektronix 465 or equivalent oscilloscope.<ref name="dug17">IBM, ''Diagnostic User Guide 0001, System/23 with Diskette'', PN 6841631, EC 327594 (April 1982), section 11, pp. 17-18 ([[IBM System 23 Diagnostic User Guide|hosted here]]).</ref> The ripple check below also needs a 0.22 µF, 50 V capacitor.
* '''SY34-0241-1''' — IBM 5324 Computer Service Manual, May 1982.
* '''6841631''' — System/23 Diagnostic User Guide, April 1982 (complete PID-1200 test ID list).
* '''SA34-0107-3''' — System/23 Setup Instructions (5322), June 1982.
* '''ZA38-0016-0''' — Commonly Used Systems Parts Handbook, July 1988 (p. 119 lists 5322 / 5324 motherboard parts).


Download all of these for any serious Datamaster work.
== Opening the 5322 ==


== Opening the System Unit ==
IBM's cover procedures (item 1220):<ref name="sm214">IBM 5322 Computer Service Manual, SY34-0171-0, item 1220, p. 2-14, covers.</ref>


Tools: Philips #2 screwdriver, T15 / T20 Torx, anti-static strap, high-voltage probe.
* Rear access cover: pull it toward the rear until the pressure latches release.
* Top cover: remove the rear access cover and two screws, then pull the top cover toward the rear to free the front locating tabs.
* Keyboard cover: remove two screws, lift the front edge and pull it forward.
* Front cover: remove the rear access, top and keyboard covers and the keyboard (item 1330), put the power supply and planar board in their service positions, pull off the brightness knob (it is keyed to its shaft), turn the diskette latches horizontal, then remove five screws from the main support plate and centre bracket and 11 screws from the bottom cover.


A distinctive feature of the 5322 chassis: '''both the power supply and the motherboard slide out from the rear''' without removing the main cover. This is unusual for the era and means most service operations can be performed without disturbing the integrated CRT cradle.
=== CPU planar board drawer ===


# Power off and unplug all cables (mains, keyboard, printer, communications, external diskette unit cable).
The CPU planar board sits in a drawer at the rear. Remove the rear access cover, take the I/O cables out of the ground clamp, remove the two screws at the rear of the drawer and slide it out to its service position. In that position the attachment cards, cables, CE test pins and feature jumper pins are accessible. When a planar board is replaced, move each feature jumper to the same position on the new board, and afterwards check the display's horizontal centering adjustment (item 1440).<ref name="sm216">IBM 5322 Computer Service Manual, SY34-0171-0, item 1230, pp. 2-16 and 2-17, CPU planar board removal, replacement and diagram.</ref>
# Rear cover plate — held by Philips screws around the perimeter.
# '''Motherboard sled''' — slides out horizontally from the rear once retaining screws are removed.
# '''PSU sled''' — slides out similarly from a separate rear bay.
# The integrated 12-inch CRT and its deflection sub-chassis remain in the main chassis.
# Drive cage — accessed by removing the front bezel and lifting the drive sled.


=== The CRT is 12 inches, and that is now settled ===
=== Power supply ===


'''IBM's own service manual states it: "The CRT display unit has a 305 mm (12 in.) video screen."'''<ref name="sm5322" /> It displays 24 lines of 80 characters, 1,920 characters in total. This page previously hedged between 9 and 12 inches because no primary source had been checked; the manual is now hosted here and the question is closed.
Remove the rear access cover and top cover, open the ground clamp and take out the I/O cables, remove the two screws at the rear of the supply and slide it out. The fuses, voltage test points and power switch can be reached in this service position. To remove the supply completely, unplug P1 to P5 and the diskette attachment cable voltage wires, and replace any cable ties that had to be cut.<ref name="sm221" />


One operating note from the same manual that is worth passing on to owners: '''do not run the machine with the brightness control fully clockwise for long periods''' &mdash; IBM says the display screen can be damaged.<ref name="sm5322" />
== Planar board jumpers and storage ==


== Detached Keyboard ==
The CPU planar diagram shows these jumper positions:<ref name="sm216" />


The 5322's keyboard is a '''separate unit''' connecting to the system via a multi-pin cable:
* A1: CE loop on test. A2: CE stop on error. A3: machine update card installed.
* B1 to B5: country select. C2: internal diskette not installed. A separate jumper is fitted on 50 Hz machines only.
* IBM warns that other jumper pins on the planar are for manufacturing use and are not jumpered in normal operation.


* '''83-key capacitive Model F''' (or rather, the pre-Model F mechanism — the Datamaster keyboard is often cited as the earliest production version of the design).
Read/write storage is on one or two cards in the base and feature sockets. The base socket is always used.<ref name="sm216" />
* '''Intel 8048''' microcontroller inside the keyboard with '''Datamaster-specific firmware'''. '''Critical''': the 8048's firmware is unique to the Datamaster — '''IBM PC keyboard 8048 firmware is not interchangeable'''. A failed 8048 means the keyboard cannot be made to work with another Datamaster unless you have a donor keyboard.
* Interface to the motherboard is '''parallel''' (driven by an 8255 PPI port). The IBM PC moved the same keyboard mechanism to a serial interface.


