Sharp MZ-40K Troubleshooting Guide
No fault-finding procedure from Sharp for the Sharp MZ-40K has been found, and no repair reports turned up in the sources consulted. The checks below follow Sharp's schematic diagram and SharpMZ's technical data, section by section.[1][2] Every MZ-40K was built from a kit, so a poor joint or a part fitted the wrong way round is as likely as a failed component.[3]
Symptoms and checks
[edit | edit source]| Symptom | Check | Parts in the path |
|---|---|---|
| Nothing lights | AC at the adaptor plug (about 10.5 to 11 V); the power switch on the volume control; 5 V at the regulator output | Adaptor, S65, 1B4B1, C10, TA78005P, C13 |
| Display dim, flickering or dead digits | 5 V unregulated rail for the LEDs; drive from the transistor arrays; solder joints at each digit | TA1, TA2, TA3, resistor arrays, GL-8P04 digits |
| Clock does not advance or keeps wrong time | AC reaching TR1 through R4, C11, D1 and R5; adaptor is AC, not DC; mains frequency setting | R4, C11, D1, R5, TR1 |
| Processor dead with good 5 V | Crystal oscillator and divider | 3.579545 MHz crystal, C14, C15, IC2, IC4 |
| No sound | Volume control; IC1 supply and input; coupling to the speaker | IC1, C1, C3, C7, C9, C4, speaker |
| A key does nothing | Key switch and its solder joints; keypad wiring to the processor and IC8 | Key switches, IC8 |
| Tune data corrupt or lost while running | RAM chips and their sockets | RAM1, RAM2 |
| Option 1 sensor not detected | Jack, sensor and input transistor; the two option jumpers | JK1 to JK6, TR3 to TR8, C18 to C23 |
Power
[edit | edit source]The adaptor must supply AC. SharpMZ gives 10.5 V AC at up to 700 mA for the European adaptor, and Japanese Wikipedia gives 11 V AC.[2][4] On the board, the 1B4B1 bridge charges C10 (1000 µF 16 V) and the TA78005P regulates 5 V, with C13 (1 µF 50 V) on its output. If the regulated 5 V is missing, check in that order: the jack and switch, the bridge, C10 and the regulator.[1]
Clock
[edit | edit source]The clock counts the mains cycles that arrive through R4, C11, D1 and R5 at TR1, so it keeps time only from an AC supply of the right frequency. Japanese Wikipedia notes that the mains frequency is entered when the clock is set.[1][4] A clock that runs fast or slow by a fixed ratio points to the wrong frequency setting; one that does not advance at all points to the TR1 input path or to a DC supply.[2]
Sound
[edit | edit source]IC1 (LM390 or LM388) drives the speaker through C4 (470 µF 16 V), with C1, C3, C7 and C9 round the amplifier and the 10 kΩ volume control at its input. The volume control also switches the power.[1][2] C4 is the largest capacitor in the audio path; the full list is in the Sharp MZ-40K Capacitor Replacement Guide.
Related pages
[edit | edit source]References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 Sharp Corporation, MZ-40K schematic diagram, reproduced at Diagram MZ-40K, SharpMZ—link(accessed 2026-10-21) Also hosted as File:Sharp MZ-40K schematic diagram.jpg. AC adaptor Z0001 (100 V, 50/60 Hz); power switch S65; bridge 1B4B1; C10 1000 µF 16 V; TA78005P regulator with C12 1000 pF and C13 1 µF 50 V; +5 V unregulated and +5 V outputs; AC through R4 47 kΩ, C11 4.7 µF 25 V, D1 1S1555 and R5 27 kΩ to the base of TR1 (2SC373), whose collector goes to the CPU; crystal 3.579545 MHz in an oscillator built from IC2 gates with C14 0.1 µF and C15 100 pF, feeding IC4; IC3 divider; LED digits driven through the transistor arrays TA1, TA2 and TA3 and resistor arrays RA1 to RA8; keypad of 22 keys wired to the CPU and IC8; IC1 audio amplifier with C1 and C9 4.7 µF 25 V, C3 and C7 22 µF 16 V, C4 470 µF 16 V, 10 kΩ volume control and an 8 Ω speaker (8OP-30BP); RAM1 and RAM2 (X0043PAZZ); Option 1 inputs JK1 to JK6 with TR3 to TR8, DAP601 arrays and C18 to C23 (10 µF 16 V); Option 2 socket.
- ↑ 2.0 2.1 2.2 2.3 2.4 Technical data of the MZ-40K, SharpMZ—link(accessed 2026-10-21) Processor clock 1.7897725 MHz, the 3.579545 MHz crystal divided by 2 by the 7493 (IC4); timer clock 223.722 kHz (divided by 2 by IC4 and by 8 by the 7476, IC3); LEDs multiplexed by the CPU timer; IC1 LM390 or LM388, 400 mW maximum; volume control with combined on-off switch; 10.5 V AC input giving 5 V unregulated for the LEDs, 5 V regulated and 5 V AC for the clock; no DC power supply can be used; two option jumpers for Option 1; four telephone jumpers.
- ↑ The MZ-40K kit– SharpMZ and Richard Cornelius, SharpMZ—link(accessed 2026-10-21) Sold only as a kit; the German manual has 23 pages of assembly instructions; the clock shows HH.MM with the point flashing once a second; tune data is lost at power-off.
- ↑ 4.0 4.1 MZ-40K, Wikipedia (Japanese)—link(accessed 2026-10-21) The AC adaptor gives 11 V AC on a mini plug; it is rectified inside the unit and the mains frequency is the clock source; when setting the clock the user enters the time and the mains frequency; the volume control has a switch and is the main power switch.