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IBM PC XT/370 Capacitor Replacement Guide: Difference between revisions

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Rebuild from IBM SA38-0037-00: removed all three invented card capacitor tables (IBM publishes nothing below card level for the 370 cards); corrected the card names and count - IBM says two cards, PC/370-P in slot 4 and PC/370-M in slot 3, with PC/3277-EM only on older models (5160 Models 568/588/589); removed the invented 'matched set' backplane-connector claim and the 5151/5153 CRT paragraph; fixed the red link to the XT guide; cleared Unverified data
Rewrite: card FRUs from IBM parts list (P-M cable 8654374 is an XT/370 part, not AT/370); IBM supply limits; remove self-reference, fish-smell/replace-immediately line and appeal to publish; fix links to renamed XT headings
 
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[[File:IBM XT 370 board.jpg|thumb|320px|The PC/370-P processor card of an IBM PC XT/370. (Image: Wikimedia Commons)]]


The '''[[IBM PC XT/370]]''' is an [[IBM PC XT (5160)|IBM PC XT]] with System/370 emulation cards in it. IBM describes it as "an extended version of the 5160 XT with 256Kb of memory on the system board", and lists the cards as standard features of '''5160 Models 568, 588 and 589''' in the 5160 chapter of its own service manual.<ref name="sim">IBM, ''IBM Personal Computer Family Service Information Manual'', SA38-0037-00, July 1989. Chapter 6, "5160 PC XT": the 5160 model feature chart (which lists the PC/370-M, PC/370-P and PC/3277-EM cards against particular 5160 models), the power supply description, and the "5160 XT/370" pages covering the card complement, slot assignments and unit specifications. Chapter 18 lists the AT/370 card part numbers. Hosted on this wiki as [[IBM Personal Computer Family Service Information Manual]].</ref>
The '''[[IBM PC XT/370]]''' is an [[IBM PC XT (5160)|IBM PC XT]] with System/370 cards added, sold as 5160 models 568, 588 and 589.<ref name="sim">IBM, ''Personal Computer Family Service Information Manual'', SA38-0037-00, First Edition, January 1989, hosted as [[:File:IBM Personal Computer Family Service Information Manual SA38-0037-00.pdf]]. Chapter 6: 5160 model feature chart and power supply description (p. 6-2); "5160 XT/370" (pp. 6-17 to 6-19). Chapter 18: XT/370 parts (p. 18-19).</ref> The system board and power supply are the XT's, so the recapping work is on the [[IBM PC XT Capacitor Replacement Guide]]: sixteen tantalums on the board, thirteen of them on +5 V, C56 on +12 V, and 10 µF 16 V as the replacement part.<ref name="mz5v">[https://www.minuszerodegrees.net/5150_5160/MDC/tantalum_short_plus_5volts.htm Short-circuit on the +5 volt line of an IBM 5150/5155/5160 motherboard], minuszerodegrees.net.</ref><ref name="mz12v">[https://www.minuszerodegrees.net/5150_5160/MDC/tantalum_short_plus_12volts.htm Short-circuit on the +12 volt line of an IBM 5150/5155/5160 motherboard], minuszerodegrees.net.</ref><ref name="mz2leg">[https://www.minuszerodegrees.net/failure/IBM%2051xx%20motherboards%20-%202-legged%20tantalum%20capacitors.htm IBM 51xx motherboards/cards – types wired to use 2-legged tantalum capacitors], minuszerodegrees.net.</ref> The XT/370 models use the 64/256 KB system board, for which IBM's service manual gives the same memory decoding as the XT and 5155.<ref name="sim4">IBM, ''Personal Computer Family Service Information Manual'', SA38-0037-00 (1989), chapter 4, pp. 4-3 to 4-6.</ref>


