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| {{Infobox computer
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| | name = Sinclair ZX80
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| | image = [[File:ZX80.jpg|250px]]
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| | caption = A fully–assembled Sinclair ZX80
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| | manufacturer = Science of Cambridge Ltd (later Sinclair Research Ltd)
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| | type = Home computer / hobbyist kit
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| | release date = 29 January 1980
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| | discontinued = March 1981 (superseded by ZX81)
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| | price = £79 .95 kit / £99 .95 ready-built (≈US$199/249 in 1980)
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| | cpu = Zilog Z80A-compatible (NEC µPD780C-1) @ 3.25 MHz
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| | memory = 1 KB static RAM on-board (expandable to 16 KB, 48 KB with mods)
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| | storage = External cassette tape (300 baud, EAR/MIC jacks)
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| | display = Monochrome RF to TV – 32 × 24 text or 64 × 48 block-graphics
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| | sound = None (no audio hardware)
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| | dimensions = 195 mm × 175 mm × 50 mm (7.7 ″ × 6.9 ″ × 2.0 ″)
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| | weight = ≈ 340 g (0.75 lb)
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| | os = 4 KB Sinclair Integer BASIC in ROM
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| | predecessor = [[Science of Cambridge MK14]]
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| | successor = [[Sinclair ZX81]]
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| | codename = “ZX80 project”
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| | model = ZX80
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| }}
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| The '''Sinclair ZX80''' is an 8-bit home computer marketed by Sir Clive Sinclair’s '''Science of Cambridge''' (soon renamed '''Sinclair Research''') as ''“the first personal computer for under one hundred pounds.”'' Released in January 1980, it ignited the UK micro-boom and sold about 100 000 units worldwide despite numerous limitations – most famously its blanking video that disappears while BASIC is running code.
| | = Sinclair ZX80 General Maintenance = |
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| The '''ZX80''' arrived in February 1980—just months before the BBC Micro project was even conceived—and became the '''first consumer microcomputer to retail for under £100''' in the United Kingdom.<ref>Mail-order advert, ''Practical Computing'', March 1980. | | The Sinclair ZX80 is a classic home computer that requires regular maintenance to ensure optimal performance and longevity. This guide provides detailed procedures for cleaning, troubleshooting, and maintaining your ZX80. |
| * '''Launch prices''' (1980): '''£79.95''' in kit form, '''£99.95''' fully assembled (plus £4 P&P).
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| * Sinclair’s glossy national-press adverts boasted “The computer you can afford to own” and invited readers to “own a real computer for less than the price of a colour TV.”
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| * Production was handled by Timex’s Scottish plant in Dundee; the first 10 000 boards were delivered in six weeks.
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| * '''Estimated lifetime sales:''' contemporary interviews with Clive Sinclair quote “50–70 000 kits” and around “30 000 ready-built” units, giving an aggregate of '''≈ 100 000 ZX80s worldwide''' before the ZX81 superseded it in March 1981.
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| == 🧠 Architecture == | | == Table of Contents == |
| * '''CPU''' – Z80A-class microprocessor clocked at '''3.25 MHz''' (half the UK colour-burst for simple TV timing). | | * [[#Cleaning the ZX80|Cleaning the ZX80]] |
| * '''ROM''' – 4 KB mask ROM containing Sinclair Integer BASIC, line-editor and I/O routines. | | * [[#Internal Inspection|Internal Inspection]] |
| * '''RAM''' – 1 KB of 2114 static RAM; addressable to 48 KB via the rear expansion bus (commonly 16 KB DRAM pack). | | * [[#Troubleshooting Common Issues|Troubleshooting Common Issues]] |
| * '''Logic''' – Built entirely from 18 inexpensive 74-series TTL ICs; no custom chips – video, keyboard scan and cassette I/O are all done in firmware. | | * [[#Diagnostics|Diagnostics]] |
| | * [[#Preventive Maintenance|Preventive Maintenance]] |
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| === Video generation === | | == Cleaning the ZX80 == |
| The Z80 itself bit-bangs UHF video: during the '''FAST''' display loop it outputs a sync pulse then immediately fetches the next character row from RAM, interleaving code and picture. When the CPU is diverted to BASIC interpretation the timing breaks, so the TV loses sync – producing the ZX80’s trademark flicker. (The later ZX81 added a SLOW mode with hardware assistance to cure this.)
