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Schematics V5.0

Listed below are schematic diagrams for many HP handheld and desktop calculator products. These diagrams were produced by dismantling and reverse-engineering the machines, and are not endorsed or supported by Hewlett-Packard in any way.

These diagrams are intended to aid electronically-knowledgable owners in repairing their machines. They are not intended as an introduction to calculator repair, and beginners will almost certainly need to refer to standard books on electronics before they can understand them. Also, many of the devices described here use lethal voltages (including the AC mains), and it is essential to know what you are doing and to take great care before attempting to repair such devices. If in doubt, ask before working on such machines.

These diagrams are offered in good faith, however it would be extremely surprising if there were no errors. Neither the author nor HPCC will be held liable for any loss or damage that results from using the information on this disk.

You can download the complete zip file of schematics for offline browsing.

DrARD 2015

Notes on particular machines and diagrams


In many cases IC power connections and decoupling capacitors are not shown on the diagrams.

'Obvious' cable wiring diagrams, such as straight-through ribbon cables, mains leads, and the like, are not included here.

Unless otherwise specified, these diagrams apply to UK versions of the machines. Voltage selectors are shown set to the 240V position, the mains fuse shown is that for 240V mains.

In some cases, particularly in power supply and tape drive circuits, 'select on test' resistors were used to compensate for tolerances elsewhere in the machine. The values shown were those present in the particular machine which was used for producing these diagrams.


Two versions of the CPU board have been seen in these machines : the older one using 2102 RAMs and 2K byte ROMs (which can take a memory expansion card on top of the board at the rear); the later one using 2114 RAMs and 8K byte ROMs. Schematics of both are included.


This machine has many PCBs in common with the HP910. The HP9820 schematics only cover those parts that are unique to this machine -- the keyboard, display, memory box and I/O backplane. For all other sections, refer to the HP9810 diagrams. The first page of the 9820 diagrams explains this in more detail.


The CPU in this machine consists of the same 4 boards that are used in the HP9810, which is why these pages have the latter's model number in the title.


Two versions of the logic board have been found, the earlier one uses a hybrid circuit containing 7 ROM chips, the later one uses 2 DIL-packaged 'Quad ROMs'. Schematics for both are included.

HP87, HP87XM

The only difference between these machines is the Logic 1 PCB. The other PCB schematics apply to both machines

Spice Series (HP31E, HP32E, HP33E, HP33C, HP34C, HP37E, HP38E, HP38C)

These machines follow one of 2 basic schematics, one for the -E models, the other for the -C models. The memory and processor chips, and the keyboard layout, are of course different between the various machines in this family, but the connections between them, and the power supply board schematic is the same. This disk contains the HP32E and HP33C schematics as being representative of these machines.


This machine has 5 preset potentiometers on the logic board. These are identified as VR1...VR5 on the schematic, they are numbered from the left side of the machine

HP11202, HP11203, HP98133, HP98134 interfaces

These interfaces were originally supplied with an un-terminated device cable, which was intended to be wired by the user to suit their device. The diagrams on this disk show the cables 'as found' (since the interfaces were obtained second-hand and had presumably been used previously) and ARD's wiring to general purpose connectors. Neither is likely to match the wiring of other examples of these interfaces.


This tape drive exists in at least 5 versions having 1..5 PCBs (+ PSU and front panel). These diagrams cover the 3-board (SBCont + Read/Write + Servo) and 1-board (Logic) versions. Others may be added if I obtain them

HPIB Disk and Tape units

Various PSUs and fans have been used in these units. Each set of diagrams includes the PSU(s) and Fan(s) that have been found in the particular device. However, if your PSU is not shown, it is worth checking other disk or tape drives.


