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Sharp MZ-80B General Maintenance

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Sharp MZ-80B
MZ-80B with its cassette deck above the keyboard (Darklanlan, CC BY 4.0)

Routine work on the Sharp MZ-80B covers the mains filter capacitors, the power supply's three regulated outputs, the software-controlled cassette deck and its belt, and the monitor. Component references and test values are from Sharp's MZ-80B service manual, which describes the 240 V, 50 Hz machine.[1]

Safety

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Warning: the MZ-80B has its mains switch, fuses, line filter and transformer inside the case, and a CRT at about 11 kV. Unplug the machine before opening it.

The power supply's primary board carries the fuses F101 and F102 (T630 mA), the line coil L101 and the two mains filter capacitors C101 and C102 (0.047 µF 250 V), which Sharp marks as safety parts.[2][3] Retro.Engineer described these as RIFA capacitors: on the MZ-80B they restored, one that had been missed during inspection exploded about ten seconds after the first power-on.[4] Check both before switching on a machine of unknown history, and replace them with capacitors rated for use across the mains. Before working near the tube or the flyback transformer, follow the CRT Discharge Procedure.[1]

Opening the case

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The service manual has no written disassembly procedure; its disassembled views show how the case, monitor, cassette deck and keyboard fit together.[5] Retro.Engineer describes the back of the case opening like a car bonnet to show the power supply, the logic board and the expansion cage, with the CRT driver board and a combined tape controller and audio amplifier board in the top housing. Removing the power supply meant taking most of the machine apart.[4]

Power supply checks

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The +12 V and +5 V outputs come from two SG3524N switching regulators (IC301 and IC401), and −5 V from an FS7905 regulator (IC201).[2] Sharp's fault charts give these intermediate voltages:[6]

MZ-80B power supply test points (Sharp fault charts)
Rail Check Expected
−5 V Across C201 (both ends) About 11 V
+12 V Pin 15 of IC301 (supply to the regulator) About 24 V
+5 V Pin 15 of IC401 (supply to the regulator) About 14 V

[6] Sharp took its waveforms with the supply loaded at 2.5 A on +5 V, 1.25 A on +12 V and 10 mA on −5 V.[6] Retro.Engineer checked the rails with the supply disconnected from the logic board before the first power-on.[4] The +12 V and +5 V outputs each have a 1 kΩ preset (VR301 and VR401), for which the manual gives no setting-up procedure.[2]

Cassette deck

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The MZ-80B's deck is driven by a reel motor and a capstan motor, with a brake solenoid and a panel solenoid, and the computer controls play, fast forward, rewind and eject.[7]

  1. Clean the heads, the capstan and the pinch roller with a soft cloth moistened with alcohol: open the cassette holder, take out the tape and press PLAY to bring the heads forward.
  2. Check the azimuth if tapes load with errors: put an oscilloscope on pin 8 of IC3102, play a TEAC test tape with a 3 kHz tone, and turn the azimuth screw for the largest waveform.
  3. Replace the drive belt if it has perished. Retro.Engineer replaced the belt on their machine, and Sharp's mechanism parts list includes a main belt and a motor pulley.[4][8]

The deck runs at 4.75 cm/s and Sharp lists C30 to C60 tapes.[1]

Loading software for testing

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Only the 2 KB IPL is in ROM, so a working machine needs the monitor and BASIC loaded from tape or disk.[9] Retro.Engineer made a boot tape by converting an MZF image of Sharp's SB-5510 tape BASIC to a WAV file with mzf2wave and recording it onto a blank cassette.[4]

Monitor

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The monitor's controls are volume, vertical hold, contrast, horizontal hold, brightness and focus; brightness and volume are also on the rear panel.[10] The manual has no adjustment procedure for the monitor; the fault chart is in the Sharp MZ-80B Troubleshooting Guide.