== Inspecting the Chassis ==
{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+'''5322 storage cards and 64K card jumpers (SM p. 2-17)'''
! Total storage !! Feature socket !! Base socket !! 64K card jumpers
|-
| 32K || - || 32K || -
|-
| 64K || 32K || 32K || -
|-
| 64K || - || 64K || 1 and 3
|-
| 96K || 32K || 64K || 2 and 4
|-
| 128K || 64K || 64K || 2 and 4
|}


Inspection items (in order):
The power-on test checks storage in 16K blocks as routines 2A to 30. Routines 2A, 2D and 2E cover the base socket and 2B, 2C, 2F and 30 the feature socket.<ref name="dug79">IBM, ''Diagnostic User Guide 0001'', PN 6841631, section 21.4.1.11, p. 79.</ref>


# '''PSU bulk filter capacitors''' — visual check for bulging tops, leaked electrolyte, discolouration. Linear PSU caps at 40+ years old are the highest-likelihood failure point.
== Power supply checks ==
# '''Series-pass regulator transistors''' — heatsink-mounted; check thermal paste; replace if dried out.
# '''Memory daughter card decoupling caps''' — community references specifically flag these as failure points. '''A shorted decoupling cap on the RAM rails will brick the system'''; recommended triage is to '''remove the bypass caps as a first test''' before suspecting the RAM itself.
# '''Flyback / deflection board''' — inspect for cracked solder joints.
# '''Phosphor''' — check for burn-in.
# '''8-inch floppy drive belts''' — perished urethane is the dominant failure on these drives.
# '''Spindle motor brushes''' — wear is common after 40+ years.
# '''Mostek MK36000 ROS modules''' — visually inspect for moisture damage / bulging package. These ROMs are a documented Datamaster failure mode.
# '''Keyboard 8048''' — confirm operational before any other keyboard work.


== Regular Cleaning ==
A 5322 has either a ferroresonant supply or a transistor-switching-regulator (TSR) supply; IBM describes them as functionally interchangeable. Both give -5, +5, -12, +12 and +24 V DC and 120 V AC for the diskette motors, display and fan. The power-good LED, visible from the rear of the supply, is lit when -5, +5, -12 and +12 V are within about 80 % of nominal.<ref name="sm257">IBM 5322 Computer Service Manual, SY34-0171-0, p. 2-57, "Power supplies".</ref>


* Soft brush and low-pressure compressed air for the motherboard, ROS sockets, RAM daughter cards, drive bays, and PSU vents.
Measure at the power supply A1 card, where IBM's tolerances apply:<ref name="sm211">IBM 5322 Computer Service Manual, SY34-0171-0, item 1211, p. 2-11, DC voltage distribution diagram.</ref>
* '''Do not''' use compressed air over a leaking electrolytic — it spreads electrolyte across the board.
* Detach the keyboard for separate cleaning; wipe with slightly damp microfibre.
* Remove keycaps using the IBM tool (the Datamaster uses the same capacitive-Model-F mechanism that became the IBM PC AT / Model F keyboard).
* Clean 8-inch floppy heads with isopropyl alcohol on a '''foam swab''' (not cotton — cotton fibres in the head gap cause CRC errors).
* Inspect every diskette before reading. Old IBM 8-inch media may have lost binder integrity; if oxide is shedding, do not load.


== Expected Measurements ==
{| class="wikitable styled-table" style="width:80%; text-align:center;"
 
|+'''IBM 5322 DC outputs: tolerance, ripple limit and fuse'''
'''Measure at the power supply A1 card.''' IBM says explicitly that its tolerances apply there and not elsewhere.<ref name="sm5322" />
! Output !! Tolerance !! Ripple, peak to peak !! Fuse
 
<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:95%;"
|+'''IBM 5322 — IBM's own voltage tolerances and ripple limits'''
! Voltage !! Tolerance !! Peak-to-peak ripple limit !! Fuse
|-
|-
| '''+5 Vdc''' || +4.6 to +5.5 V || 0.12 V || '''F5''', 10 A
| +5 V || +4.6 to +5.5 V || 0.12 V || F5, 10 A
|-
|-
| '''&minus;5 Vdc''' || &minus;4.6 to &minus;5.5 V || 0.05 V || '''F1''', 0.5 A
| -5 V || -4.6 to -5.5 V || 0.05 V || F1, 0.5 A
|-
|-
| '''+12 Vdc''' || +11.0 to +13.2 V || 0.175 V || '''F2''', 1.5 A
| +12 V || +11.0 to +13.2 V || 0.175 V || F2, 1.5 A
|-
|-
| '''&minus;12 Vdc''' || &minus;11.0 to &minus;13.2 V || 0.12 V || '''F3''', 0.5 A
| -12 V || -11.0 to -13.2 V || 0.12 V || F3, 0.5 A
|-
|-
| '''+24 Vdc''' || +22.0 to +26.4 V || 0.325 V || '''F4''', 1.5 A
| +24 V || +22.0 to +26.4 V || 0.325 V || F4, 1.5 A
|-
|-
| '''Power good''' || +2.4 to +5.5 V || 0 || &mdash;
| Power good || +2.4 to +5.5 V || 0 || -
|}
|}