'''There is therefore no separate capacitor procedure for this machine.''' The chassis, system board and power supply are the XT's, and the work is documented in full, against board photographs, on the '''[[IBM PC XT Capacitor Replacement Guide]]''' &mdash; sixteen tantalums on the board, thirteen of them on the +5 V line, C55 a ceramic and C56 a tantalum as the only two components on +12 V, 10 &micro;F / 16 V as the replacement part throughout, and the SNCTOL cut-and-graft technique for getting them out without lifting pads.<ref name="mz5v">[https://www.minuszerodegrees.net/5150_5160/MDC/tantalum_short_plus_5volts.htm Short-circuit on the +5 volt line of an IBM 5150/5155/5160 motherboard], minuszerodegrees.net. Source for the count of sixteen tantalum capacitors on the 5160 motherboard and the thirteen on the +5 volt line.</ref><ref name="mz12v">[https://www.minuszerodegrees.net/5150_5160/MDC/tantalum_short_plus_12volts.htm Short-circuit on the +12 volt line of an IBM 5150/5155/5160 motherboard], minuszerodegrees.net. Source for the statement that the 5160's +12 V line carries exactly two components, C55 and C56, and that C56 is not critical to motherboard operation.</ref><ref name="mz2leg">[https://www.minuszerodegrees.net/failure/IBM%2051xx%20motherboards%20-%202-legged%20tantalum%20capacitors.htm IBM 51xx motherboards/cards &mdash; types wired to use 2-legged tantalum capacitors], minuszerodegrees.net. Gives the replacement value as 10 &micro;F rated at 16 volts, with a higher rating acceptable.</ref>
== The XT/370 cards ==
 
Read that page. This one exists only to record the three things that are specific to an XT/370: '''which cards are fitted and where''', '''what the supply has left to give once they are in''', and '''what is and is not published about the cards themselves'''.
 
[[File:IBM XT 370 board.jpg|center|thumb|480px|One of the System/370 emulation cards from an IBM XT/370. IBM published no component-level parts list for any of these cards. (Image: Wikimedia Commons)]]
 
== The cards, and which slots they occupy ==
 
IBM's own description of the machine:<ref name="sim" />


{| class="wikitable styled-table" style="width:100%;"
{| class="wikitable styled-table" style="width:100%;"
|+'''IBM PC XT/370 &mdash; card complement'''
|+'''XT/370 cards (IBM service manual pp. 6-17 to 6-19 and 18-19)'''
! Card !! Slot !! What IBM says it does
! Card !! IBM FRU !! Slot !! IBM's description
|-
|-
| '''PC/370-P''' (Processor card) || Expansion slot '''4''' || "The centre of the S/370 operations for the PC XT/370. Contains the microprocessors and control circuits that enable the PC XT/370 to execute S/370 instructions."
| PC/370-P processor card || 8654372 || 4 || "the center of the S/370 operations for the PC XT/370"; contains the microprocessors and control circuits that execute S/370 instructions
|-
|-
| '''PC/370-M''' (512 KB Memory card) || Expansion slot '''3''' || "Contains 512Kb of parity-checked random access memory, which can be used by either the PC/370-P card or by the PC XT. This provides 512Kb of memory for use in S/370 mode, or a total of 640Kb of memory for use in PC XT mode."
| PC/370-M memory card || 8654371 || 3 || 512 KB of parity-checked RAM, used by the PC/370-P or by the XT
|-
|-
| '''PC/3277-EM''' (optional; older models) || &mdash; || 3277-2 terminal emulation when the XT/370 is linked to a host system, plus screen and listing printing and file transfer between the XT/370 and host disks
| PC/370-P-M cable || 8654374 || || Joins the two cards
|-
|-
| '''Remote Display Terminal Device Emulation Adapter''' (optional) || May be in expansion slot '''2''' || Terminal emulation
| PC/3277-EM card || 8654373 || || 3277-2 emulation when linked to a host (models 568 and 588)
|-
| '''IBM 3278/79 Emulation Adapter''' (optional) || &mdash; || Host connection
|}
|}
Source: IBM service manual.<ref name="sim" />


Against IBM's 5160 model feature chart, the PC/370-M and PC/370-P cards are standard on '''Models 568, 588 and 589''', and the PC/3277-EM card on '''Models 568 and 588'''.<ref name="sim" />
IBM's service documents treat each card as a single field-replaceable unit. They give no parts list, capacitor positions or schematic for the PC/370-P, PC/370-M or PC/3277-EM.<ref name="sim" />


'''Note the card count.''' IBM's text says the system unit has '''two''' XT/370 adapter cards plugged into the system board, with the PC/3277-EM as a third on older models and the other emulation adapters as options. A machine with three 370 cards in it is a particular model, not the universal configuration &mdash; check what is actually fitted before ordering anything or assuming a card is missing.
== Supply loading ==


The XT/370 can be a 10 MB system with one fixed disk in the system unit, or a 20 MB system with two fixed disks in a 5161 Expansion Unit.<ref name="sim" />
IBM rates the 5160 supply for continuous operation at 130 W. The system board takes about 2 to 4 A of the 15 A available on +5 V, leaving about 11 A for the cards in the slots.<ref name="tr">IBM, ''Personal Computer XT and Portable Personal Computer Technical Reference'', part 6139821, March 1986, pp. 3-3 to 3-5, hosted as [[:File:IBM PC XT 5155 5160 Technical Reference Mar86.pdf]].</ref> On an XT/370 that 11 A is shared by the full-length processor and memory cards, the emulation card, and the diskette, fixed disk and display adapters.