Capacitors

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The full list is in the Sharp MZ-80B Capacitor Replacement Guide. The power supply uses aluminium electrolytics only, while the CPU board has six 0.1 µF tantalums and the monitor board one 1 µF tantalum, C2010.[11]

Maintenance checklist

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  1. Unplug the machine and inspect C101 and C102 on the primary board.
  2. Check the outputs with the supply disconnected from the logic board, then under load.
  3. Clean the cassette heads, capstan and pinch roller and check the belt.
  4. Discharge the CRT before working near the tube or the flyback transformer.
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References

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  1. ↑ 1.0 1.1 1.2 Sharp Corporation, Service Manual, Personal Computer MZ-80B (File:Sharp MZ-80B Service Manual.pdf), specifications, printed pages 1 and 2 (PDF pages 3 and 4): AC 240 V 50 Hz; power supply outputs 5 V, −5 V, 12 V regulated and 12 V unregulated; 9-inch E2728B31 tube, 11.0 kV at zero beam; cassette 4.75 cm/s, C30 to C60 tapes. Hosted with a description at Sharp MZ-80B Service Manual.
  2. ↑ 2.0 2.1 2.2 Sharp, MZ-80B service manual (File:Sharp MZ-80B Service Manual.pdf), replacement parts list, power supply unit section (DBOXD0028PAZZ), PDF page 76: IC201 FS7905, IC301 and IC401 SG3524N; C101 and C102 RC-CZ0180PAZZ 0.047 µF 250 V, marked as safety parts; F101 and F102 T630 mA, F201 T1 A, F301 T1.6 A, F401 and F402 T3.15 A; VR301 and VR401 1 kΩ presets; L101 line coil.
  3. ↑ Sharp, MZ-80B service manual (File:Sharp MZ-80B Service Manual.pdf), power supply PWB section, printed page 40 (PDF page 41); also File:Sharp MZ-80B power supply board (service manual).png.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 Sharp MZ-80B, Retro.Engineer, 2024-11-22—link(accessed 2026-10-21) The back opens like a car bonnet, showing the power supply, logic board and expansion cage; CRT driver board and tape controller and audio amplifier board in the top housing; supply rails checked with the logic board disconnected; a RIFA capacitor exploded about ten seconds after first power-on and both were replaced with modern capacitors, which meant taking most of the computer apart to remove the power supply; belt replaced; C2010 found short-circuited after vertical collapse.
  5. ↑ Sharp, MZ-80B service manual (File:Sharp MZ-80B Service Manual.pdf), disassembled views, printed pages 45 to 50 (PDF pages 46 to 51).
  6. ↑ 6.0 6.1 6.2 Sharp, MZ-80B service manual (File:Sharp MZ-80B Service Manual.pdf), power supply trouble shooting chart, printed pages 17 and 18 (PDF pages 19 and 20), and waveforms, printed page 19 (PDF page 21): about 11 V across C201; about 24 V at pin 15 of IC301; about 14 V at pin 15 of IC401; with R309 or R405 open, a 0.2 V peak-to-peak signal at pin 12 of IC301 or IC401; waveforms taken with loads of 2.5 A on +5 V, 1.25 A on +12 V and 10 mA on −5 V.
  7. ↑ Sharp, MZ-80B service manual (File:Sharp MZ-80B Service Manual.pdf), cassette tape recorder section, printed pages 24 to 26 (PDF pages 26 to 28): block diagram with reel motor, capstan motor, brake solenoid, panel solenoid and relays RY1 to RY3; azimuth adjustment (oscilloscope on pin 8 of IC3102, TEAC test tape with a 3 kHz signal, turn the azimuth screw for maximum); head cleaning (open the holder, remove the tape, press play, clean the heads, capstan and pinch roller with a soft cloth moistened with alcohol); erase protection tabs.
  8. ↑ Sharp, MZ-80B service manual (File:Sharp MZ-80B Service Manual.pdf), "Cassette tape recorder mechanical parts", printed page 48 (PDF page 49): main motor assembly, motor pulley, main belt, flywheel capstan, record/playback and erase heads.
  9. ↑ MZ-80, Wikipedia (Japanese)—link(accessed 2026-10-21) MZ-80B: only an IPL in ROM, which loads the system from a floppy disk or the built-in data recorder into RAM.
  10. ↑ Sharp, MZ-80B service manual (File:Sharp MZ-80B Service Manual.pdf), display section specifications, printed page 2 (PDF page 4), and rear view, printed page 4 (PDF page 6).
  11. ↑ Sharp, MZ-80B service manual (File:Sharp MZ-80B Service Manual.pdf), replacement parts list: CPU board capacitors (PDF page 72); monitor TV board capacitors (PDF page 73); power supply capacitors (PDF page 76).


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