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| == 💾 Storage ==
| | Regular cleaning is essential to keep your ZX80 in good working condition. Follow these steps to clean the exterior and interior of the device. |
| Load / SAVE uses the '''300 baud Kansas City Standard''' with simple square waves on 3.5 mm EAR/MIC sockets. Program listings average ~4 seconds per KB.
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| == 🔌 I/O and Expansion == | | === Materials Needed === |
| * '''Edge connector (44-way)''' – exposes full Z80 bus, power and video lines. | | * Soft, lint-free cloth |
| * '''9 V DC input''' – un-regulated (internally regulated to 5 V). | | * Isopropyl alcohol (70% or higher) |
| * '''RF modulator''' – channel 36 PAL TV. | | * Small brush (e.g., paintbrush) |
| Commercial add-ons included:
| | * Compressed air canister |
| : ''1–3 KB SRAM packs, 16 KB DRAM pack''
| | * Screwdriver (Phillips) |
| : ''ZX Printer, joystick adapters, floppy-drive interfaces, composite video mods''.
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| == 🔧 Known PCB Revisions & Errata == | | === Step-by-Step Cleaning Procedure === |
| {| class="wikitable styled-table" style="width:70%; text-align:center;" | | {| class="styled-table" |
| |+'''ZX80 Logic-Board Issues'''
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| ! Issue !! Visible Clues !! Key Fixes / Changes
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| |- | | |- |
| | '''Issue 1''' (Feb 1980) || “ZX80 Issue 1” silkscreen; no solder mask between edge pads. || • Missing pull-ups on IC12 (74LS05) video drivers caused weak sync on some TVs.
| | ! Step !! Description |
| • Regulator IC5 runs hot—Sinclair added stick-on heatsink in later batches.
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| |- | | |- |
| | '''Issue 2''' (late 1980) || Added green solder mask; extra wire-link near IC12. || • 4× 1 kΩ SIL resistor pack RP1 installed for stronger TTL drive. | | | 1 || Unplug the ZX80 from the power source and disconnect all peripherals. |
| • Board edge widened 1 mm to fit Timex card guides.
| | |- |
| | | 2 || Use the soft cloth dampened with isopropyl alcohol to wipe the exterior surfaces, including the keyboard and casing. |
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| | | 3 || For stubborn dirt, use a small brush to gently scrub the affected areas. |
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| | | 4 || Use the compressed air canister to blow out any dust or debris from the ventilation grilles and keyboard. |
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| | | 5 || Open the case by removing the screws on the back panel using the screwdriver. |
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| | | 6 || Carefully lift the top cover and set it aside. Use the compressed air to clean the interior components, avoiding direct contact with sensitive parts. |
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| | | 7 || Inspect the internal connections and cables for any signs of wear or damage. |
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| | | 8 || Reassemble the ZX80 by reversing the disassembly steps and ensure all screws are securely fastened. |
| |} | | |} |
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| == 🛠️ General Maintenance == | | == Internal Inspection == |
| {| class="wikitable styled-table" style="width:70%; text-align:center;" | | |
| ! Issue !! Cause !! Remedy
| | Performing an internal inspection can help identify potential issues before they become serious problems. |
| | |
| | === Step-by-Step Internal Inspection Procedure === |
| | {| class="styled-table" |
| |- | | |- |
| | Unstable picture / snow || Ageing electrolytic C5 (47 µF) on video rail || Replace with low-ESR 105 °C part
| | ! Step !! Description |
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| | Reboots when touched || Loose 7805 regulator tab shorts to case || Insulate tab / fit TO-220 spacer | | | 1 || Ensure the ZX80 is unplugged and opened as described in the cleaning procedure. |
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| | RAM pack “wobble” resets || Leverage on edge bus ⇒ poor contact || Fit retention bracket or right-angle header | | | 2 || Visually inspect the circuit board for any signs of corrosion, burnt components, or loose connections. |
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| | Overheating || No ventilation slots (black “stripes” are cosmetic) || Drill discreet vents or run uncased board | | | 3 || Check the power supply connections for secure fit and any signs of wear. |
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| | | 4 || Inspect the RAM chips for proper seating and any visible damage. |
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| | | 5 || Look for any bulging or leaking capacitors on the board. |
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| | | 6 || If any issues are found, consider replacing the affected components or consulting a professional technician. |
| |} | | |} |
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| Full recapping, regulator heatsinking and replacement of the brittle membrane keyboard are popular reliability upgrades.