'''The symmetrical ±5 % table previously on this page was not IBM's''' and was wrong in both directions — it called a perfectly healthy &minus;12.8 V rail a fault and would have passed a +24 V rail at +25.2 V that IBM allows up to +26.4 V.
To check ripple without an oscilloscope, put a capacitor of 0.22 µF or more (50 V DC or higher) in series with one lead of the meter, set the 2.5 V AC range, and connect between the output and frame ground. If the pointer moves off zero, excess ripple may be present.<ref name="sm211" />


'''There is a power-good LED on the supply itself''', so the simplest possible first check needs no instrument at all.<ref name="sm5322" />
The five fuse ratings are the same on all three documented supplies. IBM checks a fuse for continuity on the ohms RX1 range and warns never to fit one of a higher rating.<ref name="smfuse">IBM 5322 Computer Service Manual, SY34-0171-0, items 1241 (p. 2-22), 1251 (p. 2-29) and 1261 (p. 2-35).</ref> The US and Canada supply has AC input fuse F6, 5 A slow-blow;<ref name="sm223">IBM 5322 Computer Service Manual, SY34-0171-0, item 1241, p. 2-23.</ref> the GBG/I supplies have circuit breaker CB1 instead.<ref name="sm257" />


=== Measuring ripple without a scope ===
=== Mains voltage taps ===


IBM publishes a method for exactly this, and it is the most useful thing in the chapter:<ref name="sm5322" />
The three documented supplies are PN 6838279 (60 Hz, Canada and US), PN 6838280 (60 Hz, GBG/I) and PN 6838281 (50 Hz, GBG/I). The two GBG/I supplies are set for the local mains by the line connection and jumpers on the transformer terminal board T1/TB; IBM's diagrams show both wired for 220 V. To change the setting, measure the outlet voltage, put the supply in the service position and rewire T1/TB from the chart. For a supply with a different part number, IBM says to follow the labels on the supply.<ref name="sm209">IBM 5322 Computer Service Manual, SY34-0171-0, item 1210, pp. 2-9 and 2-10 (AC voltage charts), and items 1250 and 1260, pp. 2-28 and 2-34 (AC line voltage selection).</ref>


# Connect a capacitor, '''0.22 µF or larger, rated 50 Vdc or higher''', in series with one meter lead. (IBM notes the capacitor is not supplied with the meter.)
{| class="wikitable styled-table" style="width:90%; text-align:center;"
# Set the meter range to '''2.5 Vac'''.
|+'''T1/TB settings, GBG/I supplies (SM pp. 2-9, 2-10)'''
# Connect one lead to the DC voltage in question and the other to frame ground, remembering the capacitor is in series.
! Mains !! PN 6838280 (60 Hz) line !! PN 6838280 jumpers !! PN 6838281 (50 Hz) line !! PN 6838281 jumpers
# '''If the pointer leaves zero, excess ripple may be present.'''
|-
| 100 V || 1-7 || 1-6, 2-7, 4-9 || 1-6 || 1-5, 2-6, 4-8
|-
| 110 V || 1-8 || 1-6, 3-8, 4-9 || 1-7 || 1-5, 3-7, 4-8
|-
| 120 V || 1-9 || 1-6, 4-9 || - || -
|-
| 127 V || 1-10 || 1-6, 5-10, 4-9 || - || -
|-
| 200/208 V || 1-7 || 2-6 || 1-6 (200 V) || 2-5
|-
| 220 V || 1-8 || 3-6 || 1-7 || 3-5
|-
| 230 V || - || - || 1-8 || 3-5
|-
| 240 V || 1-9 || 4-6 || 1-8 || 4-5
|}


Compare against the peak-to-peak limits in the table above. Ripple is the measurement that actually finds a tired supply; a rail can sit dead centre of its voltage band and still be unusable.
== Display ==


=== The fuses tell you where the fault is ===
The CRT display unit has a 305 mm (12 in.) screen showing 24 lines of 80 characters. IBM warns against running the 5322 with the brightness control fully clockwise for long periods, because the screen could be damaged.<ref name="sm241">IBM 5322 Computer Service Manual, SY34-0171-0, pp. 2-41 (standard features) and 2-43 (operator controls).</ref>


