QL Hardware Documents section

QL Hardware  

Last Updated: 28.04.2021

Battery Backed Clock

Battery_Backed_Clock.zip - Battery Backed Clock. Notes on getting the Battery backed clock to work on the QL. Includes a screen display (LBYTES to address 131072 in mode 4) of a circuit diagram.  (Martin Head) (3K)
Or, download as a PDF file (thanks to Martyn Hill) (197K)

Build Standards, Serial Numbers, Motherboard, Chipset, ROM Versions

Urs König has written a very useful short article about these, which may be found at http://www.sinclairql.net/build_standards.html , where you can see pictures of various QL versions and so on. In case of difficulty, a plain text copy can be found here (4K).


capsled.zip - A series of scans of a circuit diagram, instructions and a piece of code to allow a CAPS LOCK indicator LED to be added to a QL. (Q-View) (2MB)
capsled.pdf - Cristian from QL Forum has kindly assembled the scanned documents in the above zip file into a single PDF and done a bit of work to improve the quality fo the scans too. (1.2MB)


Circuits_SQBoard.zip - Circuits. A selection of text files showing most of the pin out connections of the QL & SuperQboard. (14K)

Connor Hard Disks

ConnorHDDSpec.zip - Connor Hard Drive Specs. A text file detailing the specifications of over 35 Connor IDE hard disks. (7K)

CST Q-DISC Circuit Diagram

CST_Schematic.jpg - A handwritten circuit diagram of a CST Q-Disc floppy disc interface, based on v1.16 controller card. (Marcel Kilgus) (447K)
CST_schematic2.png - Circuit diagram reverse engineered from a CST Q-disc by a member of QL Forum (72K)

D2Mac Mods

D2MAC.zip - Ferguson BSB/D2MAC Baseband Decoder Modification. A circuit diagram and text file describing how to modify a satellite receiver for extra channels. (Paul Donald) (5K)


A circuit diagram for a QL 64K EPROM board from z00m, plus a PCB layout diagram from a QL Forum member in Italy.
epromboard.zip (500K)

Expanding Your QL

A two part article about expanding your QL system. Looks at hardware, software and operating systems.
expand.zip (43K)

Expansion Slot and ROM Port Connections

Scanned from QL user guide, these are here as a reference for anyone wishing to construct interfaces to connect to one of these slots.
QL expansion slot (178K JPG file)
QL ROM slot (98K JPG file)

Fast Serial Board

Terry Harman's fast serial board project, allowing speeds of at least 115,200 baud, with plotter files for pcb, GAL 20v8 prog logic etc. The files are HPGL Plotter with .3mm pen plot size x1 and HP PCL laser or Deskjet.
serpcb.zip (129K)
serpcl.zip (88K)
serplot.zip (122K)

HAL (IC38) Chip

A document with equations and JEDEC for the HAL chip in QL (based on issue 5.3 and 6), from information by Robert Klein in the document QL_clones_hardware.pdf below, with small modification by Marcel Kilgus (fixed pin names)  and JEDEC listing from Miroslav Werner, originally published on Sinclair QL For Everyone Facebook Group.
HALic38.txt (6K)

Hard Disk Info

Hard_Disk_Info.zip - Hard Disk Info. A collection of ASCII files giving details of 37 Hard Disks.  Giving details of Heads, Cylinders, Tracks Etc. (27K)

Ian Burkinshaw Hardware Articles

Hardware based projects written by Ian Burkinshaw for QL Today magazine. Ian's articles have their own page - click here.

Interfaces Guide

An article from IQLR magazine by the late Denis Briggs, listing most of the early QL disk interfaces and other cards, complete with simple diagrams to aid identification. The diagrams are PIC files to go with the QL versions of the document.
dbhw.zip (90K)
Alternatively, here is a PDF file version on the document:
intfaces.pdf (596K) [23/11/18]

Internal RAM Expansion

Eagle and WinCUPL files from Phill Harvey-Smith for an internal RAM expansion board for QL. This was originally released via QL Forum in 2014. Phill wrote about this at the time: "There is a layer called 'drill_aid' if you are making the board by hand etching and drilling manually, you should print this layer out when making the masks for the top and bottom etches as it makes locating the drill correctly for drilling the larger holes much easier. You also might want to put a top and bottom layer polygon over the board so you only etch the copper either side of the tracks, you'll probably want to use an isolate setting on this of 24mils, the uploaded board doesn't have this as I normally put multiple boards on a single Eurocard sized board before etching so as to better utilize the board I have a script that draws the eurocard and polygons as needed. You may also need to load the RAM.dru (design rules) or the pads on the CPU may end up being too big. The CPU holes are designed to accommodate turned pins like the ones from sockets pushed out and fitted individually."
InternalRam-mk1.10.zip (59K) [11/02/2020]


