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Sharp MZ-80C General Maintenance

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Sharp MZ-80K
The MZ-80K, which shares the MZ-80C's basic design (Wolfgang Stief, CC0). The MZ-80C has a typewriter-layout keyboard and a green screen; no freely licensed photograph of one has been found.

The Sharp MZ-80C is a Japanese 100 V machine from 1979 with the same basic design as the Sharp MZ-80K, but with 48 KB of RAM, a typewriter-layout keyboard and a green monitor.[1] SharpMZ.net, which hosts Sharp's MZ-80K service manual, lists only a Japanese owner's manual for the MZ-80C.[2] The Sharp MZ-80K Service Manual covers the European MZ-80K, whose keyboard, display and power supply all differ from the C's, so check the C against it before following an MZ-80K procedure.

Mains supply

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Warning: the power switch, fuse and transformer are inside the case at mains voltage. Unplug the machine before opening it.

The MZ-80C runs from 100 V AC at 50 or 60 Hz, like the other Japanese MZ-80K series machines.[1] In a 230 V country it needs a step-down transformer. Japanese Wikipedia gives 20 W for the series, and Sharp gives about 45 W for the European MZ-80K.[1][3] Read the MZ-80C's rating plate and size the transformer to suit.

Opening the case

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SharpMZ.net's procedure for the MZ-80K is to remove the four screws in the base plate, lift the top half and lock the support hinge.[4] It is written for the MZ-80K; check the C's base for the same fixings before lifting it. Before working near the tube, follow the CRT Discharge Procedure. The MZ-80K's tube runs at about 11 kV, and the C's green tube has no published figure.[3]

Power supply

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The MZ-80K service manual covers only the European 220 V and 240 V supplies, so the C's 100 V supply has no published schematic.[3] If the C's CPU board matches the MZ-80K's, it needs +12 V, +5 V and −5 V at its power connector, where the MZ-80K has the 100 µF capacitors C36, C37 and C38.[5] Measure those rails. The European MZ-80K supply's four 10 µF tantalum capacitors are a reported failure, so look for tantalums on the C's supply and test them before running a machine of unknown history.[6]

Memory

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The MZ-80C came with 48 KB, the most the MZ-80K board takes.[1][3] On the MZ-80K, 48 KB means 4116 dynamic RAMs in all three banks, set by links on the headers CS1 and CS2; SharpMZ.net gives the link pattern for that setting.[4] Check the C's links against it before replacing any chips. On the MZ-80K the 4116s are socketed and fail: Adam Wilson found nine faulty in one 48 KB machine.[7]

Cassette recorder

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The C has a built-in cassette recorder.[1] Sharp's head cleaning and azimuth procedure for the MZ-80K deck is in Sharp MZ-80K General Maintenance#Cassette recorder: clean the heads, capstan and pinch roller with alcohol, and set the azimuth with a 3 kHz test tape.[8] Whether the C uses the same deck is not documented.

Keyboard and display

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The C's typewriter-layout keyboard and green monitor are not the MZ-80K's 78-key grid keyboard and black and white display, and Sharp's MZ-80K drawings and parts list for those units do not apply to them.[1][3]

Maintenance checklist

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  1. Confirm the mains supply is 100 V before switching on.
  2. Inspect the power supply for burnt or shorted tantalum capacitors.
  3. Measure +12 V, +5 V and −5 V at the CPU board.
  4. Check the RAM links and test the RAM if the machine shows memory faults.
  5. Clean the cassette heads, capstan and pinch roller.
  6. Discharge the CRT before working near the tube.
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 MZ-80, Wikipedia (Japanese)—link(accessed 2026-10-21) MZ-80C (1979): same basic design as the MZ-80K; built-in data recorder; 48 KB RAM as standard; full typewriter-layout keyboard; green monitor; more expensive parts than the MZ-80K; sold assembled. MZ-80K series in Japan: AC 100 V ±10 % 50/60 Hz, 20 W.
  2. ↑ MZ-80K Manuals, SharpMZ.net—link(accessed 2026-10-21) Lists the "Japanese MZ-80C Manual" and the MZ-80K Service Manual.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Sharp Corporation, Service Manual, Personal Computer MZ-80K (File:Sharp MZ-80K Service Manual.pdf), specifications, printed pages 1 and 2 (PDF pages 3 and 4): AC 220 V or 240 V 50 Hz, about 45 W; RAM 20 KB, extension to 48 KB; 10-inch black and white CRT with 11 kV anode voltage; 78 keys; power supply outputs 12 V 1.6 A, 5 V 1.6 A, −5 V 0.2 A. Hosted with a description at Sharp MZ-80K Service Manual.
  4. ↑ 4.0 4.1 MZ-80K Hints and Tips, SharpMZ.net—link(accessed 2026-10-21) MZ-80K: remove the four screws that secure the bottom plate, lift the top (keyboard, picture tube and cassette) and lock the support hinge; RAM banks RAM1 to RAM3 and link headers CS1 and CS2, with the 48 KB setting (CS1 all links straight across; CS2 1 to 16, 2 to 15, 3 to 13, 5 to 11).
  5. ↑ Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), circuit diagram (10) of the CPU board section, printed page 35 (PDF page 37): +12 V, +5 V, GND and −5 V at the power connector, with C36, C37 and C38 (100 µF 25 V).
  6. ↑ Sharp MZ-80K Power Supply repair– xAD / nIGHTFALL, nIGHTFALL Blog, 2013-01-13—link(accessed 2026-10-21) Four short-circuited tantalum capacitors in an MZ-80K power supply; owners report smoke and the F101 fuse blowing.
  7. ↑ 1980 Sharp MZ-80K Repair & Restoration– Adam Wilson, Adam's Vintage Computer Restorations, 2026-01-31—link(accessed 2026-10-21) MZ-80K upgraded to 48 KB; all 4116 DRAMs socketed; nine failed on a DRAM tester.
  8. ↑ Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), azimuth adjustment and head cleaning, printed page 23 (PDF page 25).


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