| | == Troubleshooting Common Issues == |
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| == 📜 Schematic & PCB == | | If your ZX80 is not functioning properly, follow these troubleshooting steps to identify and resolve common issues. |
| The complete single-layer PCB schematic is freely available
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| {| class="wikitable" | | === Common Issues and Solutions === |
| |+ | | {| class="styled-table" |
| ! [[File:ZX80_Schematic.png|thumb|center|500px|Sinclair ZX80 circuit diagram]] | | |- |
| ! [[File:ZX80_PCB_Top.jpg|thumb|center|260px|Original Issue 1 board – note hand-drawn track work]] | | ! Issue !! Symptoms !! Solution |
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| | | No Power || No lights or sounds when powered on || Check power supply and connections. Replace if faulty. |
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| | | Display Issues || Distorted or no display on screen || Check video cable connections. Inspect the video output circuitry. |
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| | | Keyboard Malfunction || Keys not responding || Clean the keyboard contacts and check for loose connections. |
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| | | Overheating || Excessive heat from the unit || Ensure proper ventilation and check for dust buildup inside. |
| | |} |
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| | == Diagnostics == |
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| | To further diagnose issues with your ZX80, use the following methods. |
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| | === Basic Diagnostic Tests === |
| | {| class="styled-table" |
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| | ! Test !! Description |
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| | | 1 || Power On Self Test (POST) - Upon powering on, listen for beeps or observe LED indicators. Any irregularities may indicate hardware issues. |
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| | | 2 || RAM Test - Use built-in commands to test RAM functionality. If errors are reported, consider replacing RAM chips. |
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| | | 3 || Keyboard Test - Press each key to ensure it responds correctly. If any keys fail, inspect and clean the keyboard. |
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| | | 4 || Display Test - Connect to a known working monitor to rule out display issues. If the problem persists, inspect the video output. |
| | |} |
| | |
| | == Preventive Maintenance == |
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| | To prolong the life of your ZX80, follow these preventive maintenance tips. |
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| | === Preventive Maintenance Tips === |
| | {| class="styled-table" |
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| | ! Tip !! Description |
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| | | 1 || Keep the ZX80 in a cool, dry environment to prevent moisture damage. |
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| | | 2 || Use a surge protector to safeguard against power surges. |
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| | | 3 || Regularly clean the exterior and interior as outlined in the cleaning section. |
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| | | 4 || Store the ZX80 in a protective case when not in use to prevent dust accumulation. |
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| | | 5 || Periodically check and replace any worn cables or connectors. |
| |} | | |} |
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| == 🔧 Common Modifications ==
| | By following this maintenance guide, you can ensure that your Sinclair ZX80 remains in excellent working condition for years to come. |
| * '''8 KB ZX81 ROM upgrade''' – drops-in to give floating-point BASIC, SAVE/LOAD VERIFY and better editing (still no SLOW mode).
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| * '''
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