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P4 verification: real documentation page - title as printed, part/form number, edition, contents, honest gaps, what it settles, cross-links
Title blocks and sheet 11 values rechecked on the page images; sheet 11 does show an electrolytic (C8 22 uF 25 V); remove uncited publisher history, 'IBM never published' and value-of-set puffery
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The '''PS/2 Model 50 schematic set''' is sixteen pages of circuit diagrams for the [[IBM PS/2 Model 50|PS/2 Model 50]] (8550) planar, '''Revision 4, dated 21 May to 2 June 1991'''.
<templatestyles src="Template:StyledTable/styles.css" />
The '''PS/2 Model 50 schematic set''' is a 16-page PDF of third-party logic drawings of the [[IBM PS/2 Model 50|PS/2 Model 50]] (8550) system board. The title blocks read "Maintenance Information Technology", "PS/2 50" and "COPYRIGHT APPLIED FOR"; the notice beside them names Maintenance Information Technologies, says the content was sold for the buyer's unlimited use and must not be copied for republication or distribution outside the buyer's company, and gives no warranty of accuracy. All sheets present are revision 4, dated between 21 May and 2 June 1991. The scan is image-only.


'''Sheet 1 is missing.''' Page 1 of the PDF is a placeholder reading "sheet 1 Missing from Original Set"; the scan runs from sheet 2 to sheet 16. Whatever sheet 1 covered is not here and was already absent when this set was scanned.
PDF page 1 is a placeholder reading "Sheet 1 Missing from Original Set", so the drawings run from sheet 2 to sheet 16.


These sheets are '''not an IBM publication.''' Every title block carries the name '''Maintenance Information Technologies''' and the words "COPYRIGHT APPLIED FOR", together with this notice:
== Contents ==
{| class="wikitable styled-table"
! Sheet !! Title !! Sheet !! Title
|-
| 2 || CPU || 10 || Disk I/F
|-
| 3 || Memory || 11 || Real Time Clock
|-
| 4 || Clocks || 12 || DMA I/F
|-
| 5 || Bus Connections || 13 || Video I/F
|-
| 6 || Serial I/O || 14 || Bus Connectors/B
|-
| 7 || Interrupts || 15 || I/O Control
|-
| 8 || Keyboard I/F || 16 || Bus Controller
|-
| 9 || Printer I/O || ||
|}


:''"Servicing of any electronic product should only be performed by qualified personnel. This drawing and information has been Copyrighted by the company listed. Its content has been sold for the unlimited use to you. The only restrictions are that it not be copied for republication or distribution outside your company. No patent liability is assumed with respect to the use of information contained herein. Maintenance Information Technologies believes the information herein to be correct. We are not responsible for any typographical errors; no direct or implied warranty is made to its accuracy. Specifications subject to change without notice."''
The drawings carry designators and values for the parts on each circuit. Sheet 11 shows the real-time clock ZM47, a Motorola MC146818A, with its oscillator (Y1 32.768 kHz, C17 27 pF, R16 2 MΩ and 14069 inverters ZM28A-C), the standby supply through diodes CR1 to CR6 with R10 620 Ω from +12 V, R12 1 kΩ to CKFS, R9 10 kΩ and C16 0.0056 µF on RESET. The same sheet has ZM50, a 74ALS244 that puts the diskette status lines on XD0-XD7, and an electrolytic, C8 22 µF 25 V.


Maintenance Information Technologies was a third-party publisher of service schematics for the independent repair trade in the late 1980s and early 1990s. IBM itself never published a PS/2 schematic.
== What this document does not contain ==
Sheet 1 is missing. There is no parts list, bill of materials, board layout or power-distribution sheet, so the set is not a complete capacitor list, and it does not say which board revision (Type 1 or Type 2) it was drawn from.


== What it contains ==
== Pages that cite this document ==
 
* [[IBM PS/2 Model 50]] lists it as the planar schematics.
Fifteen sheets, numbered 2 to 16, each titled "PS/2 50":
* [[IBM PS2 Model 50 Technical Reference (May 1988)]], [[IBM PS2 Model 50 Technical Reference (October 1990)]], [[IBM PS2 Model 50 Hardware Maintenance Reference]], [[IBM PS2 Model 30 Schematics]] and [[IBM PS2 Model 80 Schematics]] list it as related.
 
# ''(sheet 1 missing from the original set)''
# '''CPU'''
# '''MEMORY'''
# '''CLOCKS'''
# '''BUS CONNECTIONS'''
# '''SERIAL I/O'''
# '''INTERRUPTS'''
# '''KEYBOARD I/F'''
# '''PRINTER I/O'''
# '''DISK I/F'''
# '''REAL TIME CLOCK'''
# '''DMA I/F'''
# '''VIDEO I/F'''
# '''BUS CONNECTORS/B'''
# '''I/O CONTROL'''
# '''BUS CONTROLLER'''
 
The drawings carry designators and values. Sheet 13 (Video I/F), for instance, shows '''R68 33&nbsp;&Omega;''' and '''C175 68&nbsp;pF''' on the video output network.
 