Every DC output has its own fuse, which makes diagnosis unusually clean:<ref name="sm5322" />
== Diskette drives ==


* '''F5 blown (10 A, +5 V)''' — something is shorting the main logic rail.
The internal drives are the 31SD (one read/write head) and the 51TD (two heads); they differ only in the head/carriage assembly and the drive control card. IBM's maintenance preface says:<ref name="sm53">IBM 5322 Computer Service Manual, SY34-0171-0, p. 5-3, maintenance preface.</ref>
* '''F4 blown (1.5 A, +24 V)''' — the diskette side: a spindle motor, a head load, or the drive cable.
* '''F2 or F3 (1.5 A / 0.5 A, ±12 V)''' — serial interface and drive logic.
* '''F1 (0.5 A, &minus;5 V)''' — bias.
* '''F6''' is the AC input fuse.


IBM's own check is continuity on the ohms RX1 range, using a fuse puller to remove them. '''Never replace a fuse with one of a higher rating''' — IBM's warning, and on a supply that generates 800 Vac internally it is worth taking literally.<ref name="sm5322" />
* There is no preventive maintenance for the diskette drive. Repairs are adjustments and FRU replacements directed by the MAPs, verified with the diagnostics.
* The head/carriage assembly can be replaced in the field, but "do not repair or clean any part of this assembly".
* The drive hub and pulley assembly is adjusted at the factory and is not field-replaceable; if it or the track 40 adjustment surface is damaged, replace the whole drive.
* Keep television sets, display terminals and other electromagnetic devices at least 0.61 m (2 ft) from the 5322.


=== Three supplies, three mains-tap tables ===
The drive motor turns the hub through a belt (item 1552). When refitting the motor fan and pulley, IBM sets a 0.5 mm (0.020 in.) gap between the motor and the fan hub, with the setscrew on the flat of the shaft, and fits the fan enclosure so the belt sits in its recess.<ref name="sm541">IBM 5322 Computer Service Manual, SY34-0171-0, item 1552, p. 5-41.</ref>


'''PN 6838279''' is the 60 Hz Canada and US supply. '''PN 6838280''' is 60 Hz General Business Group/International and '''PN 6838281''' is 50 Hz GBG/I; both of those select the mains voltage by jumpers on terminal block TB1, covering 100, 110, 120, 127, 200/208, 220, 230 and 240 V — '''and the two tables are not the same'''.<ref name="sm5322" /> Check which supply you have and which taps are fitted before switching on an imported machine. IBM also notes that if the supply in a given 5322 carries a different part number, the labels on that supply govern, not the manual's diagrams.
On the 31SD, the head load arm carries a pressure pad. IBM replaces it when it has worn level with the arm, using kit 2200751 (which includes pad tool 2200750). Old adhesive is cleaned off the arm's mounting surface with tissue moistened with isopropyl alcohol; the head itself is not cleaned. IBM warns not to touch the pad surface or let the arm hit the read/write head.<ref name="sm529">IBM 5322 Computer Service Manual, SY34-0171-0, item 1531, p. 5-29.</ref>


== ATX PSU Substitution (Bench-Test) ==
Diskettes should be kept at 10 to 51 °C and 8 to 80 % relative humidity, stored flat in their envelopes in stacks of up to ten, and kept away from heat and sunlight.<ref name="sm563">IBM 5322 Computer Service Manual, SY34-0171-0, pp. 5-62 and 5-63, diskette handling.</ref>


It is documented community practice to '''substitute a modern ATX PSU as a bench-test power source''' once the original Molex pinout is matched.<ref name="bp">Bits Passats, "IBM System/23 Datamaster". A community restoration write-up built from a working machine; the source for the shorted decoupling capacitor triage on the memory daughter cards and for the bench-supply substitution practice. Community source, not an IBM document.</ref> The +24 V rail must be supplied separately (an ATX supply does not include +24 V); restorers commonly use a small standalone +24 V brick for floppy spindle power.
== Keyboard ==


This is suitable for board-level diagnostics but is '''not''' a permanent replacement — the integrated CRT deflection board requires the original PSU's +12 V and high-voltage primary feed.
The keyboard has 83 keys over a capacitive matrix, scanned by a microprocessor on the keyboard card, which sends a scan code and an interrupt request to the processing unit. The complete keyboard assembly is one field-replaceable unit.<ref name="sm316">IBM 5322 Computer Service Manual, SY34-0171-0, p. 3-16, keyboard data flow.</ref> At power-on, routine 35 resets the keyboard; its processor runs its own test and replies X'2A55', or X'552A' if the test failed.<ref name="dug80">IBM, ''Diagnostic User Guide 0001'', PN 6841631, section 21.4.1.16, p. 80.</ref>


