Sharp MZ-1500 Troubleshooting Guide
Fault-finding on the Sharp MZ-1500 usually comes down to the internal 5 V power supply, the built-in Quick Disk drive or the keyboard. No Sharp service manual or fault-finding chart for the MZ-1500 has been found online. Its complete circuit diagram is printed in Radio Gijutsu-sha's Sharp MZ-1500 Technical Note (1984), and the circuit references below come from it.[1] Kogakusha's MZ-1500 Technical Manual also carries the circuit diagram.[2] The drive sections below draw on Sharp's documents for the MZ-1F11, which uses the same drive, and the rest on the owner Ohishi's repair notes.[3]
Warning: the power supply is inside the case and runs from the mains. Unplug the mains cable before opening the machine.
Quick reference
[edit | edit source]| Symptom | Probable cause | Action |
|---|---|---|
| Boot menu instead of a program | No bootable Quick Disk in the drive | Start-up |
| Kanji or kana drawn with dots out of place | Weak 5 V supply | Corrupted characters |
| Drive motor runs but the disk does not turn | Belt slack or broken | Disk does not turn |
| Disk turns slowly, some disks will not load | Friction at the head cam, older disks, weak supply | Disk turns stiffly |
| Frequent read errors | Dirty head, worn head pad | Read errors |
| Cannot save to a disk | Write-protect tab removed | Cannot save |
| Ordinary cassette recorder will not load | Signal polarity | Cassette |
| Text but no graphics | System switch 3 on | No graphics |
| A whole group of keys dead | Keyboard film cable | Keyboard |
| Board not found in the MZ-1U08 box | I/O address outside 00h to C7h | Expansion boards |
Start-up
[edit | edit source]The MZ-1500 holds no BASIC in ROM. At power-on it tries to boot from the Quick Disk; if there is no bootable disk, it shows a menu offering Quick Disk, floppy disk, cassette and the ROM monitor.[6] The menu on its own is not a fault.
If the screen stays blank and the drive's BUSY lamp never lights, check that the machine is on a 100 V supply, then open it and measure the 5 V output of the power supply.[6][4] The supply has that single output, so a supply with no 5 V output leaves the whole machine dead.[4] The 5 V reaches the main board on connector T-1, where C50 (100 µF) sits across it; measure there with the machine on.[1] See the Sharp MZ-1500 Capacitor Replacement Guide for the supply's capacitors.
If 5 V is present but nothing happens, check the reset circuit. The power-on reset comes from Q2, a PST518B-2, through R23 and C14 (3.3 µF); the reset switch feeds the same line through R31, with a 1 µF 50 V capacitor.[1] A reset line held active stops the CPU.
Corrupted characters
[edit | edit source]Ohishi's MZ-1500 drew kanji and kana with dots out of place once the kanji ROM and dictionary ROM boards were fitted in the main expansion slot. With the boards in the MZ-1U08 expansion box the characters were clean, which pointed at the machine's own power supply. After the supply was recapped, and in a second test after it was replaced with a modern 5 V switching supply, the boards worked in the main slot.[4]
- Remove option boards from the main slot and see whether the fault goes.
- Measure the 5 V output with the boards fitted.
- Recap the supply, or replace it; both are described in General Maintenance.
Quick Disk drive
[edit | edit source]The drive is the same Mitsumi drive that Sharp sold as the MZ-1F11.[3] One motor turns the disk and moves the head through a cam.[4] At rest the head sits at the inner edge of the disk, outside the recorded area. When the drive starts, the cam moves the head quickly to the outer edge, and it then follows the spiral track inwards, one pass taking 8 seconds; a save takes two passes, the second to verify. Four switches tell the circuit what the mechanism is doing: a media switch, a write-protect switch, a head position switch that marks the outer edge and starts the read or write, and a motor stop switch. A protection circuit keeps current out of the head while the power is switched on or off.[7]
Disk does not turn
[edit | edit source]If the motor can be heard but the disk does not seem to turn, or the head can never be heard moving, the drive belt is slack or broken. Ohishi uses a 40 mm diameter, 1.2 mm section belt.[4] The procedure is in General Maintenance.
