Jump to content

Sharp MZ-80K General Maintenance

From RetroTechCollection
Sharp MZ-80K keyboard
MZ-80K graphics keys, each a printed key top under a clear key cover (Marcin Wichary, CC BY 2.0)

Routine work on the Sharp MZ-80K covers opening the hinged case, checking the three power supply outputs, cleaning and aligning the built-in cassette recorder, and looking after the socketed chips on the CPU board. Component references and test values are from Sharp's MZ-80K service manual, which covers the European 220 V and 240 V machines.[1]

Safety

[edit | edit source]

Warning: the MZ-80K has its mains switch, fuse and transformer inside the case, and a CRT that runs at about 11 kV. Unplug the mains lead before opening the machine.

The power supply schematic shows the mains input SO101 through the double-pole switch SW101 to the fuse F101 (T500 mA), the capacitor C101 (0.047 µF 250 V) across the supply, and the transformer T101, which has a thermal fuse in its primary.[2] The display's anode voltage is about 11 kV with no beam current.[3] Before working near the tube or the flyback transformer, follow the CRT Discharge Procedure.

Opening the case

[edit | edit source]

The top half of the MZ-80K, with the keyboard, the picture tube and the cassette recorder, is hinged at the back and opens upwards. SharpMZ.net gives the procedure:[4]

  1. Switch off and unplug the mains lead.
  2. Turn the computer upside down and remove the four screws that hold the bottom plate.
  3. Turn it the right way up and lift the top.
  4. Lock the support hinge before working underneath.

Sharp's exploded view shows the hinge and the support arm that holds the top open, and the holder for the CPU board in the base.[5] AKIBA PC Hotline! notes the display adjustment knobs at the upper left at the back, reached with the top open.[6] Adam Wilson removed the CPU board and the power supply from his machine to clean and service them before powering it up.[7]

Power supply checks

[edit | edit source]

The supply makes +12 V and +5 V with two SG3524 switching regulators fed from about 23 V DC, and −5 V with a µA78MGU regulator on its own transformer winding.[2] Sharp's fault charts give these voltages to measure. The 220 V unit (DBOXD0004PAZZ) and the UK unit (DBOXD0005PAZZ) differ only in the AC and DC figures for the −5 V section.[8]

MZ-80K power supply test points (Sharp fault charts)
Measure Where 220 V unit UK 240 V unit
Mains Across C101 220 V AC 240 V AC
−5 V winding Orange lead 9 V AC 10 V AC
−5 V reservoir Across C201 10 V DC 11 V DC
−5 V output Across C202 −5 V DC −5 V DC
Main winding Yellow lead 20 V AC 20 V AC
Main reservoir Across C301 23 V DC 23 V DC
+12 V output Across C404 12 V DC 12 V DC
+5 V output Across C507 5 V DC 5 V DC

[8] Sharp rates the outputs at 12 V 1.6 A, 5 V 1.6 A and −5 V 0.2 A.[3] Each output has a 1 kΩ preset (VR201 for −5 V, VR401 for +12 V and VR501 for +5 V), but the service manual gives no procedure for setting them.[2] Leave them alone unless a rail is out and the rest of the supply has been checked.

C101, across the mains after the switch, is marked on the schematic and in the parts list as a safety part. In the machine Adam Wilson restored it was a polymer X/Y capacitor soldered to the power switch.[2][9][7] Use a replacement rated for connection across the mains if it is ever changed.

Cassette recorder

[edit | edit source]

Cleaning the heads

[edit | edit source]

Sharp's instructions: open the cassette holder, remove the tape, press PLAY, and clean the heads, the capstan and the pinch roller with a soft cloth moistened with alcohol. Sharp says to do this often, because dust and tape residue spoil both recording and playback.[10] To get better access to the heads, push in the two plastic lugs that stop the lid opening further; the lid then opens much wider.[4] Maurice Hawes of the Sharp Users Club found that the heads needed regular cleaning and that the PRESS PLAY contact needed an occasional rub with fine emery paper.[11]

Head azimuth

[edit | edit source]

If tapes load with errors after cleaning, check the azimuth. Sharp's procedure:[10]

  1. Connect an oscilloscope to the collector of Q3003.
  2. Play a TEAC test tape with a 3 kHz signal recorded on it.
  3. Turn the head azimuth adjusting screw for the largest waveform.