== 8-Inch Floppy Drive Maintenance ==
== Related pages ==


The 5322 has 0, 1 or 2 × built-in 8-inch floppy drives (typically Shugart-class in IBM cosmetics). Maintenance:
* [[IBM System/23 Datamaster]], [[IBM System/23 Datamaster Troubleshooting Guide]], [[IBM System/23 Datamaster Capacitor Replacement Guide]]
 
* [[IBM 5322 Computer Service Manual]] and [[IBM System 23 Diagnostic User Guide]], both hosted here
* '''Drive belt''' — perished urethane. Modern replacements available from the 8-inch floppy restoration community.
* [[IBM 5120 Maintenance Guide]]
* '''Head load solenoid''' — exercise; replace if fatigued.
* [[Floppy Drive Repair]]
* '''Spindle motor''' — brush wear is the main failure. Brushes can be re-sourced from industrial motor suppliers.
* '''Read / write head''' — clean with IPA on a foam swab.
* '''Head alignment''' — verify against a known-good diskette using the procedure in SY34-0171-0.
* '''Oxide shedding''' from old IBM media — inspect every diskette before loading. Do not load shedding diskettes.
 
== Optional External Storage ==
 
* '''IBM 5246 Diskette Unit''' — external 1 or 2 × 8-inch floppy drive enclosure. Service procedures match the internal drives.
* '''IBM 5247 Winchester Disk Unit''' — 15.4 MB or 30.8 MB 8-inch hard drive. Has its own linear PSU and disk controller card. If the 5247 is shared between multiple Datamaster hosts, verify the host-selection cabling per the 5247 manual before any service work.
 
== ROS Module Care ==
 
The motherboard carries '''14 or 16 × 8 KB ROS modules'''. These are normally:
 
* '''Mostek MK36000''' — most common; '''now a leading failure mode'''. Mostek mask ROMs of this era degrade with age. Symptoms: system halts mid-IPL or fails one or more PID-1200 ROS tests.
* '''Motorola 68366''' — alternative; more reliable.
* '''Motorola 68766 EPROM''' — used on early-production boards because of supply shortages.
 
If a ROS test fails repeatedly, the canonical community workaround is a '''ROM-adapter card with re-burned firmware''' — restorer-published ROM images exist on the Vintage Computer Federation forums.
 
== RAM Card Care ==
 
The 5322 RAM lives on '''one or two memory daughter cards''' via 36-pin card-edge connectors. Cards come in '''32 KB''' and '''64 KB''' sizes. Combinations:
 
* 32 KB total — 32 KB card in base slot
* 64 KB total — 64 KB card in base slot, or two 32 KB cards
* 96 KB total — 64 KB + 32 KB
* 128 KB total — 64 KB + 64 KB
 
'''The base slot must always be populated''' — the system will not boot without it.
 
The DRAMs are '''TMS4132''' — TI's factory-piggybacked variant of the TMS4116, with '''two TMS4116-class dies stacked''' in a single package. This is often mistaken for IBM-soldered redundancy; it is a TI factory part. '''Failure of either die kills the byte''' — to bench-test a TMS4132 you must physically separate the upper die from the lower die. This is normally not worth doing in a hobbyist restoration; replace the whole card with a known-good donor or modern reproduction.
 
== Connector Care ==
 
* '''Keyboard cable''' — multi-pin proprietary; clean both sides with deoxidising contact cleaner.
* '''Serial port (USART)''' — current-loop or RS-232 depending on submodel; verify before connecting external equipment.
* '''Printer ports''' (up to two) — IBM-proprietary connector pinout per SY34-0171-0.
* '''External 5246 / 5247 cable''' — IBM-proprietary card-edge cable; clean and reseat both ends.
* '''Diagnostics probe port''' (rear) — 8-bit data plus probe power; cleaned only when in use with a service-engineer probe.
 
== Recommended Tools ==
 
* Philips #2 and T15 / T20 Torx screwdrivers.
* Anti-static strap.
* Digital multimeter, plus a 0.22 µF / 50 V capacitor for IBM's ripple check.
* A high-voltage probe for the CRT. '''IBM publishes no anode voltage for this tube'''; the "12–15 kV" figure that used to be on this page had no source and has been removed. Treat it as lethal regardless.
* High-voltage probe for CRT discharge.
* IPA + foam swabs.
* Soldering iron (fine tip) + solder wick.
* Modern 8-inch floppy drive belt replacement.
* IBM keycap removal tool (same as Model F PC AT keyboard).
* SY34-0171-0 PDF.
* Service probe with 8-bit LED display (build instructions in SY34-0171-0).
* Modern ROM adapter for replacing failed Mostek MK36000 ROS modules (community-built).
 
