Sharp MZ-80C Troubleshooting Guide
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The Sharp MZ-80C shares the MZ-80K's basic design but has a typewriter-layout keyboard, a green monitor, 48 KB of RAM and a 100 V Japanese power supply.[1] SharpMZ.net, which hosts the MZ-80K service manual, lists only a Japanese owner's manual for the C.[2] Sharp's checks for the European MZ-80K, in the Sharp MZ-80K Troubleshooting Guide, are the closest guide for the CPU board and the cassette recorder, once the C's boards have been compared with the MZ-80K drawings. They do not cover the C's keyboard, display or power supply.[3]
Warning: mains voltage is present on the power switch, fuse and transformer, and the CRT runs at a high voltage (about 11 kV on the MZ-80K). Unplug the machine before opening it and follow the CRT Discharge Procedure.
Quick reference
[edit | edit source]| Symptom | First check | Where to look |
|---|---|---|
| Dead | Mains voltage (100 V), fuse, power supply tantalum capacitors | Power supply |
| Garbage on screen or memory errors | RAM, ROM, CPU and bus buffers | CPU board and memory |
| Tape will not load | Heads, azimuth | MZ-80K cassette checks |
| No picture or key faults | Display or keyboard of the C's own design | Display and keyboard |
Power supply
[edit | edit source]- Check that the machine is on a 100 V supply.[1]
- If it is dead, unplug it, open it and check the mains fuse and the transformer.
- Look for tantalum capacitors on the supply board and test them. On the European MZ-80K supply, four 10 µF tantalums short and cause smoke or a blown mains fuse.[4]
- Measure the outputs at the CPU board. The MZ-80K's are +12 V, +5 V and −5 V.[3]
The C's 100 V supply has no published schematic, so trace it before relying on the MZ-80K's test voltages.
CPU board and memory
[edit | edit source]Sharp's MZ-80K checks for a screen of garbage cover the monitor ROM, the CPU, the character generator, the bus buffers and the RAM, and point to the RAM for program errors, a return to the monitor prompt and errors after a long run.[5] The IC numbers in those checks are the MZ-80K's. Match them to the C's board before using them.
The C has 48 KB of RAM.[1] On the MZ-80K that means three banks of 4116 dynamic RAMs, and the 4116s are a known failure: Adam Wilson found nine faulty in one 48 KB MZ-80K.[6][7] If the C's RAM is socketed, test it out of circuit.
Display and keyboard
[edit | edit source]The C's green monitor and typewriter keyboard are different units from the MZ-80K's black and white display and grid keyboard.[1][3] Sharp's MZ-80K display chart starts with the +12 V supply, the CRT heater and the high voltage, and its keyboard list with soldering, the key switch and the board track; those first checks apply to any such unit, but the MZ-80K's component numbers do not.[8]
Cassette recorder
[edit | edit source]Clean the heads, capstan and pinch roller first. Sharp's MZ-80K cassette checks and azimuth procedure are in the Sharp MZ-80K Troubleshooting Guide#Cassette recorder.[9]
Related pages
[edit | edit source]- Sharp MZ-80C
- Sharp MZ-80C General Maintenance
- Sharp MZ-80C Capacitor Replacement Guide
- Sharp MZ-80K Troubleshooting Guide
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 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; full typewriter-layout keyboard; green monitor; more expensive parts than the MZ-80K. MZ-80K series in Japan: AC 100 V ±10 % 50/60 Hz.
- ↑ MZ-80K Manuals, SharpMZ.net—link(accessed 2026-10-21) Lists the "Japanese MZ-80C Manual" and the MZ-80K Service Manual.
- ↑ 3.0 3.1 3.2 Sharp Corporation, Service Manual, Personal Computer MZ-80K (File:Sharp MZ-80K Service Manual.pdf): specifications, printed pages 1 and 2 (AC 220 V or 240 V; 10-inch black and white CRT; 78 keys; power supply outputs 12 V 1.6 A, 5 V 1.6 A, −5 V 0.2 A); trouble shooting guide, printed page 4 (power supply, display, cassette recorder, keyboard and CPU board in turn). Hosted with a description at Sharp MZ-80K Service Manual.
- ↑ 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 replaced with electrolytics; owners report smoke and the F101 500 mA fuse blowing.
- ↑ Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), CPU board section, printed pages 5 to 10 (PDF pages 7 to 12): memory block checks; RAM causes errors in execution, a return to "MONITOR SP-1002" and errors after a long operation; RAM checker procedure.
- ↑ MZ-80K Hints and Tips, SharpMZ.net—link(accessed 2026-10-21) MZ-80K 48 KB arrangement: RAM banks 1 to 3 all 16 KB (4116), with the CS1 and CS2 link settings.
- ↑ 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; socketed 4116 DRAMs; nine failed on a DRAM tester.
- ↑ Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), display section trouble shooting chart, printed page 18 (PDF page 20); keyboard section, printed page 24 (PDF page 26).
- ↑ 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).