Disk turns stiffly
[edit | edit source]Some disks turn freely while others make the drive labour and fail to load.[4]
- Disk version: disks marked A or B in a circle are the earlier type, which is said to stiffen with age; the later type, with an arrow and a square on the label, was improved.[3][4]
- Drive friction: the head is moved by a follower on the edge of a cam, and friction there slows the disk. Lubricating the cam edge and the head guide brought unreadable disks back on Ohishi's machine.[4]
- Power: a supply that can no longer deliver its full current also leaves the motor with less torque, though Ohishi found the drive itself the larger factor.[4]
Turning the trimmer beside the motor is often suggested. Ohishi found that it did little for torque and thinks it sets the motor speed.[4]
Read errors
[edit | edit source]- Clean the head. Sharp's MZ-1F11 manual makes this the first step whenever errors become frequent.[5]
- Try a disk known to be good, written on another machine if possible.
- Check the head pad. Sharp's service manual supplement for the MZ-1F11 gives the pad unit a life of 18,000 passes and, in its read-failure chart, calls for an off-track adjustment and a new pad when the read waveform at the test point is wrong.[8] The off-track adjustment itself is in the original MZ-1F11 service manual, which has not been found online; the supplement only refers to it.[8]
Sharp's manual also warns against running the drive continuously more than fifty times, and against opening the disk holder while the BUSY lamp is lit.[5]
Cannot save
[edit | edit source]Each side of a Quick Disk has its own write-protect tab. With the tab removed the side can be read but not written; cover the hole with tape to write to it again.[5] Sharp's write-failure chart for the MZ-1F11 goes on to the write-protect switch inside the drive if the tab is intact.[8] Quick Disks are written sequentially, so a single file cannot be deleted or enlarged in place; that is how the medium works, not a fault.[6]
Cassette
[edit | edit source]The MZ-1500 takes the MZ-1T03 data recorder on connector T-9 and an ordinary cassette recorder on the READ and WRITE sockets at the back.[6][1]
- An ordinary recorder that will not load or save: change system switch 1 on the back, which inverts the signal polarity for that recorder.[9][9]
- No signal on load: the READ socket (T-5) feeds the read circuit through C3 (1 µF) and C4 (10 µF). The WRITE socket (T-4) is fed through C10 (1 µF).[1]
- Data recorder motor not running: the motor line on T-9 is switched by Q1, a 2SA673.[1]
Keyboard
[edit | edit source]If individual keys are sluggish or unreliable, clean the contacts as described in General Maintenance.[4]
If a whole group of keys has stopped working, suspect the keyboard's connection to the main board. The keyboard is a matrix: the computer drives one of ten lines low at a time and reads eight return lines, so a bad contact on one line kills every key on it. Ohishi gives two examples: a bad contact on line 5 stops the letters A to H, and one on line 13 stops =, @, S, K, C, 3, - and the rest of that column.[4] Unplug the keyboard's film cable from the main board, clean the contacts and plug it back in carefully.[4]
Expansion boards
[edit | edit source]- A board that works in the machine's own slot but not in the MZ-1U08 expansion box is probably outside the box's I/O range, 00h to C7h. The MZ-1E05 floppy disk interface has to go in the machine's slot.[6][4]
- The MZ-1R12 SRAM board's standard addresses, $F8 to $FA, are also outside that range. Fit it in the main slot, or set it to $A8 to $AA to use it in the box.[4]
