Sharp MZ-2500 Troubleshooting Guide

Front of an MZ-2500 with the pocket open: MODE, CRT, VOLUME, RESET and IPL (photo: Jun Sasaki, AKIBA PC Hotline!)

Fault-finding on the Sharp MZ-2500 starts with the settings that stop a working machine from appearing to work: the 100 V supply, the rear POWER SELECT switch, the mode and CRT switches in the front pocket and the monitor output switches on the back. After that the IPL's own start-up keys, including an undocumented RAM test, help to separate board faults from drive and media faults. The checks below use Sharp's dealer material, the owner's manual as summarised by Japanese Wikipedia, and owners' reports.

Warning: the MZ-2500 has its mains supply inside the case and a mains outlet on the back. Unplug the mains lead before removing the cover.

Quick reference

Symptoms, causes and actions

Symptom	Probable cause	Action
Dead, no lamps	Mains voltage, power switch, POWER SELECT setting, internal supply	No power
Lamps on, no picture	CRT line switch, DIGITAL/ANALOG switch, wrong output or monitor	No picture
"Insert System Disk"	No system disk in the boot drive	Start-up messages
Crashes or garbled screen	RAM, video RAM	Memory test
Keyboard dead	Wrong socket, cable, keyboard	Keyboard
Volume, RESET or IPL intermittent	Worn contacts in the front pocket	Front pocket controls
Disk errors	Drive numbering, heads, media	Floppy drives
Tape will not load	Heads, pinch roller, mode	Voice recorder
Clock loses the date	Clock backup battery	Clock

No power

1. Check the supply. Sharp rates the MZ-2500 for 100 V ±10% at 50 or 60 Hz; outside Japan it must run from a step-down transformer.
2. The power switch is on the left side of the case, not the front.
3. Set the rear POWER SELECT switch to NORMAL. The other position, REMOTE, belongs to the standby arrangement for answering telephone calls automatically.
4. If the machine is still dead, unplug it, remove the cover and inspect the internal supply for a blown fuse, burnt parts and leaking or swollen capacitors. Record what is fitted before replacing anything, as described in the Sharp MZ-2500 Capacitor Replacement Guide.

No picture

Most cases of no picture on a working MZ-2500 are settings.

• The CRT switch in the front pocket selects 200 or 400 lines. The MiSTer reimplementation describes these as a 15 kHz monitor (200 lines) and a 24 kHz monitor (400 lines), with software reading the switch. A 15 kHz monitor will show nothing usable with the switch at 400. Set the switch to suit the monitor and press IPL.
• The rear has separate monochrome (B/W CRT) and colour (COLOR CRT) outputs, each with its own DIGITAL/ANALOG switch. Sharp lists video (B/W), RGB, RGBI and linear (analogue) RGB among the CRT interfaces. Check that the monitor is on the output you are using and that the switch beside it matches the monitor's input.
• The Sharp Users Club got their first picture from an MZ-2500 on an MZ-5600 monochrome monitor, which showed the IPL message.
• In MZ-80B mode the picture is black and white, which is normal.

Start-up messages and boot keys

With no system disk, the IPL shows "Insert System Disk"; this message means the board is running. Keys held while the IPL starts change the boot device:

IPL start-up keys (owner's manual, as summarised by Japanese Wikipedia)

Key	Effect
C	Boot from the voice recorder whatever the mode
1, 2, 3, 4	Boot from drive FD1, FD2, FD3 or FD4
E	Swap the internal drives (as FD3 and FD4) with the external drives (as FD1 and FD2)
/	Load and run a program from a ROM in I/O space
R	Set the RS-232C speed for MZ-2000 and MZ-80B modes

Holding HELP at power-on gives a choice between BASIC-M25 and BASIC-S25.

Memory test

Japanese Wikipedia, citing Dempa Shinbunsha's Super MZ 活用研究 (page 260), lists an undocumented test: hold B while the IPL starts and the machine tests the main RAM and graphics RAM in 46 blocks, showing "No" or "Good" for each block. The same source says some of the undocumented functions were removed on later models, so the test may not be present on an MZ-2531 or MZ-2520. A "No" against a block points to the RAM chips for that block; if the optional MZ-1R26 RAM card or MZ-1R27 video RAM card is fitted, remove it and test again to see whether the fault moves with the card.

Wrong mode or odd behaviour

• The mode switch (MZ-2500, MZ-2000/2200 or MZ-80B) is read at reset, so press IPL after changing it.
• Holding X or Z while the IPL starts gives the MZ-80B or MZ-2000 mode at 6 MHz. In these modes the sound and the voice recorder timing are wrong, because software timing loops run faster; this is not a fault.

Keyboard

• There are keyboard sockets at the front right and on the right side; only one can be used at a time. Try the other socket.
• The plug is an 8-pin mini-DIN: pin 1 is +5 V, pin 2 is RSTN, pins 3 to 7 are KD0 to KD4 and pin 8 is MPX, with ground on the connector shell. With the keyboard unplugged and the machine on, measure +5 V between pin 1 and the socket shell. If it is present, the fault is likely in the cable or the keyboard.
• The keyboard has its own controller (LZ91A17), and the main unit has a matching key controller (LZ91A21).
• An MZ-2520 keyboard does not fit the other models, and the other way round.

Front pocket controls

The volume slider and the RESET and IPL buttons in the pocket tend to develop poor contacts with age on the MZ-2511, MZ-2521 and MZ-2531. No sound, or a RESET button that works only sometimes, often comes from these controls. Clean the control with contact cleaner. The pocket flap itself breaks easily; a 3D-printable guard has been published to protect it.

Floppy drives

• Sharp's drives turn at 300 rpm ±2.5%. The spindle is direct drive and the heads are moved by a stepping motor on a needle (lead) screw, so there is no belt. Slow or failed seeks point to the head carriage; see Floppy Drive Repair.
• If disks are read from the wrong drive, check whether E was held at start-up, which swaps the internal and external drive numbers.
• On an MZ-2520, software that relies on the drive swap circuit, such as Laydock, will not start, because that model does not have it. This is not a fault.
• The drives are tall and fairly noisy by design.

Voice recorder

• To check the deck with a known tape, hold C while the IPL starts to boot from it whatever the mode.
• Fast-forward or rewind of a C-60 should take no more than 130 seconds, and the tape speed should be within ±2.0%. A slow wind points to the mechanism; clean the heads, capstan and pinch roller.
• The pinch rollers on Sharp's earlier MZ-2000 deck and the MZ-1T02 data recorder are known to melt with age; check the MZ-2500's roller for the same.

Clock

The calendar clock is backed by a battery. A clock that loses the date when the machine is switched off points to that battery. Find it, check it and the board around it for leakage, and replace it with the same type; see Battery Explosion, Capacitor or Corrosion Damage if it has leaked.

Expansion boards

The two expansion slots come from the optional MZ-1U09 frame. Ohishi found that the slots are joined by a flat cable with the interrupt enable input wired to both in parallel, so only one board at a time can use daisy-chained interrupts. If a second board stops an otherwise working board, try each on its own.

Related pages

• Sharp MZ-2500
• Sharp MZ-2500 General Maintenance
• Sharp MZ-2500 Capacitor Replacement Guide
• Capacitor Failure Symptoms