Sharp MZ-3500 General Maintenance
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Routine work on the Sharp MZ-3500 covers the mains supply, opening the main unit, checking the power supply's outputs, the fan, the battery for the clock, the floppy drives and the switch settings. Component references and item numbers are from Sharp's service manual, code 00ZMZ3500SM/E.[1] The manual has no disassembly or adjustment procedure, so the steps below follow its exploded views, circuit descriptions and connector tables.
Safety
[edit | edit source]Warning: the power supply unit inside the MZ-3500 is connected to the mains. Unplug the mains cable before removing the top cabinet.
Sharp's block diagram of the supply shows the mains input passing through a fuse and a noise filter to the power transformer. The switching regulators for +5 V and +12 V, the −12 V dropper and the alarm circuit all work from the transformer's secondary windings, after their own rectifier and smoothing circuits.[2] The mains wiring is therefore in the supply's input section and at the transformer primary.
Sharp listed separate power supply units for the 100 V series (DUNT-1035ACZZ) and the 200 V series (DUNT-1018ACZZ).[3] The export specification gives 220 V at 50 or 60 Hz and 100 W at most.[4] Find out which supply a machine has before connecting it to a different mains voltage.
Opening the main unit
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The exploded view in the parts guide shows how the main unit comes apart:[3]
- Unplug the mains cable, the keyboard and the displays, and take off any expansion unit fitted to the back.
- Remove the screws marked 31 in the exploded view and lift off the top cabinet (18).
- The power supply unit (17) sits in its cage on the left, held by screws (28). The MFD unit (25), with the drives, sits on its fixing angle (20) above the chassis (22).
- The main (CPU) board lies under the drives. SharpMZ.net's photograph of the board was taken with the floppy drives and the MFD interface board removed.[5]
- The MZ-1R03 graphic board goes in through a slot behind a lid on the front panel (2), and the bottom cabinet has a separate lid over the ROM LSI (10).[3][6]
Note where every connector goes before unplugging it.
Power supply checks
[edit | edit source]The supply feeds the CPU board through the PS connector, whose pins are listed in the CPU board connector table:[7]
| Pin | Signal | Pin | Signal |
|---|---|---|---|
| 1 | VGG | 2 | VDD |
| 3 | VCC | 4 | VCC |
| 5 | ALARM | 6 | GND |
| 7 | GND | 8 | GND |
[7] The supply's outputs are +5 V, +12 V and −12 V, with the alarm signal.[2] On the main CPU circuit diagram the CPU board has test pins for GND, VCC, VDD and VGG, and the rail capacitors are drawn with the positive end of the 220 µF capacitor on VDD and the negative end of the 100 µF capacitor on VGG, so VDD is the +12 V rail and VGG the −12 V rail.[8]
- Measure between the test pins on the CPU board, or at the PS connector, with the machine switched on: VCC should be +5 V, VDD +12 V and VGG −12 V.
- Check that ALARM is high once the machine is running. Sharp's timing chart shows it rising just after +5 V at switch-on and falling just before +5 V at switch-off.[2]
The parts list gives the supply two 2 kΩ trimmers, RV001 and RV002, and the circuit description gives each switching supply an adjusting control, but the manual does not say which trimmer sets which rail, and it gives no target voltage or tolerance.[9][2] Measure before touching either trimmer, mark its position first, and turn it only if a rail is clearly out.
Fan
[edit | edit source]The main unit has a fan motor (24) on its own fixing angle (21) at the rear of the bottom cabinet. The exploded view shows a 3 W, 33 Ω resistor (39) mounted beside it on a lug terminal.[3] With the case open, clean the dust from the fan, the power supply cage and the vents, and check that the fan turns freely and runs when the machine is switched on.
Clock battery
[edit | edit source]The calendar clock is a µPD1990AC on the CPU board, read by the sub-CPU through an 8255. Its supply pin is fed from VCC through a diode while the machine is on, and from a battery through a 1.5 kΩ resistor when it is off, with a 33 µF 16 V capacitor and a 0.01 µF capacitor on the same pin.[10] The parts list names the battery only by its Sharp code, UBATN1001ACZZ, and does not give its type or voltage.[11] Find it on the board, check it and the board around it for leakage and corrosion, and read its markings before ordering a replacement. See Battery Explosion, Capacitor or Corrosion Damage for cleaning leakage.