- The inner of the two connectors in the slot is for the MZ-1R18 RAM file board.[4]
Printer
[edit | edit source]The printer port can follow either the Sharp MZ standard or the Centronics standard, chosen with system switch 2 on the back: on for the MZ standard, which the MZ-1P08 and MZ-1P09 need, off for Centronics.[9][2]
No graphics
[edit | edit source]If text appears but graphics never do, check system switch 3 on the back. With it on, the graphics display is turned off; it is normally off.[9]
Sound
[edit | edit source]These are not faults:
- The two SN76489 chips each have their own output on the back, labelled 1 and 2, with no left or right; the internal speaker plays both mixed.[6]
- Most software treats the two chips as one six-voice mono source, and each rear output carries only one chip's voices, so take care when connecting external speakers.[6]
- A note played on both chips at once can cancel out, because the two square waves can be in opposite phase.[6]
If the rear outputs work but the speaker is silent, follow the path on the circuit diagram: the mixed sound passes through C18 and the volume control VR1 to the LM386 amplifier at 1I, and its output reaches the speaker connector T-3 through C62 (220 µF). The 8253's MZ-700 sound enters the SN76489 at 4F through C99, and the voice board's output enters the SN76489 at 3F through C29.[1]
MZ-700 software
[edit | edit source]Most MZ-700 software runs, but some programs fail under the MZ-1500's own BASIC, 5Z-001. Loading the MZ-700 system software itself solves this.[6]
Related pages
[edit | edit source]- Sharp MZ-1500
- Sharp MZ-1500 General Maintenance
- Sharp MZ-1500 Capacitor Replacement Guide
- Capacitor Failure Symptoms
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Nihon Maikon Kurabu (ed.), Sharp MZ-1500 Technical Note (シャープ MZ-1500 テクニカルノート), Radio Gijutsu-sha, Radio Gijutsu Sensho 151, first edition 15 December 1984; scan on the Internet Archive. Appendix 2, complete circuit diagram, pages 216 to 223: +5 V enters the main board on connector T-1 with C50 (100 µF) and C100 (0.1 µF) across it (page 219); power-on reset from Q2 (PST518B-2) through R23 and C14 (3.3 µF), and the reset switch through R31 with a 1 µF 50 V capacitor (page 219); data recorder connector T-9: 1 EX WRITE, 2 EX READ, 3 GND, 4 MOTOR, 5 SENCE, 6 +5 V, 7 WRITE, 8 READ, 9 GND, with the motor switched by Q1 (2SA673) (pages 216 and 222); cassette READ socket T-5 through C3 and C4, WRITE socket T-4 through C10 (pages 216 and 217); sound: SN76489s at 4F and 3F, the 8253 sound into 4F through C99 and the voice board into 3F through C29 (page 222); left and right outputs to T-13 through C16 and C17, mixed sound through C18 and the volume control VR1 to the LM386 at 1I, its output through C62 (220 µF) to the speaker connector T-3 (page 223); DIP switch table: 1 tape (normal or inverted), 2 printer (MZ or Centronics), 3 graphics display (page 223).
- ↑ 2.0 2.1 MZ (コンピュータ), Wikipedia (Japanese)—link(accessed 2026-10-21) From the MZ-1500 onwards the circuit diagram was not printed in the owner's manual; the MZ-1500 circuit diagram and monitor source were published in Kogakusha's MZ-1500 Technical Manual. The MZ-1500 has a DIP switch on the back to choose between the MZ printer standard and the Centronics standard.
- ↑ 3.0 3.1 3.2 MZ-1F11– Ohishi—link(accessed 2026-10-21) The external MZ-1F11 has the same drive inside as the MZ-1500's built-in drive (Mitsumi D280, top loading); two versions of disk, the earlier marked A or B in a circle, the later with an arrow and square and improved so that the inner disk turns less stiffly.
- ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 4.13 4.14 4.15 4.16 MZ-1500– Ohishi—link(accessed 2026-10-21) Owner's page, section "MZ-1500のメンテナンス". Power supply: with kanji and dictionary ROM boards in the main slot, characters were corrupted dot by dot; moving the boards to the expansion box cured it, and so did recapping or replacing the supply; single 5 V supply. Quick Disk drive: disks that turn stiffly and make a laboured noise, some giving errors; older disks marked A or B in a circle are said to stiffen; a weaker supply gives the motor less torque, but drive maintenance helps more; motor running but disk not turning, or the head never moving, means a slack or broken belt (40 mm by 1.2 mm); lubricate the head cam and head guide; the trimmer beside the motor seems to set speed rather than torque. Keyboard: individual sluggish keys from dirty contacts; key matrix of drive lines 1 to 10 and return lines 11 to 18; a bad contact on line 5 stops A to H, on line 13 stops =, @, S, K, C, 3, - and others; reseat or clean the film cable at the main board connector. Expansion: MZ-1U08 passes only $00 to $C7; MZ-1E05 and MZ-1R12 (at $F8 to $FA) belong in the main slot; MZ-1R12 can be set to $A8 to $AA.
- ↑ 5.0 5.1 5.2 5.3 Sharp, MZ-1F11 MZ Disk Drive instruction manual (File:Sharp MZ-1F11 Instruction Manual.pdf): cautions, page 1 (do not open or push the disk holder while the BUSY lamp is lit; do not operate the unit continuously more than fifty times or a malfunction may occur; if errors occur frequently, clean the head); write-protect tab, pages 4 and 5 (with the tab removed nothing can be saved, though the disk can be read; each side has its own tab; cover the hole with tape to write again); head cleaning, page 6.
- ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 MZ-1500, Wikipedia (Japanese)—link(accessed 2026-10-21) Boot order: Quick Disk first, then a boot menu (QD, floppy disk, cassette, ROM monitor); supplied BASIC 5Z-001 on Quick Disk; 100 V AC ±10%, 28 W; two SN76489, each with its own rear output labelled 1 and 2 with no left or right, mixed to mono for the speaker; both chips have a 50:50 duty cycle, so the same note sent to both chips can come out in opposite phase and cancel; an I/O port writes both chips at once; some MZ-700 software does not run under 5Z-001, but loading the MZ-700 system itself solves this; MZ-1U08 limited to 00h to C7h.
- ↑ Nihon Maikon Kurabu (ed.), Sharp MZ-1500 Technical Note, Radio Gijutsu-sha, 1984, pages 166 to 169: with a disk in the drive the head touches the medium; the head rests at the innermost edge, outside the read and write area; at the start of an operation the cam moves it quickly to the outer edge, and it then follows the spiral track inwards while reading or writing; one pass takes 8 seconds; a SAVE makes two passes, the second a verify; figure 3.17 shows the drive's write-protect switch, head position switch (which detects the outer edge and starts reading or writing), motor stop switch, media switch and a protection circuit that keeps current out of the head when the power is switched on or off, because a head stopped part-way could otherwise damage the recording.
- ↑ 8.0 8.1 8.2 Sharp, MZ-1F11 service manual supplement, code 00ZMZ1F11R//E (File:Sharp MZ-1F11 Service Manual Supplement.pdf): read-failure flow chart, page 3 (check the clock, the RDDT input and the waveform at the test point; if the waveform is wrong, adjust the off-track and replace the pad; otherwise check the read amplifier and digital conversion circuit); write-failure flow chart, page 2 (check the disk's write-protect tab and the write-protect switch of the drive unit); pad unit life 18,000 passes and replacement procedure, page 4. The supplement refers to an earlier MZ-1F11 service manual for anything not changed.
- ↑ 9.0 9.1 9.2 9.3 Nihon Maikon Kurabu (ed.), Sharp MZ-1500 Technical Note, Radio Gijutsu-sha, 1984, page 22, figure 1.7: four system switches on the back; switch 1 sets the polarity for an ordinary cassette recorder on the general cassette sockets (on: normal, off: inverted), to be changed if such a recorder will not read or write; switch 2 selects the printer interface (on: Sharp MZ standard, needed for the MZ-1P08 and MZ-1P09; off: Centronics); switch 3 turns the graphics display off when on (normally off); switch 4 is unused.