Belts, motor and protection

[edit | edit source]

The deck runs at 4.75 cm/s with a 12 V electronically governed motor.[3] Sharp's list of cassette mechanism parts gives part numbers for the main belt (94R06580KCTRM), the counter belt (94R05480KCTRM), the pinch roller assembly (94R01480KCTRM), the record/playback head (94R06080KCTRM), the erase head (94R06180KCTRM) and the motor (94R06480KCTRM), but no belt sizes.[12] The record button is blocked when the cassette's erase-protection tabs are removed or when no cassette is fitted. Sharp warns that forcing it can cause a fault.[10]

CPU board and chips

[edit | edit source]

Sharp's handling precautions for the board's MOS chips: ground yourself through a resistor of several megohms, lay chips on grounded foil, use a soldering iron with no leakage current (Sharp suggests a 6 V, 12 W iron), hold chips by the package, check the orientation before inserting them, switch off before removing them, and solder quickly.[13] All the major chips on the MZ-80K are in sockets.[11] Adam Wilson cleaned the sockets with contact cleaner and tested every 4116 dynamic RAM out of circuit; nine had failed.[7]

The memory size is set by links on the two 16-pin headers CS1 and CS2, and the RAM sits in three banks of sockets marked RAM1 to RAM3. SharpMZ.net lists the link settings for 20, 24, 36 and 48 KB.[4] Record the links before removing anything. The monitor ROM is a 2332, which can be replaced by a 2532 EPROM with no changes to the board.[4]

Keyboard

[edit | edit source]

The keyboard unit (DKEY-0005PAZZ) uses mechanical key switches, each with a separate key top and key cover.[9] Sharp's fault list for a key that does not register is poor soldering, a faulty key switch or a broken track on the keyboard board.[14]

Display

[edit | edit source]

The display controls are volume, vertical hold, contrast, horizontal hold, brightness and focus.[3] The service manual has no adjustment procedure for the display; its display section is a fault chart with waveforms.[15]

Capacitors

[edit | edit source]

The power supply's four 10 µF tantalum capacitors are the parts owners report failing. All the electrolytic and tantalum capacitors in the machine are listed in the Sharp MZ-80K Capacitor Replacement Guide. General signs of failure are in Capacitor Failure Symptoms.

Maintenance checklist

[edit | edit source]
  1. Unplug the machine, open the top and lock the support hinge.
  2. Inspect the power supply for burnt tantalum capacitors and check C101 on the mains switch.
  3. Measure +12 V across C404, +5 V across C507 and −5 V across C202.
  4. Clean the cassette heads, capstan and pinch roller, and check the azimuth if loading is unreliable.
  5. Reseat or test the socketed RAM if the machine shows memory faults.
  6. Discharge the CRT before working near the tube or the flyback transformer.
[edit | edit source]