== Related Pages ==
 
* [[IBM System/23 Datamaster]]
* [[IBM System/23 Datamaster Troubleshooting Guide]]
* [[IBM System/23 Datamaster Capacitor Replacement Guide]]
* [[IBM 5120 Maintenance Guide]] — predecessor with related linear PSU caveats
* [[IBM 5322 Computer Service Manual]] &middot; [[IBM System 23 Diagnostic User Guide]] — both hosted here


== References ==
== References ==


<references />
<references />
=== Further reading ===
* [http://bitsavers.org/pdf/ibm/system23/fe/SY34-0171-0_IBM_5322_Computer_Service_Manual_Dec80.pdf IBM 5322 Service Manual SY34-0171-0 (December 1980)].
* [http://bitsavers.org/pdf/ibm/system23/fe/6841631_System_23_Diagnostic_User_Guide_Apr82.pdf System/23 Diagnostic User Guide 6841631 (April 1982)].
* [https://bitspassats.com/index.php/IBM_System/23_Datamaster Bits Passats — IBM System/23 Datamaster]. The most thorough community technical reference.
* [http://oldcomputers.net/ibm5322.html oldcomputers.net — IBM 5322 System/23 Datamaster].
* [https://www.nf6x.net/2014/09/ibm-5322-system23-datamaster-internals/ Mark Blair (NF6X) — IBM 5322 System/23 Datamaster Internals]. Restorer's hands-on photos and notes.
* [https://forum.vcfed.org/index.php?threads/ibm-system-23-datamaster.1242319/ Vintage Computer Federation — IBM System/23 Datamaster thread].
* [https://forum.vcfed.org/index.php?threads/ibm-5322-system-23-help-needed-rom-image.65070/ VCFed — IBM 5322 ROM image thread].


{{Navbox-IBMComputers|state=collapsed}}
{{Navbox-IBMComputers|state=collapsed}}

Revision as of 22:42, 30 September 2026

IBM System/23 Datamaster 5322

This guide covers maintenance of the IBM System/23 Datamaster 5322, the one-piece desk-top unit with a built-in display, keyboard and up to two 8-inch diskette drives. It follows IBM's 5322 Computer Service Manual (SY34-0171-0) and Diagnostic User Guide (PN 6841631). The floor-standing 5324 has its own service manual (SY34-0241-1), which is on bitsavers.[1]

⚠️ Safety

IBM's DANGER notice: up to 800 V AC is generated in the power supply. Before removing the supply or any part of it, switch off the 5322 and disconnect the power cable from the outlet.[2]

  1. Switch off and unplug the 5322 before removing any cover.
  2. The power supply slides out of the rear into a service position. To switch on with the supply in that position, IBM first has the engineer check grounding continuity between the 5322 main base plate and the power supply frame with the meter on the ohms RX1 range.[2]
  3. Follow the CRT Discharge Procedure before working near the display unit.
  4. Each diskette drive has an AC drive motor with a capacitor. IBM warns that high voltage may be present at the capacitor terminals and discharges it by shorting the terminals with an insulated screwdriver before disconnecting the motor leads.[3]

See also Recommended Tools and Battery Explosion, Capacitor or Corrosion Damage.

Documentation

  • IBM 5322 Computer Service Manual, SY34-0171-0 (December 1980): locations, removal and adjustment procedures, theory of operation and parts catalogue for the 5322, its power supplies, keyboard, display and internal diskette drives. Hosted here.
  • IBM System 23 Diagnostic User Guide, PN 6841631 (April 1982): the power-on test (PID 1200), the ROS-resident diskette test (PID 1500) and the diskette-resident diagnostic and utility programs. Hosted here.
  • On bitsavers: the 5324 Computer Service Manual (SY34-0241-1, May 1982), the 5324 maintenance analysis procedures, the August 1981 edition of the Diagnostic User Guide and the 5247 Disk Unit Service Manual (SY34-0243-0).[1]

IBM's own tool list for the System/23 is the CE meter (PN 1749231), the GLP II logic probe (453212), the metric tool kit (1749235), a plastic CRT adjustment screwdriver (460811), and at branch level a ROS module puller (1715889), a module pin aligning tool (453473), a ground check tool (9900453) and a Tektronix 465 or equivalent oscilloscope.[4] The ripple check below also needs a 0.22 µF, 50 V capacitor.

Opening the 5322

IBM's cover procedures (item 1220):[5]

  • Rear access cover: pull it toward the rear until the pressure latches release.
  • Top cover: remove the rear access cover and two screws, then pull the top cover toward the rear to free the front locating tabs.
  • Keyboard cover: remove two screws, lift the front edge and pull it forward.
  • Front cover: remove the rear access, top and keyboard covers and the keyboard (item 1330), put the power supply and planar board in their service positions, pull off the brightness knob (it is keyed to its shaft), turn the diskette latches horizontal, then remove five screws from the main support plate and centre bracket and 11 screws from the bottom cover.