Floppy drives
[edit | edit source]The built-in drives are double-sided, double-density 5.25-inch units with 256 bytes per sector, 16 sectors per track and 80 tracks per disk.[12] Two service switch blocks on the CPU board, (A) and (B), tell the machine whether it has single-sided or double-sided drives and what is connected as an expansion drive. Sharp's factory settings are:[13]
| (A) 1 | (A) 2 | (A) 3 | (A) 4 | (B) 1 | (B) 2 | Use |
|---|---|---|---|---|---|---|
| OFF | OFF | OFF | ON | ON | ON | Factory setting for machines with single-sided drives |
| ON | OFF | OFF | ON | ON | ON | Factory setting for machines with double-sided drives |
| OFF | OFF | ON | ON | ON | ON | Single-sided optional MFD |
| ON | OFF | ON | ON | ON | ON | Double-sided optional MFD |
| OFF | ON | ON | ON | ON | ON | Test mode 1 |
| ON | ON | ON | ON | ON | ON | Test mode 2 |
| any | any | any | OFF | OFF | OFF | Individual CPU board test |
[13] Sharp says the user is not meant to change these switches. Note the settings before servicing and put them back afterwards. For cleaning and mechanical work on the drives, see Floppy Drive Repair.
User switches
[edit | edit source]A block of ten DIP switches, SW1, is reached through the bottom of the cabinet. Switches 1 and 2 select the printer type, 3 selects a high-resolution (400-line) or medium-resolution (200-line) display, 4 the decimal point character, 5 to 7 the RS-232C handshaking, 8 the shift-key mode and 9 the character set used on a 200-line display. Switch 10 is not connected.[13] A display that shows nothing useful is worth checking against switch 3 before suspecting the hardware.
Keyboard
[edit | edit source]The keyboards (MZ-1K02 US, MZ-1K03 UK, MZ-1K04 German and MZ-1K05 French) have 98 mechanical keys, an 80C49 or 8749 controller and a coiled cable with an 8-pin DIN plug that carries both the serial data and the keyboard's power.[14] The parts guide has an exploded view of the key unit. Clean the keys and the case with the cable unplugged.
Capacitors
[edit | edit source]The power supply's electrolytic capacitors are listed by reference number in the parts guide, and the CPU board's electrolytic types are listed without reference numbers. Both are covered in the Sharp MZ-3500 Capacitor Replacement Guide. General signs of failure are in Capacitor Failure Symptoms.
Maintenance checklist
[edit | edit source]- Find out whether the power supply is the 100 V or 200 V unit before plugging in.
- Unplug the mains cable before opening the case.
- Clean the fan, the supply cage and the vents.
- Check VCC (+5 V), VDD (+12 V) and VGG (−12 V) at the CPU board test pins, and that ALARM is high.
- Inspect the clock battery and the board around it for leakage.
- Note the SW1, (A) and (B) switch settings before any work, and check them afterwards.
- Run the self-check described in the Sharp MZ-3500 Troubleshooting Guide after any repair.
Related pages
[edit | edit source]- Sharp MZ-3500
- Sharp MZ-3500 Troubleshooting Guide
- Sharp MZ-3500 Capacitor Replacement Guide
- Sharp MZ-3500 Service Manual
- Recommended Tools
References
[edit | edit source]- ↑ Sharp, Service Manual, Personal Computer Model MZ-3500, code 00ZMZ3500SM/E (File:Sharp MZ-3500 Service Manual.pdf). Hosted with a description at Sharp MZ-3500 Service Manual.
- ↑ 2.0 2.1 2.2 2.3 Sharp, MZ-3500 service manual (File:Sharp MZ-3500 Service Manual.pdf), section 9, power circuit description, printed pages 87 to 89 (PDF pages 80 to 82): block diagram with mains input, fuse, noise filter, power line transformer, three rectifier and smoothing circuits, +12 V and +5 V power switching circuits with control and protection circuits, a shared oscillator, filter circuits, alarm circuit and −12 V dropper circuit; outputs +12 V, +5 V, −12 V and alarm; an overcurrent in the +5 V or +12 V circuit stops the oscillator and shuts off both supplies; each switching supply has an adjusting variable resistor; the alarm signal (PFD) rises after +5 V when the machine is switched on and falls before +5 V when it is switched off.