References

[edit | edit source]
  1. ↑ Sharp Corporation, Service Manual, Personal Computer MZ-80K (File:Sharp MZ-80K Service Manual.pdf). Hosted with a description at Sharp MZ-80K Service Manual.
  2. ↑ 2.0 2.1 2.2 2.3 Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), wiring diagram of the power supply section, printed pages 37 (220 V unit DBOXD0004PAZZ) and 38 (UK unit DBOXD0005PAZZ), PDF pages 39 and 40; also File:Sharp MZ-80K power supply circuit (service manual).png: SO101, SW101, F101 T500 mA, C101 0.047 µF 250 V, T101 with thermal fuse TF; −5 V: F201 T500 mA, D201, C201 2200 µF 16 V, IC1 µA78MGU, R201, VR201 (1 kΩ), C202 470 µF 10 V, L201, F202 T315 mA; D301 and D302 into C301 to C304 2500 µF 35 V; +12 V: IC2 SG3524, Q401, Q402, L401, C404 2200 µF 16 V, L402, F401 T1.6 A, VR401 (1 kΩ); +5 V: IC3 SG3524, L501, Q501, Q502, L502, C507 3300 µF 10 V, L503, F501 T1.6 A, VR501 (1 kΩ); C401, C501, C502 and C509 10 µF 35 V.
  3. ↑ 3.0 3.1 3.2 3.3 Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), specifications, printed pages 1 and 2 (PDF pages 3 and 4): power supply outputs 12 V 1.6 A, 5 V 1.6 A, −5 V 0.2 A; display DUTT0004PAZZ, 240NB4 tube, 12 V 1.1 A, high voltage 11.0 kV at zero beam (10.0 kV minimum, 12.0 kV maximum), controls volume, V-hold, contrast, H-hold, brightness and focus; cassette recorder KTRC-0004PAZZ, 4.75 cm/s, electronic governor motor (12 V), tapes C30 to C120.
  4. ↑ 4.0 4.1 4.2 4.3 MZ-80K Hints and Tips, SharpMZ.net—link(accessed 2026-10-21) Switch off and disconnect from the mains; turn the computer upside down and remove the four screws that secure the bottom plate; turn it the right way up and lift the top (keyboard, picture tube and cassette); lock the support hinge. Cassette lid: push in the two plastic lugs that stop the lid opening further. RAM sockets RAM1 to RAM3, link headers CS1 and CS2; monitor ROM 2332, replaceable by a 2532 EPROM without modification.
  5. ↑ Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), "Key Board Section and Others" exploded view, printed page 56 (PDF page 55), and parts list, printed page 48 (PDF page 50): CPU board holder, hinge, support arm and arm fixing angle.
  6. ↑ モニタ一体型のイカすヤツ「シャープ MZ-80K」、パソコンを身近にしてくれた人気機種, AKIBA PC Hotline! (Impress), 2020-08-25—link(accessed 2026-10-21) The case opens like a car bonnet; knobs for adjusting the display brightness and so on are at the upper left rear.
  7. ↑ 7.0 7.1 7.2 1980 Sharp MZ-80K Repair & Restoration– Adam Wilson, Adam's Vintage Computer Restorations, 2026-01-31—link(accessed 2026-10-21) Mainboard removed for servicing before power-on; mainboard cleaned, IC sockets cleaned with contact cleaner, solder joints inspected, tantalum and aluminium electrolytic capacitors replaced; 4116 DRAMs tested, nine failed; power supply removed, cleaned and tested unloaded, outputs (+5 V, −5 V, +12 V) in tolerance; a polymer X/Y capacitor soldered directly to the power switch; four 10 µF tantalum capacitors in the supply.
  8. ↑ 8.0 8.1 Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), trouble shooting charts for the power supply, printed pages 13 (DBOXD0004PAZZ) and 15 (DBOXD0005PAZZ for the UK), PDF pages 15 and 17; also File:Sharp MZ-80K power supply trouble shooting chart (service manual).png.
  9. ↑ 9.0 9.1 Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), replacement parts list, printed pages 43 to 48 (PDF pages 45 to 50): C101 RC-CZ0174PAZZ 0.047 µF 250 V Mylar, marked as a safety part; F101 and F201 T500 mA, F202 T315 mA, F401 and F501 T1.6 A; keyboard unit DKEY-0005PAZZ with mechanical key switches, key tops and key covers.
  10. ↑ 10.0 10.1 10.2 Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), cassette tape recorder section, printed pages 21 to 23 (PDF pages 23 to 25): trouble shooting chart; azimuth adjustment (synchroscope on the collector of Q3003, TEAC test tape with a 3 kHz signal, turn the head azimuth adjusting screw for maximum waveform); head cleaning (open the holder, remove the tape, push the play button, clean the heads, capstan and pinch roller with a soft cloth moistened with alcohol); erase protection (record button blocked when the cassette tabs are removed or no cassette is fitted; pushing it hard may cause a fault).
  11. ↑ 11.0 11.1 Maurice Hawes, "A Brief History of the MZ-80K", SUC Magazine, November 1999, vol. 19 no. 3, p. 7, reproduced at A Brief History of the MZ-80K, SharpMZ.net—link(accessed 2026-10-21) The tape heads require regular cleaning and the PRESS PLAY contact an occasional rub with fine emery paper; all the major chips are in sockets.
  12. ↑ Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), "Cassette tape recorder mechanical parts", exploded view and parts table on the unnumbered page between printed pages 48 and 53 (PDF page 51).
  13. ↑ Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), "Precautions on handling LSI's and IC's", printed page 3 (PDF page 5).
  14. ↑ Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), keyboard section, printed page 24 (PDF page 26).
  15. ↑ Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), display section, printed pages 17 to 20 (PDF pages 19 to 22).


Retrieved from "https://retrotechwiki.com/index.php?title=Sharp_MZ-80K_General_Maintenance&oldid=28535"