How to connect a switched joystick such as an Atari switched joystick to the CTL ports of the QL.
joystick.zip (1K)

Joystick and Serial port connectors. A diagram showing how to recognise UK QL joystick (type 630W left handed, W-polarisation) plugs and UK QL serial port (type 631W right handed, W-polarisation) plugs and pin numberings.
joystickandserialplugtypes.jpg (81K)
Further details on the various BT-style type 600 connectors and their use on QL and ZX Spectrum available at https://zxnet.co.uk/spectrum/btconnectors/

Keith Mitchell Hardware Documents

A series of ASCII files drawn up by Keith as he has serviced some QL add-ons over the years. All should be viewable on an 80 column screen as they are basically plain text files.
hw.zip (13K)

Also, basically the same documents merged into one document, but with a little bit of extra information
hw2.doc - Word .doc file (74K)
hw2.pdf - PDF file (122K)


Here is a diagram of the keyboard connection for a QL, based on the diagram in Fig. 4.2 of the QL Service Manual, which says "The configuration is basically an 8x8 matrix with particla extra diode isolation." The improved diagram is by Lee Privett:

Two articles about tinkering with the QL keyboard may be found here:
Using an Arduino to connect a QL keyboard to a PC via USB
Putting a Raspberry Pi into a QL case


A diagram (93K) from Cristian on QL Forum, showing how to re-attach the LED (Light Emitting Diodes) wires inside the QL. JPEG image.

Medic Board Circuit Diagrams

Circuit diagram, in two parts, of the Medic QL expansion boards.


Some notes on QL microdrives, from Tobias Fröschle
Microdrives.pdf (192K)

High Speed Modems

highspeedmodems.zip - An article from 1992 which discusses high speed dial-up modems, including the 9600 and 14400 bps systems emerging at that time. (11K)

Mouse Project

Picture of a GC QLMouseGianni Carugno has kindly released this QL mouse project. This project allows a PS/2 mouse to be connected to the CTL ports on a QL and emulates cursor key presses. The zip file includes a number of PDF files with circuit diagrams, PCB layouts, parts list, adaptor lead details and firmware. Power can be supplied either via a low power PSU or from the QL via the external ROM port.
gc_qlmouse.zip (124K)


QL network protocols. Notes on the QL network and timings, both on standard BBQL and with Toolkit 2.
QL_Network_Protocols.pdf (84K)

Parallel Port

Picture of the parallel port interfaceA user on QL Forum came across a rare parallel printer interface for a QL, which connects to the QL EPROM slot. We believe it may have been released by Adman Services. It has a small onboard EPROM.

For posterity, a zip file has been prepared with the contents of the ROM and the GAL, plus the Eagle 6.x design files for the traced circuit.

par_printer.zip (35K)

Peripheral ROMs

A short extract from Andy Pennell's QDOS Companion book, which documents the ROM header code for an expansion card ROM, and how to work around the limitation that older QLs (up to and including QDOS v1.13/version JM) can normally only recognise one peripheral card with an on-board ROM. A short piece of assembler code is included to help explain how to correct or work around this. May be particularly useful for those wishing to build a peripheral expansion backplane unit, for example.
Peripheral ROMs (PDF) (192K)

QEP III Service Manual

Ian Burkinshaw has produced a Service Manual to help with repairing QEP III Eprom Programmer boards. Includes circuit diagrams in the PDF file. The spreadsheet (Excel format) contains test resuls to aid fault finding.
QEP3 Service Manual ver2.pdf (1.3MB) - QEPIII service manual PDF file (revised 21/03/16]
QEP3%20test%20sheet.xls (57KB) - Test results spreadsheet

QL Circuit Diagram

Circuit diagrams of the QL issue 5 and issue 6 boards. Scanned from QL Service Manual. The originals were poor quality, so I scanned these at high resolution (600dpi) to try to preserve quality as best as I could, but this has resulted in very large approximately A3 sized scans.
QL block diagram (581K, PNG file)
Issue 5 Board Circuit Diagram (3.8MB JPG file)
Issue 6 Board Circuit Diagram (3.3MB JPG file)