- ↑ 3.0 3.1 3.2 3.3 Sharp, MZ-3500 service manual (File:Sharp MZ-3500 Service Manual.pdf), parts guide, exteriors, page 2 (PDF page 110): 1 front cabinet assembly; 2 lid for graphic slot; 9 bottom cabinet; 10 lid for ROM LSI; 17 power supply unit, DUNT-1018ACZZ for the 200 V series and DUNT-1035ACZZ for the 100 V series; 18 top cabinet; 20 fixing angle for MFD; 21 fixing angle for fan; 22 chassis; 24 fan motor NFANP1001ACZZ; 25 MFD unit; 31 screw; 39 resistor, 3.0 W 33 Ω ±5 %. Exploded view, page 3 (PDF page 111).
- ↑ Technical data of the MZ-3500-series, SharpMZ.net—link(accessed 2026-10-21) Power: local area voltage, 220 V, 50/60 Hz, 100 W (max.); weight 15.3 kg with two drives.
- ↑ My MZ-3541, SharpMZ.net—link(accessed 2026-10-21) Photographs: "MZ-3541 opened. Power supply, MFD interface, floppies (covered)"; "MZ-3541 floppy drives, MFD interface, and power supply; floppy cover demounted"; "MZ-3541 Motherboard; floppies and MFD interface cards demounted".
- ↑ Sharp, MZ-3500 service manual (File:Sharp MZ-3500 Service Manual.pdf), section 1-4, MZ-1R03, printed page 3 (PDF page 4): graphic board inserted through the slot on the front panel; the MZ-1U02 expansion box is not required.
- ↑ 7.0 7.1 Sharp, MZ-3500 service manual (File:Sharp MZ-3500 Service Manual.pdf), 13-15, CPU P.W.B. connector terminal table (PDF page 104): PS connector pin 1 VGG, pin 2 VDD, pins 3 and 4 VCC, pin 5 ALARM, pins 6, 7 and 8 GND.
- ↑ Sharp, MZ-3500 service manual (File:Sharp MZ-3500 Service Manual.pdf), 13-1, main CPU and memory circuit diagram (PDF page 99): test pins (T) for GND, VCC, VDD and VGG; VDD to GND 220 µF 25 V (positive on VDD); VCC to GND 220 µF 16 V, four 100 µF 16 V and 0.1 µF (SC) 12 V capacitors for the 64K DRAMs; GND to VGG 100 µF 25 V (negative on VGG); reset gate fed by ALARM through 100 Ω with 1 µF 50 V to ground and a 10 kΩ pull-up, and by a power-on network of 33 kΩ, a diode and 1 µF 50 V; front-panel LED fed from VCC through 680 Ω on the LED board.
- ↑ Sharp, MZ-3500 service manual (File:Sharp MZ-3500 Service Manual.pdf), parts guide, power supply unit, pages 7 and 8 (PDF pages 115 and 116): RV001 and RV002 TM10K(PVB)B 2 kΩ trimmers.
- ↑ Sharp, MZ-3500 service manual (File:Sharp MZ-3500 Service Manual.pdf), section 8-1, clock circuit, printed page 81 (PDF page 74), and 13-2, sub-CPU circuit diagram (PDF page 100): µPD1990AC on port B of the µPD8255 with a 32 kHz crystal; VDD (pin 14) fed from VCC through a diode and from the battery through 1.5 kΩ, with 33 µF 16 V and 0.01 µF to ground.
- ↑ Sharp, MZ-3500 service manual (File:Sharp MZ-3500 Service Manual.pdf), parts guide, CPU PWB, pages 6 and 7 (PDF pages 114 and 115): battery UBATN1001ACZZ; 32 kHz crystal; µPD1990AC.
- ↑ Sharp, MZ-3500 service manual (File:Sharp MZ-3500 Service Manual.pdf), section 1-1, specification of the main unit, printed page 1 (PDF page 2).
- ↑ 13.0 13.1 13.2 Sharp, MZ-3500 service manual (File:Sharp MZ-3500 Service Manual.pdf), section 8-4, printed pages 85 and 86 (PDF pages 78 and 79): system SW1 (user operative through the cabinet bottom) and DIP switches (A) and (B) on the board, with the factory settings, test modes and individual CPU board test.
- ↑ Sharp, MZ-3500 service manual (File:Sharp MZ-3500 Service Manual.pdf), section 1-2, MZ-1K01 keyboard specification, printed page 2 (PDF page 3): 80C49 or 8749 controller, 4049 × 2 and 4514; 98 keys, mechanical contacts rated for 10,000,000 operations; serial data and power over a coiled cable with an 8-pin DIN plug; four LEDs; 467 × 35 × 190 mm, about 1.5 kg. Parts guide page 13 (PDF page 117): exploded view of the MZ-1K02 to MZ-1K05 key unit.