Sharp MZ-6500 Troubleshooting Guide
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Fault-finding on the Sharp MZ-6500 starts with the built-in self check and Sharp's step-by-step procedure for the power supply. Both come from Sharp's service manual for the MZ-5600, the export version of the MZ-6500; component references are the MZ-5600's.[1][2] Safety notes and the supply adjustments are in the General Maintenance guide.
Self check
[edit | edit source]The IPL ROM holds a self check of the system RAM, the IPL ROM and the floppy drives.[3]
- With the machine off, set section 2 of the system DIP switch, on the bottom of the system unit, to ON.
- Switch on. The RAM size appears first, and each stage that passes gives a short beep.
- When asked, insert a formatted blank disk without a write-protect tab and press RESET on the front panel. Repeat for each drive.
- Switch off and set section 2 back to OFF.
| Message | Long beeps | Meaning |
|---|---|---|
| ERROR 00 | 10 | Stack area cannot be reserved; the check stops |
| ERROR 01 | 1 | Data bus error; the failing bit is shown |
| ERROR 02 | 1 | BHE or A0 error |
| ERROR 03 | 1 | Address line short circuit; the line is shown |
| ERROR 04 | 1 | Open address line, or a short to the supply or another signal |
| ERROR 05 | 1 | RAM read/write error; the bit and address are shown |
| ERROR 06 | 1 | DMA controller error |
| ERROR 07 | 1 | Written data lost |
| ERROR 08, 09 | 2 | High-order or low-order ROM error |
| ERROR 10 to 13 | 3 | Floppy drive errors (wrong data, protect, read/write, hardware) |
[3] If the RAM size shown does not match the RAM fitted, Sharp points to faulty RAM or a fault on address lines A18 or A19.[3]
Power supply
[edit | edit source]Supply shuts down
[edit | edit source]The +5 V and +12 V outputs have overcurrent protection. After an overload the supply may not restart at once: switch off, wait 30 to 40 seconds and switch on again. If it still does not start, a fuse may be open. The −12 V output is not protected, and a short on it can burn out the fuse resistor or the output transistor.[4]
Sharp's bench procedure
[edit | edit source]Sharp tests the supply board on the bench, fed from a variable transformer and loaded with a dummy load or the CPU unit, raising the input slowly while watching the controllers. Before removing the board, check it by eye for open wires, poor contacts, bad joints and burnt resistors, and unplug CN5 to check the transformer's primary side.[5]
| Step | Check | Parts if it fails |
|---|---|---|
| 1, 2 | +12 V loaded at 0.5 A; raise the input slowly with a scope on M2 pin 5. Input current must stay under 1 A at 10 V | RC1, RC2, Q3, Q4, Q6, Q7, D4, D7, D8, C3, C20 |
| 3 | Triangle waveform from the oscillator | M1, M2, C5, C25, F1 |
| 4 | Switching waveform at Q6, about 28 V pulses | Q5, Q6, Q7, M1, M2, D6 |
| 5 | +12 V present; set with VR2 (short-circuit current about 1 A) | M2, Q11, VR2, R36 |
| 6 | +5 V loaded at 0.2 A; switching waveform at Q3 with 22 V input | M1, Q4, Q5, D4, D5, C9, C10 |
| 7 | +5 V present; set with VR1 (short-circuit current 1 to 2 A) | M1, VR1, C9, C10 |
| 8 | −12 V within 15 % with 16 V AC input and a 0.05 A load | RC1, Q1, Q2, D1, R1 |
| 9 | ALARM rises from 0 V to +5 V at about 15 V AC input | Q8, Q9, Q10, D7, D8, D9, C20, C21, VR3 |
[5] The input voltages in the procedure, 10 to 22 V AC, are those at the board's input from the transformer secondary, which normally gives 22.5 V AC; they are not mains voltages. Sharp says not to adjust VR5.[5][6]
Disk-based diagnostics
[edit | edit source]Sharp also issued a service check program on disk for the MZ-5600A models, covering RAM and ROM, sound, video RAM and display functions, the floppy drives, the printer and RS-232C ports, the timer, the keyboard interface, expansion RAM, the 8087 and the clock's battery backup. The manual is hosted, but the test program disk is not.[7]
Related pages
[edit | edit source]- Sharp MZ-6500
- Sharp MZ-6500 General Maintenance
- Sharp MZ-6500 Capacitor Replacement Guide
- Sharp MZ-5600 Service Manual
- Sharp MZ-5600A Diagnostic Manual
References
[edit | edit source]- ↑ Sharp Corporation, Service Manual, Personal Computer Model MZ-5600 (code 00ZMZ5600SM/E). Hosted as File:Sharp MZ-5600 Service Manual.pdf; description at Sharp MZ-5600 Service Manual.
- ↑ MZ (コンピュータ), Wikipedia (Japanese)—link(accessed 2026-10-21) MZ-5600: the overseas model of the MZ-6500.