== What the supply has left ==
The supply switches all its outputs off while a DC overcurrent or overvoltage exists, so a shorted tantalum on the system board or on any card makes the whole machine look dead.<ref name="tr" /> To find it:


This is the one place where the XT/370 genuinely differs from a plain XT for power work, and it is a matter of headroom rather than of different components.
# Start from the minimum diagnostic configuration: system board, supply and speaker only.<ref name="mzmdc">[https://www.minuszerodegrees.net/5150_5160/MDC/minimum_diag_config.htm IBM 5150/5155/5160 – Minimum Diagnostic Configuration], minuszerodegrees.net.</ref>
# If the supply still shuts down, the short is on the system board; follow [[IBM PC XT Capacitor Replacement Guide#Finding a short-circuit tantalum|the XT procedure]].
# If the board runs, refit the cards one at a time, switching off between each. Keep the PC/370-P and PC/370-M together with their cable. The card that makes the supply shut down has the short.


IBM's figures for the 5160 supply: it is '''designed for continuous operation at 130 watts'''; there are two supplies, 120 V AC and 220/240 V AC, both fused; and if DC overcurrent or overvoltage conditions exist, the supply automatically shuts down until the condition is corrected. '''The system board takes approximately 2 to 4 A of +5 V DC, leaving approximately 11 A of +5 V DC for the adapters in the system expansion slots.''' The +12 V level powers the diskette drive and the 10 MB fixed disk; &minus;5 V is used by the analogue circuits in the diskette adapter's phase-lock loop; +12 V and &minus;12 V drive the EIA line drivers on the communications adapters. All four levels are bussed across the eight expansion slots.<ref name="sim" />
minuszerodegrees.net reports tantalum failures on IBM 51xx cards as well as system boards, mostly at switch-on and mostly on equipment that has not been powered for years.<ref name="mzfail">[https://www.minuszerodegrees.net/failure/failure.htm Commonly Failing Electronic Components (in vintage computers)], minuszerodegrees.net.</ref> IBM's 51xx cards use the same three-hole tantalum footprint as the system boards, wired for two or three legs; the positive leg goes in the hole marked +.<ref name="mztant">[https://www.minuszerodegrees.net/failure/IBM%2051xx%20motherboards%20-%20tantalum%20capacitors.htm Tantalum capacitors on IBM 51xx motherboards/cards], minuszerodegrees.net.</ref> Read the value and polarity off each part on the card before removing it.


On an XT/370 that 11 A is shared by two or three large full-length cards, a fixed disk adapter, a diskette adapter and a display adapter. Two practical consequences:
== Voltage checks ==


* '''A tired supply shows up on an XT/370 before it shows up on a plain XT.''' If the machine is stable with the 370 cards out and unstable with them in, measure the rails under that load before suspecting the cards.
Use IBM's limits at the system board connectors, and the Technical Reference sense levels:<ref name="sim4" /><ref name="tr" />
* '''A shorted tantalum anywhere presents the same way.''' The supply latches off, often with the fan still turning, because that is what IBM designed it to do. That is the fault to rule out first, and the method is on the [[IBM PC XT Capacitor Replacement Guide#Diagnostic Procedure for a Suspected Short-Circuit Tantalum|XT page]].


IBM's unit specification for the XT/370: heat output '''650 BTU/hr''', noise level 49.5 dBa with a monochrome display and expansion unit attached, mains nominal 120 V AC (minimum 104 V, maximum 127 V), system unit weight 14.5 kg.<ref name="sim" />
{| class="wikitable styled-table" style="width:80%; text-align:center;"
 
|+'''IBM 5160 power supply limits'''
== What is published about the cards &mdash; and what is not ==
! Rail !! Service limits !! Sense level for power good
 
|-
'''Nothing below card level, for any of them.''' IBM's service documentation for the XT/370 is FRU-level: it names the cards, says which slots they go in, and stops. There is no designator map, no parts list and no schematic for the PC/370-P, the PC/370-M or the PC/3277-EM in any document this wiki has located.
| +5 V || +4.8 to +5.25 V || +4.5 V
 