Jörg Kramer has kindly scanned a higher quality version of some of the QL circuit diagrams. He supplied them as TIF files, but due to the size I converted them to somewhat smaller colour PNG files without loss of quality, and to even smaller (slight loss of quality) black and white files:
QL Circuit Diagram Issue 5 colour (9MB)
QL Circuit Diagram Issue 5 mono (0.5MB)
QL Circuit Diagram Issue 6 colour (9MB)
QL Circuit Diagram Issue 6 mono (0.5MB)
QL Block Diagram colour (2.8MB)
QL Block Diagram mono (99KB)
QL PCB Component Layout Issue 5 colour (3.5MB)
QL PCB Component Layout Issue 5 mono (147KB)
QL PCB Component Layout Issue 6 colour (3.5MB)
QL PCB Component Layout Issue 6 mono (135KB)

I've been sent a couple of revised and updated circuit diagrams of the issue 5 and 6 QL boards, with some corrections as indicated in the QLschem.txt file below. I very much hope that these diagrams are correct - if anyone has feedback on them I'll pass on the comments to the author in case these need updating for any reason. Thanks to Marcel Kilgus for an additional update pertaining to the ZX8302 to the issue 6 schematic - see QLschem.txt for details. (David Westbury)
QLschem.txt (1K) - described the changes made in these diagrams.
QLissue5.pdf (74K) - revised circuit diagram for issue 5 QL PCB (PDF file). [10/03/14]
QLissue6.pdf (111K) - revised circuit diagram for issue 6 QL PCB (PDF file). [17/08/18]

QL Clones Hardware

Some notes on the hardware in various QL-type systems and add-ons.
QL_clones_hardware.pdf (91K)

QL Peripherals

Schematics and layout diagrams of some common QL peripheral cards, including Miracle Expandaram, Miracle ROM Port Hard Disk Interface, Miracle Midi V3 and a UK2000 QL PSU (power supply unit - 2 variations)). Zipped PDF files. Hopefully useful for anyone interested in how these devices work, or perhaps for someone trying to repair one of them.
QLperip.zip (57K)

QL Power Supply

A diagram showing the pinouts and voltage label of the UK and USA QL power supply unit, to help anyone wishing to create a replacement power supply.
QL Power Supply (.PNG file - 56K)
Thanks to Alberto M. Franchi on the "Sinclair QL For Everyone" group on Facebook, here are circuit diagrams of the two main types of QL power supplies, both providing the 9v/16V feeds, but to build one you would need to find the required transformers with multiple secondary outputs, and the QL power plug can be impossible to buy as well now.
psu1.jpg (82K) - Regulation directly through thyristor.
psu2.jpg (81K) - Regulation using transformer winding.


This Disk contains Dirk Steinkopf's PD Hard Disk Interface and Software for the Sinclair QL. The Hard Disk system components are as follows:
1. A Hard Disk (not supplied) any drive that can be connected to an OMTI or WD controller i e MFM or RILL Drive.
2. An OMTI-5520, WD-1 002A-WX1 or ST11 R Controller (not supplied).
3. A circuit to connect the Controller to the QL bus (diagram supplied).
4. The driver Software which is the Interface to QDOS (supplied on the Disk.
QLHD.zip (274K)

VGA Monitors With QL

Normally, you cannot connect a QL video output to VGA monitors as the QL video signal is not compatible. However, with a couple of adaptor boards, as described in this article, it is possible to connect a QL to a VGA monitor and in most cases get the full 85 characters per line without the usual loss of a couple of characters at the edges of the Monitor Mode display of the QL.
ql2vga.doc Word doc version of QL to VGA monitor article (1.07MB)
ql2vga.pdf PDF file version of QL to VGA Monitor article (239K)

The above article refers to a device called the Simple Video Scalar from JS Technology Ltd. Here is an article about the device from Dr. John Sim of JS Technology Ltd, originally published in Quanta magazine, about the device:
SimpleVideoScalar.pdf (99K) - PDF format.