== What it does not contain ==
 
'''No text layer.''' These are scanned drawings. `pdftotext` returns almost nothing and OCR returns garbled fragments, so read them as page images, not as text.
 
'''No parts list, no bill of materials, no board silkscreen map and no power distribution sheet.''' The component values that are shown are the ones drawn on the signal circuits themselves. Bulk electrolytics and the planar decoupling do not appear, so these sheets will '''not''' give you a recapping list &mdash; but they will give you the value of a specific resistor or small capacitor in a circuit you are tracing, which is more than any IBM publication does.
 
There is no revision history and no statement of which planar revision a Model 30 or Model 50 sheet was drawn from.
 
== What it settles ==
 
'''Sheet 11, REAL TIME CLOCK, settles the Model 50's clock circuit at component level.''' The RTC is '''ZM47, a Motorola MC146818A'''. Its oscillator is '''Y1, 32.768&nbsp;kHz''', with '''C17 27&nbsp;pF''' and '''R16 2&nbsp;M&Omega;''' round a '''14069''' inverter chain at '''ZM28A/B/C'''. The standby network is a diode chain '''CR1, CR2, CR4, CR6''' from +5&nbsp;V with '''R10 620&nbsp;&Omega;''' fed from +12&nbsp;V, '''R12 1&nbsp;k&Omega;''' to CKFS, '''R9 10&nbsp;k&Omega;''', and '''C16 0.0056&nbsp;&micro;F''' on RESET. '''ZM50''' is a 74ALS244 buffering the floppy status lines onto XD0&ndash;XD7.
 
That independently confirms what [[IBM PS/2 Model 50]] states from IBM's own documentation: the Model 50's real-time clock is an '''MC146818A with a separate lithium cell''', not a Dallas potted module. It is also the exception to the rule that no component values were ever published for these machines.


<pdf> File:IBM PS2 Model 50 Schematics.pdf </pdf>
<pdf> File:IBM PS2 Model 50 Schematics.pdf </pdf>


Download it here: [[:File:IBM PS2 Model 50 Schematics.pdf|IBM PS2 Model 50 Schematics.pdf]]
Download: [[:File:IBM PS2 Model 50 Schematics.pdf|IBM PS2 Model 50 Schematics.pdf]]
 
== Related pages ==
 
* [[IBM PS/2 Model 50]] &middot; [[IBM PS/2 Model 50 Maintenance Guide]] &middot; [[IBM PS/2 Model 50 Troubleshooting Guide]] &middot; [[IBM PS/2 Model 50 Capacitor Replacement Guide]]
* [[IBM PS2 Model 50 Technical Reference (May 1988)]] &middot; [[IBM PS2 Model 50 Hardware Maintenance Reference]]
* [[IBM PS2 Model 30 Schematics]] &middot; [[IBM PS2 Model 80 Schematics]]


[[Category:IBM Service Manuals]]
[[Category:IBM Service Manuals]]
[[Category:Service Manuals]]
[[Category:Service Manuals]]

Revision as of 21:45, 30 September 2026

The PS/2 Model 50 schematic set is a 16-page PDF of third-party logic drawings of the PS/2 Model 50 (8550) system board. The title blocks read "Maintenance Information Technology", "PS/2 50" and "COPYRIGHT APPLIED FOR"; the notice beside them names Maintenance Information Technologies, says the content was sold for the buyer's unlimited use and must not be copied for republication or distribution outside the buyer's company, and gives no warranty of accuracy. All sheets present are revision 4, dated between 21 May and 2 June 1991. The scan is image-only.

PDF page 1 is a placeholder reading "Sheet 1 Missing from Original Set", so the drawings run from sheet 2 to sheet 16.

Contents

Sheet Title Sheet Title
2 CPU 10 Disk I/F
3 Memory 11 Real Time Clock
4 Clocks 12 DMA I/F
5 Bus Connections 13 Video I/F
6 Serial I/O 14 Bus Connectors/B
7 Interrupts 15 I/O Control
8 Keyboard I/F 16 Bus Controller
9 Printer I/O

The drawings carry designators and values for the parts on each circuit. Sheet 11 shows the real-time clock ZM47, a Motorola MC146818A, with its oscillator (Y1 32.768 kHz, C17 27 pF, R16 2 MΩ and 14069 inverters ZM28A-C), the standby supply through diodes CR1 to CR6 with R10 620 Ω from +12 V, R12 1 kΩ to CKFS, R9 10 kΩ and C16 0.0056 µF on RESET. The same sheet has ZM50, a 74ALS244 that puts the diskette status lines on XD0-XD7, and an electrolytic, C8 22 µF 25 V.

What this document does not contain

Sheet 1 is missing. There is no parts list, bill of materials, board layout or power-distribution sheet, so the set is not a complete capacitor list, and it does not say which board revision (Type 1 or Type 2) it was drawn from.

Pages that cite this document

Download: IBM PS2 Model 50 Schematics.pdf

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