|-
The nearest thing to a parts list IBM gives in this manual is for the '''AT/370''', the 5170-based successor: PC/370-P2 card '''2684070''', PC/370-M2 card '''2684069''', PC/370-P-M cable '''8654374''', and 3278/79 Emulation Adapter '''8654378'''.<ref name="sim" /> Those are AT/370 parts and do not fit an XT/370, but the existence of a documented '''cable between the P and M cards''' on the AT/370 is worth knowing before anyone tries to lever a pair of XT/370 cards out as if they were independent.
| −5 V || −4.6 to −5.5 V || −4.3 V
 
|-
'''This page publishes no capacitor values for any 370 card, because none have been published.''' What can be said, and is sourced, is that tantalum failure is reported right across the IBM 51xx PC family with cards included, that the cards use the same 10 &micro;F / 16 V parts in the same three-hole footprint as the motherboard, and that no per-card designator map exists for XT-era adapters.<ref name="mzfail">[https://www.minuszerodegrees.net/failure/failure.htm Commonly Failing Electronic Components (in vintage computers)], minuszerodegrees.net. Source for tantalum failure across the IBM 51xx family including cards, for failures occurring at or shortly after power-on, and for the higher failure rate on boards left unpowered for years.</ref><ref name="mz2leg" />
| +12 V || +11.5 to +12.6 V || +10.8 V
 
|-
So the diagnosis is behavioural rather than by designator: if the system board alone runs cleanly but the supply latches off with a particular card fitted, that card has the short, and the same technique used on the motherboard applies to it.
| −12 V || −10.9 to −13.2 V || −10.2 V
 
|}
If you transcribe the capacitor complement of a PC/370-P or PC/370-M &mdash; designator, value, voltage, dielectric, position, with photographs and the card's IBM part number &mdash; publish it. These are rare cards and no such list appears to exist anywhere.
 
== When to recap ==
 
The triggers are the XT's, with one addition:


* Visible tantalum failure on the board or on any card &mdash; a small black hole or "eye" on the body, a cracked or scorched case, or damage to a neighbouring part. In many cases there is no visual sign at all.<ref name="mzfail" />
If the rails are in limits with the XT/370 cards out and fall out of limits with them in, refit the cards one at a time to find which one pulls the rail down.
* The supply latching off with a card fitted and coming up without it.
* A rail outside the regulation tolerances published on the [[IBM PC XT Capacitor Replacement Guide#Post-Recap Voltage Checks|XT page]].
* Instability under the full 370-card load that clears with the cards removed.
* Mains-side suppression capacitors in the supply that are cracked, discoloured or smell of fish in use. Replace immediately with correctly safety-rated parts of the same class.


Failures happen overwhelmingly on application of power or within about thirty seconds of it, and the rate is high for a board that has sat unpowered for years.<ref name="mzfail" /> Eye protection on first power-up of an unknown XT/370 is sensible, not paranoid: these cards are effectively unobtainable.
A 20 MB XT/370 has a second 130 W supply in its 5161 Expansion Unit, which needs the same checks.<ref name="sim7">IBM, ''Personal Computer Family Service Information Manual'', SA38-0037-00 (1989), chapter 7, p. 7-1.</ref>


== Related Pages ==
== Related pages ==


* [[IBM PC XT/370]] · [[IBM PC XT/370 Maintenance Guide]] · [[IBM PC XT/370 Troubleshooting Guide]]
* [[IBM PC XT/370]] · [[IBM PC XT/370 Maintenance Guide]] · [[IBM PC XT/370 Troubleshooting Guide]]
* '''[[IBM PC XT Capacitor Replacement Guide]]''' &mdash; the procedure this machine actually needs
* [[IBM PC XT Capacitor Replacement Guide]]
* [[IBM PC XT (5160)]] · [[IBM Personal Computer Family Service Information Manual]]
* [[IBM PC XT (5160)]] · [[IBM Personal Computer Family Service Information Manual]]
* [[Capacitor Failure Symptoms]] · [[Recommended Tools]]
* [[Capacitor Failure Symptoms]]


== References ==
== References ==

Latest revision as of 20:57, 30 September 2026

The PC/370-P processor card of an IBM PC XT/370. (Image: Wikimedia Commons)

The IBM PC XT/370 is an IBM PC XT with System/370 cards added, sold as 5160 models 568, 588 and 589.[1] The system board and power supply are the XT's, so the recapping work is on the IBM PC XT Capacitor Replacement Guide: sixteen tantalums on the board, thirteen of them on +5 V, C56 on +12 V, and 10 µF 16 V as the replacement part.[2][3][4] The XT/370 models use the 64/256 KB system board, for which IBM's service manual gives the same memory decoding as the XT and 5155.[5]

