|
|
| (8 intermediate revisions by the same user not shown) |
| Line 1: |
Line 1: |
| | The Sinclair ZX80 is a classic home computer, and with careful maintenance, it can remain reliable for decades. This guide covers essential care, preventive steps, and troubleshooting for all ZX80 board revisions. |
| | '''Always observe ESD (Electrostatic Discharge) precautions''' when handling the PCB or components—use a grounded wrist strap and work on an antistatic mat. |
| | Regular maintenance intervals: |
| | * '''Visual inspection:''' Every 12 months |
| | * '''Capacitor check:''' Every 2–3 years |
| | * '''Full electrical test:''' Every 5 years or after storage |
| | |
| <templatestyles src="Template:StyledTable/styles.css" /> | | <templatestyles src="Template:StyledTable/styles.css" /> |
| {{Infobox computer
| | [[File:ZX80_PCB_Top.jpg|thumb|right|300px|Sinclair ZX80 Mainboard (Issue 2)]] |
| | name = Sinclair ZX80
| |
| | image = [[File:ZX80.jpg|250px]]
| |
| | caption = A fully–assembled Sinclair ZX80 | |
| | manufacturer = Science of Cambridge Ltd (later Sinclair Research Ltd)
| |
| | type = Home computer / hobbyist kit
| |
| | release date = 29 January 1980
| |
| | discontinued = March 1981 (superseded by ZX81)
| |
| | price = £79 .95 kit / £99 .95 ready-built (≈US$199/249 in 1980)
| |
| | cpu = Zilog Z80A-compatible (NEC µPD780C-1) @ 3.25 MHz
| |
| | memory = 1 KB static RAM on-board (expandable to 16 KB, 48 KB with mods)
| |
| | storage = External cassette tape (300 baud, EAR/MIC jacks)
| |
| | display = Monochrome RF to TV – 32 × 24 text or 64 × 48 block-graphics
| |
| | sound = None (no audio hardware)
| |
| | dimensions = 195 mm × 175 mm × 50 mm (7.7 ″ × 6.9 ″ × 2.0 ″)
| |
| | weight = ≈ 340 g (0.75 lb)
| |
| | os = 4 KB Sinclair Integer BASIC in ROM
| |
| | predecessor = [[Science of Cambridge MK14]]
| |
| | successor = [[Sinclair ZX81]]
| |
| | codename = “ZX80 project”
| |
| | model = ZX80
| |
| }}
| |
|
| |
|
| 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.
| | == Board Revisions == |
| | {| class="wikitable styledtable" |
| | ! Revision !! PCB Markings !! Notable Differences !! Common Issues |
| | |- |
| | | Issue 1 || "ZX80 ISSUE ONE" silk || Early production, hand-wired mods || Poor video sync, regulator overheating |
| | |- |
| | | Issue 2 || "ZX80 ISSUE TWO" silk || Improved video, revised regulator layout || Keyboard connector wear, RAM instability |
| | |} |
|
| |
|
| 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. | | == Power Supply & Regulator Care == |
| * '''Launch prices''' (1980): '''£79.95''' in kit form, '''£99.95''' fully assembled (plus £4 P&P). | | The ZX80 uses a simple linear power supply: |
| * 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.” | | * '''PSU Part:''' Sinclair 9V DC Adapter (center negative) |
| * Production was handled by Timex’s Scottish plant in Dundee; the first 10 000 boards were delivered in six weeks. | | * '''Specs:''' 9V DC, 700–1000mA, 2.1mm barrel |
| * '''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. | | * '''On-board Regulator:''' 7805 (IC3) 5V linear |
| | * '''Common Failure Modes:''' |
| | ** PSU cable splits or shorts |
| | ** 7805 overheating or output drift |
| | ** Capacitor (C4, C5) leakage or bulging |
|
| |
|
| == 🧠 Architecture ==
| | '''On-board Capacitor Designators:''' |
| * '''CPU''' – Z80A-class microprocessor clocked at '''3.25 MHz''' (half the UK colour-burst for simple TV timing).
| | * '''C4, C5:''' Smoothing and decoupling for 7805 |
| * '''ROM''' – 4 KB mask ROM containing Sinclair Integer BASIC, line-editor and I/O routines. | | * '''C1, C2, C3:''' Logic supply filtering |
| * '''RAM''' – 1 KB of 2114 static RAM; addressable to 48 KB via the rear expansion bus (commonly 16 KB DRAM pack). | |
| * '''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.
| |
|
| |
|
| === Video generation === | | == Capacitor Replacement Table == |
| 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.)
| | {| class="wikitable styledtable" |
| | ! Position !! Value !! Voltage !! Notes !! Series/Type |
| | |- |
| | | C1 || 22μF || 16V || Logic rail smoothing || Axial, low ESR |
| | |- |
| | | C2 || 1μF || 16V || Video circuit || Tantalum or electrolytic |
| | |- |
| | | C3 || 0.1μF || 50V || Noise bypass || Ceramic disc |
| | |- |
| | | C4 || 100μF || 16V || 7805 input || Axial, low ESR |
| | |- |
| | | C5 || 100μF || 16V || 7805 output || Axial, low ESR |
| | |} |
|
| |
|
| == 💾 Storage == | | == Voltage & Clock Test Points == |
| 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.
| | {| class="wikitable styledtable" |
| | | ! Test Point !! IC/Pin !! Expected Value (±Tolerance) |
| == 🔌 I/O and Expansion ==
| | |- |
| * '''Edge connector (44-way)''' – exposes full Z80 bus, power and video lines.
