Amstrad NC100 Troubleshooting Guide
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Most faults reported on the Amstrad NC100 are power faults: flat or leaking AA cells, a dead lithium backup cell, the wrong adaptor, or a software lock-up that needs a reset. Amstrad published user-level instructions; the board-level detail here comes from Hans-Jürgen Böhling's surgical guide and from the hardware chapter of Robin and Chris Nixon's Advanced User Guide.[1][2][3] Procedures are in the Amstrad NC100 Maintenance Guide.
How the power circuit works
[edit | edit source]Böhling's power supply diagram shows the 6 V DC adaptor input passing through fuse F301, and the four AA cells and the lithium cell feeding a DC/DC converter and battery-level detector. The converter produces +6 V, +5 V, a lithium-backed 5 V line (5VBK) for the RAM and clock, and −15 V for the LCD. A push switch, S301, sets a flip-flop (IC313A) that switches the converter on; the custom chip's POFF line resets it, and the clock's alarm output is wired to the same set input.[2]
The battery-level signals go to the custom chip and can be read at I/O port &A0. The two sources give different thresholds:
| Signal | Böhling's power diagram | Nixon, port &A0 |
|---|---|---|
| Main cells low | BD1: four AA below 4.2 V; BVD2: below 3.2 V | Bit 3: below 3.2 V, though "tests show this may be nearer to 4.2 volts in practice" |
| Lithium cell low | BD2: below 2.3 V | Bit 2: below 2.7 V |
| Mains adaptor | – | Bit 5: adaptor below 4 V |
| Memory card battery | – | Bit 4: 1 if the card battery is good |
Sources: Böhling's diagram[2] and Nixon's port description.[3]
Power faults
[edit | edit source]| Symptom | Probable cause | Action |
|---|---|---|
| Dead on batteries and on the adaptor | Lock-up, internal fuse F301, the S301/IC313A switch-on circuit | Try the reset below. Then measure the AA cells and the adaptor output, and check F301 with the case open. Tim Surtell's site gives the NC100's surface-mount fuse as 6 V 0.8 A and says a wrong-voltage or reversed adaptor can blow it |
| Works on the adaptor, dead on batteries | Flat or reversed cells, corroded contacts | Fit fresh LR6 cells the right way round; clean the contacts |
| Works on batteries, dead on the adaptor | Adaptor, lead, adaptor socket | Use only the supplied adaptor (6 V DC, 300 mA, unregulated). Measure its output and polarity and inspect the lead where it enters the plug and the connector |
| "battery is low, please switch off and replace battery" | Main cells low | Replace the four AA cells |
| "Lithium battery is low" | Backup cell low | Replace the CR2032 with good AA cells fitted or the adaptor connected |
| Memory lost after a battery change | Dead or missing lithium cell, or all sources removed together | Replace the CR2032; restore files from a card or another computer |
| Batteries run down quickly | Automatic power-off set to 0, serial port use, NiCd cells | Set the power-off delay to 1 to 5 minutes; use the adaptor for serial transfers |
The messages and remedies are Amstrad's;[1] the fuse rating and adaptor details come from Tim Surtell's NC users' site.[4] NiCd cells give about 5 hours against 35 to 40 hours for alkaline cells, so a short run time on rechargeables is not a fault.[1]
Lock-ups and reset
[edit | edit source]The documented reset erases everything in the Notepad's memory, including the password, but leaves the contents of a memory card alone: switch off, then hold down Function, Stop and the ←Del key on the right while switching on. A long beep confirms the reset. Sticky shift cannot be used for it.[1]
Nixon reports two further cases. A crash can leave the machine returning to the menu but blanking the screen when BASIC is entered; switching off and on again and pressing Function and B once more may clear it. Some crashes lock the machine so that no key combination works. The cure is to remove the four AA cells, the adaptor lead, the lithium cell and any memory card, press the power key repeatedly for a minute or two to drain the remaining charge, then refit everything. This erases all data in the machine.[3]
Display
[edit | edit source]| Symptom | Probable cause | Action |
|---|---|---|
| Screen blank or faint, machine beeps at switch-on | Brightness control | Adjust the control on the right-hand edge |
| Blank screen after the case has been opened | Display flat cable not seated | Reseat the cable in its socket on the main board |
| Blank or missing display on an older machine | Failed ribbon cable between the main board and the display board | Owners have replaced it with Farnell part 145-5423 |
| Blank screen, machine otherwise working | LCD supply | Böhling's diagram shows a −15 V supply for the LCD from the DC/DC converter; check for it at the display connector |
Sources: Amstrad's setting-up pages,[1] Böhling's guide[2] and the NC users' site.[4] The site's blank-screen checklist, taken from the NC200 manual, also says to check the batteries, to unplug the adaptor when running on batteries, and to try the reset.[4] The NC100 display is not backlit.[5]
Memory cards
[edit | edit source]- Only SRAM cards work; flash cards do not.[2]
- A new card must be formatted from the stored-documents menu.[1]
- The card's battery state and write-protect switch are reported to the Notepad through port &A0. Check both when a card will not save or loses its contents.[3]
Serial and printer ports
[edit | edit source]The serial port uses a µPD71051 UART (IC308) and a µPD4711 line driver (IC309); the parallel port is driven by the custom chip.[2] If a serial transfer produces rubbish, Amstrad's manual points to mismatched baud rate, data bits, stop bits or parity.[1] One owner on the NC users' site could only make his NC100 transfer reliably at 9600 baud using XModem and the mains adaptor.[4] The printer can be set to the serial or the parallel port in the printer settings.[1]
Related pages
[edit | edit source]- Amstrad NC100 · Amstrad NC100 Maintenance Guide
- Amstrad NC150 Troubleshooting Guide
- Battery Explosion, Capacitor or Corrosion Damage · Battery Refurbishment
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Amstrad plc, Amstrad Notepad Computer user manual. Hosted as File:Amstrad Notepad Computer User Manual.pdf, described at Amstrad Notepad Computer User Manual. Setting up pp. 1–2; mains adaptor p. 4; powering the Notepad p. 43; automatic power off p. 44; memory cards p. 47; resetting p. 60; serial transfers p. 109.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Hans-Jürgen Böhling, A Surgical Guide To The Amstrad Notepad Computer. Community document, hosted as File:Amstrad NC100 Surgical Guide.pdf, described at Amstrad NC100 Surgical Guide. IC table, power supply block diagram, opening the case, PCMCIA slot.
- ↑ 3.0 3.1 3.2 3.3 Robin Nixon and Chris Nixon, The Amstrad Notepad Advanced User Guide (Sigma Press, 1993), pp. 155–156 (port &A0, memory card and battery status) and pp. 187–188 (reset and lock-up recovery). Scan at archive.org. Retrieved 2026-10-02.
- ↑ 4.0 4.1 4.2 4.3 Tim Surtell, Tim's Amstrad NC Users' Site, "Questions & Answers: Hardware". Retrieved 2026-10-02. Community answers: the blank-screen checklist from the NC200 manual, the internal surface-mount fuse (6 V 0.8 A on the NC100), adaptor rating and polarity, mains lead repair, case cracking, the NC100 display ribbon cable, serial port reliability, memory cards up to 1 MB, and Cliff Lawson on the NC150's Ranger disk hook.
- ↑ Wikipedia, "Amstrad NC100". Retrieved 2026-10-02. The unlit 80 × 8 display.