CPU planar board drawer

The CPU planar board sits in a drawer at the rear. Remove the rear access cover, take the I/O cables out of the ground clamp, remove the two screws at the rear of the drawer and slide it out to its service position. In that position the attachment cards, cables, CE test pins and feature jumper pins are accessible. When a planar board is replaced, move each feature jumper to the same position on the new board, and afterwards check the display's horizontal centering adjustment (item 1440).[6]

Power supply

Remove the rear access cover and top cover, open the ground clamp and take out the I/O cables, remove the two screws at the rear of the supply and slide it out. The fuses, voltage test points and power switch can be reached in this service position. To remove the supply completely, unplug P1 to P5 and the diskette attachment cable voltage wires, and replace any cable ties that had to be cut.[2]

Planar board jumpers and storage

The CPU planar diagram shows these jumper positions:[6]

  • A1: CE loop on test. A2: CE stop on error. A3: machine update card installed.
  • B1 to B5: country select. C2: internal diskette not installed. A separate jumper is fitted on 50 Hz machines only.
  • IBM warns that other jumper pins on the planar are for manufacturing use and are not jumpered in normal operation.

Read/write storage is on one or two cards in the base and feature sockets. The base socket is always used.[6]

5322 storage cards and 64K card jumpers (SM p. 2-17)
Total storage Feature socket Base socket 64K card jumpers
32K - 32K -
64K 32K 32K -
64K - 64K 1 and 3
96K 32K 64K 2 and 4
128K 64K 64K 2 and 4

The power-on test checks storage in 16K blocks as routines 2A to 30. Routines 2A, 2D and 2E cover the base socket and 2B, 2C, 2F and 30 the feature socket.[7]

Power supply checks

A 5322 has either a ferroresonant supply or a transistor-switching-regulator (TSR) supply; IBM describes them as functionally interchangeable. Both give -5, +5, -12, +12 and +24 V DC and 120 V AC for the diskette motors, display and fan. The power-good LED, visible from the rear of the supply, is lit when -5, +5, -12 and +12 V are within about 80 % of nominal.[8]

Measure at the power supply A1 card, where IBM's tolerances apply:[9]

IBM 5322 DC outputs: tolerance, ripple limit and fuse
Output Tolerance Ripple, peak to peak Fuse
+5 V +4.6 to +5.5 V 0.12 V F5, 10 A
-5 V -4.6 to -5.5 V 0.05 V F1, 0.5 A
+12 V +11.0 to +13.2 V 0.175 V F2, 1.5 A
-12 V -11.0 to -13.2 V 0.12 V F3, 0.5 A
+24 V +22.0 to +26.4 V 0.325 V F4, 1.5 A
Power good +2.4 to +5.5 V 0 -

To check ripple without an oscilloscope, put a capacitor of 0.22 µF or more (50 V DC or higher) in series with one lead of the meter, set the 2.5 V AC range, and connect between the output and frame ground. If the pointer moves off zero, excess ripple may be present.[9]

The five fuse ratings are the same on all three documented supplies. IBM checks a fuse for continuity on the ohms RX1 range and warns never to fit one of a higher rating.[10] The US and Canada supply has AC input fuse F6, 5 A slow-blow;[11] the GBG/I supplies have circuit breaker CB1 instead.[8]

Mains voltage taps

The three documented supplies are PN 6838279 (60 Hz, Canada and US), PN 6838280 (60 Hz, GBG/I) and PN 6838281 (50 Hz, GBG/I). The two GBG/I supplies are set for the local mains by the line connection and jumpers on the transformer terminal board T1/TB; IBM's diagrams show both wired for 220 V. To change the setting, measure the outlet voltage, put the supply in the service position and rewire T1/TB from the chart. For a supply with a different part number, IBM says to follow the labels on the supply.[12]

T1/TB settings, GBG/I supplies (SM pp. 2-9, 2-10)
Mains PN 6838280 (60 Hz) line PN 6838280 jumpers PN 6838281 (50 Hz) line PN 6838281 jumpers
100 V 1-7 1-6, 2-7, 4-9 1-6 1-5, 2-6, 4-8
110 V 1-8 1-6, 3-8, 4-9 1-7 1-5, 3-7, 4-8
120 V 1-9 1-6, 4-9 - -
127 V 1-10 1-6, 5-10, 4-9 - -
200/208 V 1-7 2-6 1-6 (200 V) 2-5
220 V 1-8 3-6 1-7 3-5
230 V - - 1-8 3-5
240 V 1-9 4-6 1-8 4-5

Display

The CRT display unit has a 305 mm (12 in.) screen showing 24 lines of 80 characters. IBM warns against running the 5322 with the brightness control fully clockwise for long periods, because the screen could be damaged.[13]

Diskette drives

The internal drives are the 31SD (one read/write head) and the 51TD (two heads); they differ only in the head/carriage assembly and the drive control card. IBM's maintenance preface says:[14]

  • There is no preventive maintenance for the diskette drive. Repairs are adjustments and FRU replacements directed by the MAPs, verified with the diagnostics.
  • The head/carriage assembly can be replaced in the field, but "do not repair or clean any part of this assembly".
  • The drive hub and pulley assembly is adjusted at the factory and is not field-replaceable; if it or the track 40 adjustment surface is damaged, replace the whole drive.
  • Keep television sets, display terminals and other electromagnetic devices at least 0.61 m (2 ft) from the 5322.