The XT/370 cards

[edit | edit source]
XT/370 cards (IBM service manual pp. 6-17 to 6-19 and 18-19)
Card IBM FRU Slot IBM's description
PC/370-P processor card 8654372 4 "the center of the S/370 operations for the PC XT/370"; contains the microprocessors and control circuits that execute S/370 instructions
PC/370-M memory card 8654371 3 512 KB of parity-checked RAM, used by the PC/370-P or by the XT
PC/370-P-M cable 8654374 Joins the two cards
PC/3277-EM card 8654373 3277-2 emulation when linked to a host (models 568 and 588)

Source: IBM service manual.[1]

IBM's service documents treat each card as a single field-replaceable unit. They give no parts list, capacitor positions or schematic for the PC/370-P, PC/370-M or PC/3277-EM.[1]

Supply loading

[edit | edit source]

IBM rates the 5160 supply for continuous operation at 130 W. The system board takes about 2 to 4 A of the 15 A available on +5 V, leaving about 11 A for the cards in the slots.[6] On an XT/370 that 11 A is shared by the full-length processor and memory cards, the emulation card, and the diskette, fixed disk and display adapters.

The supply switches all its outputs off while a DC overcurrent or overvoltage exists, so a shorted tantalum on the system board or on any card makes the whole machine look dead.[6] To find it:

  1. Start from the minimum diagnostic configuration: system board, supply and speaker only.[7]
  2. If the supply still shuts down, the short is on the system board; follow the XT procedure.
  3. If the board runs, refit the cards one at a time, switching off between each. Keep the PC/370-P and PC/370-M together with their cable. The card that makes the supply shut down has the short.

minuszerodegrees.net reports tantalum failures on IBM 51xx cards as well as system boards, mostly at switch-on and mostly on equipment that has not been powered for years.[8] IBM's 51xx cards use the same three-hole tantalum footprint as the system boards, wired for two or three legs; the positive leg goes in the hole marked +.[9] Read the value and polarity off each part on the card before removing it.

Voltage checks

[edit | edit source]

Use IBM's limits at the system board connectors, and the Technical Reference sense levels:[5][6]

IBM 5160 power supply limits
Rail Service limits Sense level for power good
+5 V +4.8 to +5.25 V +4.5 V
−5 V −4.6 to −5.5 V −4.3 V
+12 V +11.5 to +12.6 V +10.8 V
−12 V −10.9 to −13.2 V −10.2 V

If the rails are in limits with the XT/370 cards out and fall out of limits with them in, refit the cards one at a time to find which one pulls the rail down.

A 20 MB XT/370 has a second 130 W supply in its 5161 Expansion Unit, which needs the same checks.[10]

[edit | edit source]

References

[edit | edit source]
  1. ↑ 1.0 1.1 1.2 IBM, Personal Computer Family Service Information Manual, SA38-0037-00, First Edition, January 1989, hosted as File:IBM Personal Computer Family Service Information Manual SA38-0037-00.pdf. Chapter 6: 5160 model feature chart and power supply description (p. 6-2); "5160 XT/370" (pp. 6-17 to 6-19). Chapter 18: XT/370 parts (p. 18-19).
  2. ↑ Short-circuit on the +5 volt line of an IBM 5150/5155/5160 motherboard, minuszerodegrees.net.
  3. ↑ Short-circuit on the +12 volt line of an IBM 5150/5155/5160 motherboard, minuszerodegrees.net.
  4. ↑ IBM 51xx motherboards/cards – types wired to use 2-legged tantalum capacitors, minuszerodegrees.net.
  5. ↑ 5.0 5.1 IBM, Personal Computer Family Service Information Manual, SA38-0037-00 (1989), chapter 4, pp. 4-3 to 4-6.
  6. ↑ 6.0 6.1 6.2 IBM, Personal Computer XT and Portable Personal Computer Technical Reference, part 6139821, March 1986, pp. 3-3 to 3-5, hosted as File:IBM PC XT 5155 5160 Technical Reference Mar86.pdf.
  7. ↑ IBM 5150/5155/5160 – Minimum Diagnostic Configuration, minuszerodegrees.net.
  8. ↑ Commonly Failing Electronic Components (in vintage computers), minuszerodegrees.net.
  9. ↑ Tantalum capacitors on IBM 51xx motherboards/cards, minuszerodegrees.net.
  10. ↑ IBM, Personal Computer Family Service Information Manual, SA38-0037-00 (1989), chapter 7, p. 7-1.


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