Marcel Kilgus (he of QPC2 and QPCprint fame) has announced in 2019 that he is working on a QL to VGA display adaptor board. You can read about his work and progress on the device on his blog at https://www.kilgus.net/blog/

QL Video

Two articles about the QL video system. The first is a PDF file from Marcel Flipse which shows how to make a little circuit board which inverts the Csync pin video signal. This allows the QL to be connected to CGA monitors, which expect an active-high signal (QL Csync pin normally gives out an active-low signal). The second article (from Bob Gilder) explains how to use an IBM CGA monitor with a QL.
cga.zip (184K)

QL video monitor connection. A scan of the diagram from the QL manual for reference with pinouts for a QL monitor connection.
monitor connections.jpg (150K JPG file)

SCART Video Connection

Article from QL Today by Richard Cooke showing how to connect QL video to a Scart input TV. Details for both RGB and composite video. Shows how to connect suitable value resistors in line with the colour signals to ensure correct voltages etc. along with the calculations involved.
scart.zip (29K)

Serial Ports Connections

Serial ports are a very useful means of interconnection between computers, but wiring cables for them can be a tricky experience! This article, written with advice from Tony Firshman, shows how easy it is to connect up the various types of serial ports you are likely to encounter. It may be useful if you wish to try to make up cables for use with the Sernet serial networking software for example. An article from QL Today magazine. The second article is also about making cables for serial file transfers between QL and PC. Covers making cables for QL connectors and PC serial ports which use 9-pi and 25-pin D connectors. The diagrams are in .GIF format.

serials.zip (124K)
German QL Serial Ports (2K)

Picture of German QL serial ports
Picture of German QL serial port sockets

Sermouse - SER2 Adaptor

Thanks to Cristian on QL Forum, here's a JPEG diagram (130K) of the wiring for a UK 6-pin SER2 to 9-pin Sermouse adaptor cable.

SuperQBoard Modifications

A set of text documents from Keith Mitchell about upgrading a SuperQBoard interface: the mouse interface, PALs and ROM upgrade and piggy back memory upgrade.
sqbmods.zip (5K)

A pair of circuit diagrams of the SuperQBoard interface from Marcel Kilgus. The first is for a DD disk drive version, the second for a HD disk upgrade. Both are .png file graphics.
ql-flp.png (158K) The DD version.
ql-flp-hd.png (165K) The HD version

Marcel Kilgus has written an article on his blog, where he describes an old very customised QL of his, and written about the modified SuperQBoard and an Eprommer II board. The article includes circuit diagrams, design and software - ROM images and GAL files. https://www.kilgus.net/2020/09/05/hardware-from-my-past/

Surge Protection

Surge_Protection.zip - Surge Protection. Notes on building simple surge protectors for computers and other electrical equipment. A USA file, so refers to 110 volt electrical systems. (Chemical Kidd)

UK QL Serial Ports

An article by H.P.Recktenwald about the U.K. QL serial ports.
ukqlser.zip (7K)

Ulrich Rosowski Interface PCB Photos

A document with photos of the PCBs of hardware from Ulrich Rosowski. No documentation, other than what can be seen etched onto the PCBs. Includes hardware such as the U+5 expansion backplane, Mega-RAM, HD-V2 (hard disk bus interface), Internal ROM expansion card, keyboard interface. Includes some photos of QIMI PCBs too. Further photos may be seen on QL Forum.
ql-platinen.pdf (12M)

WD150XT Text

WD150XT_Text.zip - WD150XT. Information and diagram for use with the Western Digital XT Intelligent Storage Peripherals interface card. For IBM XT or compatibles computers. (7K)

What Hardware

Two packages showing how you can read system information to determine what type of QL hardware and operating system your software is running on.

1. Which Machine Am I Running On?
More recent versions of our favourite operating systems have been ported to runon various processors and platforms. This article from QL Today documents system variables and language extensions which will help software to identify which platform it's running on, e.g. so it can check for certain hardware facilities and take advantage of them. The article has been slightly amended from the one published in QL Today (QLay hardware code details). Note also that since this article was written, QPC2 no longer pretends to be a 68010 as it now pretends to be a 68020 since it supports new instructions from that processor.
machine.zip (8K)

2. A package by J.D.Mitchell to allow a degree of machine interrogation via simple BASIC procedures, capable of running on most if not all systems.
whathw.zip (5K)


A document in three formats (DOC, ODT and PDF) about the ZX8301 chip in the QL. Compiled by Derek Stewart from postings by Nasta on this subject on QL Forum.
8301.zip (1MB) [22/10/18]

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