The drive motor turns the hub through a belt (item 1552). When refitting the motor fan and pulley, IBM sets a 0.5 mm (0.020 in.) gap between the motor and the fan hub, with the setscrew on the flat of the shaft, and fits the fan enclosure so the belt sits in its recess.[15]

On the 31SD, the head load arm carries a pressure pad. IBM replaces it when it has worn level with the arm, using kit 2200751 (which includes pad tool 2200750). Old adhesive is cleaned off the arm's mounting surface with tissue moistened with isopropyl alcohol; the head itself is not cleaned. IBM warns not to touch the pad surface or let the arm hit the read/write head.[16]

Diskettes should be kept at 10 to 51 °C and 8 to 80 % relative humidity, stored flat in their envelopes in stacks of up to ten, and kept away from heat and sunlight.[17]

Keyboard

The keyboard has 83 keys over a capacitive matrix, scanned by a microprocessor on the keyboard card, which sends a scan code and an interrupt request to the processing unit. The complete keyboard assembly is one field-replaceable unit.[18] At power-on, routine 35 resets the keyboard; its processor runs its own test and replies X'2A55', or X'552A' if the test failed.[19]

References

  1. ↑ 1.0 1.1 bitsavers, ibm/system23/fe (retrieved 2026-09-30): SY34-0171-0 5322 Computer Service Manual, SY34-0241-1 5324 Computer Service Manual (May 1982), Diagnostic User Guide 6841631 (August 1981 and April 1982 editions), 5324 MAPs; and ibm/system23/5247: SY34-0243-0 5247 Disk Unit Service Manual (April 1982).
  2. ↑ 2.0 2.1 2.2 IBM, IBM 5322 Computer Service Manual, SY34-0171-0 (December 1980), item 1240, p. 2-21, power supply removal and replacement (hosted here).
  3. ↑ IBM 5322 Computer Service Manual, SY34-0171-0, item 1551, p. 5-40.
  4. ↑ IBM, Diagnostic User Guide 0001, System/23 with Diskette, PN 6841631, EC 327594 (April 1982), section 11, pp. 17-18 (hosted here).
  5. ↑ IBM 5322 Computer Service Manual, SY34-0171-0, item 1220, p. 2-14, covers.
  6. ↑ 6.0 6.1 6.2 IBM 5322 Computer Service Manual, SY34-0171-0, item 1230, pp. 2-16 and 2-17, CPU planar board removal, replacement and diagram.
  7. ↑ IBM, Diagnostic User Guide 0001, PN 6841631, section 21.4.1.11, p. 79.
  8. ↑ 8.0 8.1 IBM 5322 Computer Service Manual, SY34-0171-0, p. 2-57, "Power supplies".
  9. ↑ 9.0 9.1 IBM 5322 Computer Service Manual, SY34-0171-0, item 1211, p. 2-11, DC voltage distribution diagram.
  10. ↑ IBM 5322 Computer Service Manual, SY34-0171-0, items 1241 (p. 2-22), 1251 (p. 2-29) and 1261 (p. 2-35).
  11. ↑ IBM 5322 Computer Service Manual, SY34-0171-0, item 1241, p. 2-23.
  12. ↑ IBM 5322 Computer Service Manual, SY34-0171-0, item 1210, pp. 2-9 and 2-10 (AC voltage charts), and items 1250 and 1260, pp. 2-28 and 2-34 (AC line voltage selection).
  13. ↑ IBM 5322 Computer Service Manual, SY34-0171-0, pp. 2-41 (standard features) and 2-43 (operator controls).
  14. ↑ IBM 5322 Computer Service Manual, SY34-0171-0, p. 5-3, maintenance preface.
  15. ↑ IBM 5322 Computer Service Manual, SY34-0171-0, item 1552, p. 5-41.
  16. ↑ IBM 5322 Computer Service Manual, SY34-0171-0, item 1531, p. 5-29.
  17. ↑ IBM 5322 Computer Service Manual, SY34-0171-0, pp. 5-62 and 5-63, diskette handling.
  18. ↑ IBM 5322 Computer Service Manual, SY34-0171-0, p. 3-16, keyboard data flow.
  19. ↑ IBM, Diagnostic User Guide 0001, PN 6841631, section 21.4.1.16, p. 80.


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