- ↑ 3.0 3.1 3.2 Sharp, MZ-5600 service manual, section 17, "Self check", printed pages 84 and 85 (PDF pages 85 and 86). Check items: RAM capacity, data bus, address bus, read/write of all locations, refresh signal, refresh, ROM, and floppy read/write. Procedure: set section 2 of the system DIP switch on the bottom of the System Unit to ON with the unit off; switch on; the total RAM capacity appears first; a short beep marks each stage passed; a long beep sounds once for a RAM error, twice for a ROM error and three times for a floppy error, with the error message shown for five seconds before the next step; after the RAM and ROM checks, insert a formatted blank diskette without a write-protect label and press RESET on the front of the System Unit to check each drive; when finished, switch off and set section 2 back to OFF. Messages: RAM-OK, ROM-OK, EXCHANGE DISK / PUSH RESET BUTTON, MFD-OK. Error messages (Table 47): ERROR 00 stack area cannot be reserved (10 beeps, check aborted); 01 data bus error, with the failing bit D15 to D0 shown; 02 BHE or A0 error; 03 hardware error such as an address line short circuit, with the address line A16 to A1 shown; 04 hardware error such as an open address line or a short to the supply or another signal; 05 RAM read/write error, with the error bit and the address 00000H to 70000H shown; 06 DMAC error; 07 written data was lost; 08 high-order ROM error; 09 low-order ROM error; 10 floppy reads or writes wrong data; 11 floppy protect error; 12 floppy read/write error; 13 hardware error. RAM capacity message 128 KB, 256 KB or 512 KB: if it does not match the fitted RAM, the RAM is defective or there is a fault on address lines A18 or A19.
- ↑ Sharp Corporation, MZ-5500/5600 Technical Reference Vol. 2 (Hardware) (File:Sharp MZ-5500 and MZ-5600 Technical Reference Vol. 2.pdf), section 16, "Power supply unit", PDF pages 109 and 110: overcurrent protection on +5 V and +12 V turns the output off on a short or abnormal load; the unit may not recover immediately after the cause is removed, in which case switch off, wait 30 to 40 seconds and switch on; if power still does not come on, a fuse may be open or there may be a fault; −12 V has no overcurrent protection, and a short may burn out the fuse resistor or damage the output stage transistor.
- ↑ 5.0 5.1 5.2 Sharp, MZ-5600 service manual, section 16-3, "Troubleshootings", printed pages 81 to 83 (PDF pages 82 to 84). (1) Hints and tips: do not remove the board at first; check visually for open wires, contact failures, improper soldering and burnt resistors; unplug the power input connector (V1, V2: CN5) and check for a failure on the primary side of the power transformer; tools: oscilloscope, 200 V AC regulator (Slidac), voltmeter, ammeter, dummy load or CPU unit, power transformer. (2) Checking the trouble cause: 1-1 +12 V output loaded at 0.5 A, +5 V and −12 V unloaded; 1-2 oscilloscope on M2 pin 5 at 1 V/div, 5 µs/div; 2-1 slowly raise the input; switch off if the input current exceeds 1 A by 10 V (RC1, RC2, Q3, Q4, Q6, Q7, D4, D7, D8, C3, C20); 3-1 check for a triangle waveform (if not: M1, M2, C5, C25, F1); 4-1 watch the waveform between Q6 and VCE while raising the input, about 28 V pulses (Q5, Q6, Q7, M1, M2, D6); 5-1 set +12 V with VR2, short-circuit current of +12 V about 1 A (M2, Q11, VR2, R36); 6-1 +5 V loaded at 0.2 A, +12 V and −12 V unloaded; 6-2 watch the waveform between Q3 and VCE, input at 22 V, and check it oscillates (M1, Q4, Q5, D4, D5, C9, C10); 7-1 set +5 V with VR1, short-circuit current of +5 V 1 to 2 A (M1, VR1, C9, C10); 8-1 −12 V loaded at 0.05 A, +5 V at 0.2 A; 8-2 raise the input slowly to 16 V AC and check −12 V ± 15 % (RC1, Q1, Q2, D1, R1); 9-1 connect +5 V to ALARM through 1 kΩ; 9-2 raise the input slowly to 18 V AC and check ALARM changes from 0 V to +5 V at about 15 V AC (Q8, Q9, Q10, D7, D8, D9, C20, C21, VR3); do not adjust VR5.
- ↑ Sharp, MZ-5600 service manual, section 16-2 (1), "Rectifier circuit", printed page 80 (PDF page 81): the power transformer converts the AC input to a secondary output of 22.5 V AC, rectified to 29 V DC, from which the +5 V and +12 V outputs are derived; the −12 V rectifier is a separate circuit.
- ↑ Sharp Corporation, Diagnostic Manual for Model MZ5600A (DKOG-1005ACZZ) (File:Sharp MZ-5600A Diagnostic Manual.pdf): applicable models MZ-5631A, MZ-5641A, MZ-5645A and MZ-5646A; tools required: RS-232C interface cable, test program media, two fresh media; the test program is loaded from the test program media; tests 1 to 12 (RAM and IPL ROM, sound, VRAM, display functions, MFD, printer interface, RS-232C interface, timer, key interface, expansion DRAM, expansion VRAM, 8087); III, RTC battery backup test (service check program 11); IV, RAM file (MZ-1R32) test. Described at Sharp MZ-5600A Diagnostic Manual.