HP110HP Portable
HP120CP/M machine
HP120KEYNotes on making a keyboard for the HP120
HP150HP150 Touchscreen PC
HP50960SRM server
HP86Bdesktop computer, external video monitor"
HP87HP87 and HP87XM desktop computers
HP9100BFirst generation RPN desktop Part 1
HP9100BFirst generation RPN desktop Part 2
HP9100BFirst generation RPN desktop Part 3
HP9100BFirst generation RPN desktop Part 4
HP9810Second generation RPN desktop
HP9815RPN desktop calculator
HP981668000-based computer with internal monitor
HP981768010-based 'shoebox'
HP9820First Algebraic desktop
HP9825First HPL desktop (also covers 9831 BASIC desktop)
HP982636HP9826 and HP9836 68000 computers
HP9830First BASIC desktop
HP9845BDesktop Computer, Opt 200 High speed language processor
HP98780Enhanced mono monitor for HP9845B
HP9915Industrial control computer (based on HP85)
INTEGRALPortable unix machine
HP35First handheld scientific
HP45Second handheld scientific
HP55Scientific with timer
HP65First handheld programmable
HP67Handheld programmable
HP70Simple financial handheld
HP80Financial handheld
HP48SX KeyboardHP48SX keyboard matrix
HP46Printing 45
HP81Printing 80 (with many more functions)
HP32ENon-continuous memory Spice (other 3xE are similar)
HP33CContinuous memory Spice (other 3xC are similar)
HP10APrinting adding machine
HP19CProgramming printing calculator
HP91Printing scientific calculator
HP92Printing financial calculator
HP95CNever-released printing programmable calculator
HP97SIOI/O module part of HP97S
HP16CProgrammer's calculator
HP21Scientific calculator
HP22Financial calculator
HP25Programmable calculator
HP25CContinuous memory programmable calculator
HP27Financial and scientific calculator
HP29CContinuous memory programmable calculator
HP11305 MicrocodeHP11305 disk controller source listing
HP11305 Output SignalsList of signals produced by HP11305 control system
HP9800 CPU MicrocodeHP9800 CPU microcode source listing
HP9866A State MachineHP9866a printer state machine listing
HP50962DIO SRM Coax interface
HP98204ADIO TV-rate video interface
HP98204BDIO Video board (including graphics)
HP98259DIO 128K Bubble memory PCB
HP98604ROM HPL PCB for HP9000/200 machines
HP98620BDIO DMA controller
HP98622DIO GPIO board
HP98624DIO HPIB Interface
HP98626DIO RS232 Interface
HP98628DIO RS232 Interface (Z80 controlled)
KBD9920HP9920 keyboard interface/HPIB PCB
WKBP4A3rd party 256K DIO RAM board
HP112028 bit parallel interface for HP98x0
HP11203BCD interface for HP98x0
HP11205RS232 interface for HP98x0
HP11206Modem interface for HP9830
HP11284Datacomms interface for 9830
HP11305Disk Controller for HP9830
HP11336Printer interface (HP9871) for HP98x0
HP13264Data link interface
HP13267First multipoint interface
HP45632384K RAM PCB for HP150
HP45643Parallel/HPIL PCB for HP150
HP45890Expanded RAM PCB for HP150
HP45915384K RAM/HP-HIL PCB for HP150
HP2623Graphics terminal
HP2631BDot matrix printer
HP2671GHPIB Thermal printer
HP2674Internal thermal printer
HP27201HPIB extender
HP2748AOptical paper tape reader
HP35731Monochrome monitor for HP9000/200 machines
HP46020First type HP-HIL keyboard
HP46021Second type HP-HIL keyboard
HP46083HP-HIL knob input device
HP5055Digital Recorder (strip printer)
HP59301HPIB parallel interface
HP59303HPIB input DAC
HP59304HPIB remote display unit
HP59306HPIB relay actuator
HP59308HPIB timing generator
HP59309HPIB digital clock
HP59313HPIB interfaced ADC
HP59401HPIB analyser
HP59403HPIB common carrier interface
HP59405HPIB interface for HP9830
HP59500HPIB interface for HP6940 multiprogrammer
HP7225BFlatbed plotter, HPIB and RS232 models"
HP7245AThermal printer/plotter
HP7440 HPIBHPIB ColourPro plotter
HP7470 OPT003HPIL Plotter
HP7475HPIB Plotter
HP7959BHPIB hard disk unit (ESDI drive)
HP82104Card reader for HP41
HP82143Dedicated thermal printer for HP41
HP82153Barcode Wand for HP41
HP82162HPIL thermal printer
HP82168HPIL modem
HP82440AIR thermal printer
HP82440BIR thermal printer
HP82901Dual 5.25"" disk drive"
HP8290316K RAM module for HP85
HP82905Dot matrix printer (either HPIB or HPIL)
HP82909128K RAM module for HP86/87
HP82913Monochrome monitor (NEC chassis)
HP82936ROM Drawer for HP80-series
HP82985Portable Plus video interface
HP9114AHPIL disk drivc
HP9114BHPIL disk drive
HP9121Single-sided 3.5" HPIB floppy drive
HP9122Double-sided 3.5" disk drive
HP9123HPIB floppy drive for the HP150-II
HP9125APlotter for HP9100
HP9133HHPIB hard/floppy disk unit
HP9133VXVHP913V, HP9133XV hard/floppy disk units
HP9142QIC tape drive
HP914416 track cartridge tape drive
HP914532 track cartridge tape drive
HP9154BHPIB hard disk unit (Nighthawk drive)
HP98033BCD interface for HP9825
HP98034HPIB interface for HP9825
HP98035Real time clock module for HP9825
HP98036RS232 interface for HP9825
HP98046Data Communication interface for HP9845
HP98133BCD interface for HP9815
HP98134GPIO interface for HP9815
HP98228Bank-switched disk ROM module for HP9825
HP9862IFPlotter interface (only) for HP98x0
HP9865Cassette drive for HP98x0 -- Interface ONLY
HP9866Thermal printer for 9800-series
HP9877External tape drive for HP9825
HP9878Expansion chassis for HP9825
HP82904Expansion interface for Integral
HP82915Modem PCB for Integral
HP82916RAM PCBs for Integral
HP82919RS232 interface for Integral
HP82971ROM/EPROM module for Integral
HP69321B12-bit voltage D/A for multiprogrammer
HP69330ARelay output for multiprogrammer
HP69351Voltage regulator for multiprogrammer
HP69422AHigh-speed A/D for multiprogrammer
HP69431ADigital input for multiprogrammer
HP69502AResistance program for multiprogrammer
PAINTJETColour inkjet printer
RSUEramco MLDL unit for HP41
RSU2Eramco MLDL for HP41 (card reader case)
WAND75DWand for the HP75D
ERAMCO_PPPortable Plus car charger (Eramco)
HP82028Woodstock charger
HP82054Car charger
HP82055Woodstock car charger

Page Last modified: 1st January 2022