| | | 5V Rail || IC3 (7805) Output || 5.00V ±0.15V |
| * '''9 V DC input''' – un-regulated (internally regulated to 5 V).
| | |- |
| * '''RF modulator''' – channel 36 PAL TV.
| | | 9V Input || C4 (+) || 9.0V ±0.5V |
| Commercial add-ons included:
| |
| : ''1–3 KB SRAM packs, 16 KB DRAM pack''
| |
| : ''ZX Printer, joystick adapters, floppy-drive interfaces, composite video mods''.
| |
| | |
| == 🔧 Known PCB Revisions & Errata ==
| |
| {| class="wikitable styled-table" style="width:70%; text-align:center;"
| |
| |+'''ZX80 Logic-Board Issues''' | |
| ! Issue !! Visible Clues !! Key Fixes / Changes
| |
| |- | | |- |
| | '''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. | | | CPU Clock || IC1 (Z80) Pin 6 || 3.25MHz ±0.05MHz |
| • Regulator IC5 runs hot—Sinclair added stick-on heatsink in later batches.
| |
| |- | | |- |
| | '''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. | | | Video Sync || IC5 Pin 3 || 5Vpp square wave |
| • Board edge widened 1 mm to fit Timex card guides.
| |
| |} | | |} |
|
| |
|
| == 🛠️ General Maintenance == | | == Essential Tools == |
| {| class="wikitable styled-table" style="width:70%; text-align:center;" | | * Antistatic wrist strap & mat |
| ! Issue !! Cause !! Remedy | | * Multimeter (with continuity and voltage) |
| | * Oscilloscope (≥10MHz, for clock/video) |
| | * Soldering iron (fine tip, ESD safe) |
| | * Solder sucker or wick |
| | * Small flat and Phillips screwdrivers |
| | * IC extractor |
| | * Fine tweezers |
| | * Isopropyl alcohol & brush (for cleaning) |
| | |
| | == Preventive Maintenance Checklist == |
| | # Power off and unplug the unit. |
| | # Discharge static and open the case. |
| | # Inspect PCB for corrosion, broken traces, or burnt components. |
| | # Check all capacitors for bulging or leakage. |
| | # Verify keyboard membrane and connector for cracks. |
| | # Clean dust and debris with a soft brush. |
| | # Test PSU output voltage before connecting. |
| | # Reseat all socketed ICs gently. |
| | # Inspect solder joints for cracks ("dry joints"). |
| | # Reassemble and test operation. |
| | |
| | == Common Faults & Quick Checks == |
| | {| class="wikitable styledtable" |
| | ! Symptom !! Likely Cause !! Quick Check |
| |- | | |- |
| | Unstable picture / snow || Ageing electrolytic C5 (47 µF) on video rail || Replace with low-ESR 105 °C part | | | No power || PSU or 7805 failure || Measure 9V in, 5V out at IC3 |
| |- | | |- |
| | Reboots when touched || Loose 7805 regulator tab shorts to case || Insulate tab / fit TO-220 spacer | | | No video || C2, IC5, or ULA fault || Scope video out, check C2 |
| |- | | |- |
| | RAM pack “wobble” resets || Leverage on edge bus ⇒ poor contact || Fit retention bracket or right-angle header | | | Keyboard dead || Membrane or connector || Inspect for cracks, reseat |
| |- | | |- |
| | Overheating || No ventilation slots (black “stripes” are cosmetic) || Drill discreet vents or run uncased board | | | Random resets || C1, C4, or RAM || Replace caps, test RAM |
| | |- |
| | | Overheating || 7805 or shorted cap || Check C4/C5, IC3 temp |
| |} | | |} |
|
| |
|
| Full recapping, regulator heatsinking and replacement of the brittle membrane keyboard are popular reliability upgrades.
| | == Troubleshooting Flowcharts == |
| | # '''No Power''' |
| | ## → Check PSU output (9V) |
| | ## → Check 7805 output (5V) |
| | ## → If 5V missing, replace 7805 and C4/C5 |
| | ## → If still dead, inspect PCB for shorts |
|
| |
|
| == 📜 Schematic & PCB ==
| | # '''No Video Output''' |
| The complete single-layer PCB schematic is freely available
| | ## → Confirm 5V present |
| {| class="wikitable"
| | ## → Test C2 and IC5 (video circuit) |
| |+
| | ## → Swap ULA if available |
| ! [[File:ZX80_Schematic.png|thumb|center|500px|Sinclair ZX80 circuit diagram]]
| | ## → Inspect video connector and cable |
| ! [[File:ZX80_PCB_Top.jpg|thumb|center|260px|Original Issue 1 board – note hand-drawn track work]]
| | |
| |}
| | # '''Keyboard Not Responding''' |
| | ## → Inspect membrane for cracks |
| | ## → Clean and reseat connector |
| | ## → Test continuity across matrix |
| | |
| | # '''Random Freezing/Resets''' |
| | ## → Replace C1, C4, C5 |
| | ## → Test RAM ICs |
| | ## → Check for dry joints on IC sockets |
|
| |
|
| == 🔧 Common Modifications ==
| | [[Category:Sinclair Computers]] |
| * '''8 KB ZX81 ROM upgrade''' – drops-in to give floating-point BASIC, SAVE/LOAD VERIFY and better editing (still no SLOW mode).
| |
| * '''
| |
