Sharp MZ-80K2 Troubleshooting Guide
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Fault-finding on the Sharp MZ-80K2 relies on Sharp's service manual for the MZ-80K, of which the K2 is the factory-assembled version. That manual covers the European 220 V and 240 V machines, so its power supply charts do not apply to the Japanese 100 V K2, while its checks for the CPU board, display, cassette recorder and keyboard can be used once the K2's board has been compared with the MZ-80K drawings.[1][2] The full set of Sharp's checks is in the Sharp MZ-80K Troubleshooting Guide.
Warning: mains voltage is present on the power switch, fuse and transformer, and the CRT anode runs at 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 |
| No picture | +12 V to the display, CRT heater, high voltage | MZ-80K display checks |
| Tape will not load | Heads, azimuth | MZ-80K cassette checks |
| Key does not register | Key switch, soldering, track | MZ-80K keyboard checks |
Power supply
[edit | edit source]- Check that the machine is on a 100 V supply. The K2 is a Japanese machine.[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 for shorts. On the European MZ-80K supply, four 10 µF tantalums are the reported failure: owners describe smoke from the supply and the mains fuse blowing.[3]
- Measure the outputs at the CPU board. On the MZ-80K they are +12 V, +5 V and −5 V, rated 1.6 A, 1.6 A and 0.2 A.[4]
Sharp's MZ-80K supply uses SG3524 switching regulators for +12 V and +5 V.[5] Whether the K2's 100 V supply uses the same circuit is not documented. Trace the K2's board before using the MZ-80K's test voltages.
CPU board and memory
[edit | edit source]Sharp's MZ-80K checks for a screen of garbage are the monitor ROM, the CPU, the character generator, the bus buffers and the RAM. A program that errors, a return to the monitor prompt, or errors after a long run point to the RAM.[6] The IC numbers are the MZ-80K's; match them to the K2's board first.
The K2 has 32 KB of RAM where the MZ-80K had 20 KB.[1] On the MZ-80K the 4116 dynamic RAMs are socketed and fail; Adam Wilson found nine faulty in one machine.[7] Test the K2's RAM out of circuit if it is socketed.
On an MZ-80K2E the CPU is soldered to the board.[1] It cannot be swapped to test it, so check the bus and the clock on the board before desoldering it.
Display, cassette and keyboard
[edit | edit source]The MZ-80K's checks for these units are in the Sharp MZ-80K Troubleshooting Guide. The K2 has the same 40-column display, a built-in cassette recorder and the grid keyboard, and its key caps have a matt finish.[1] A K2 fitted with the optional MZ-80TK typewriter keyboard will not match the MZ-80K keyboard drawings.[1] The MZ-80K2E has two single-colour LEDs where the K2 has one two-colour LED.[1]
Related pages
[edit | edit source]- Sharp MZ-80K2
- Sharp MZ-80K2 General Maintenance
- Sharp MZ-80K2 Capacitor Replacement Guide
- Sharp MZ-80K Troubleshooting Guide
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 MZ-80, Wikipedia (Japanese)—link(accessed 2026-10-21) MZ-80K2 (1980): assembled version, 32 KB RAM, nearly equivalent to the MZ-80K in software. MZ-80K2E (1981): CPU soldered without a socket, two single-colour LEDs in place of a two-colour LED. MZ-80K series in Japan: AC 100 V ±10 % 50/60 Hz.
- ↑ 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; power supply units DBOXD0004PAZZ and DBOXD0005PAZZ); trouble shooting guide, printed page 4 (check the 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 from the supply and the F101 500 mA fuse blowing.
- ↑ Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), specifications, printed page 1 (PDF page 3): power supply outputs 12 V 1.6 A, 5 V 1.6 A, −5 V 0.2 A.
- ↑ Sharp, MZ-80K service manual (File:Sharp MZ-80K Service Manual.pdf), wiring diagram of the power supply section, printed pages 37 and 38 (PDF pages 39 and 40).
- ↑ 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 (ROM, IC46, character generator, IC43, address bus IC44 and IC45, data bus IC36, IC37 and IC50, control IC35, RAM, IC52, IC53, IC56); RAM is the cause of errors in program execution, return to "MONITOR SP-1002" and errors after a long operation; RAM checker procedure.
- ↑ 1980 Sharp MZ-80K Repair & Restoration– Adam Wilson, Adam's Vintage Computer Restorations, 2026-01-31—link(accessed 2026-10-21) All the MZ-80K's 4116 DRAMs were socketed; nine failed on a DRAM tester.