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Sharp X68030 Troubleshooting Guide

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Sharp X68030 and X68000 Expert
An X68030 (left) beside an X68000 EXPERT. The X68030's drive tower is on the left with the two drive slots and EJECT buttons; the POWER, TIMER and HD BUSY lamps are at the top of the right-hand tower (photo: Manupkp, CC BY-SA 4.0)

Fault-finding on the Sharp X68030 (CZ-500C and CZ-510C) usually starts with the power supply, then the memory backup cell, the floppy drives and the SCSI hardware. Sharp's circuit diagrams for the machine are hosted here as the Sharp X68030 Schematic, and the part numbers below come from them. The supply is the SH4 type also fitted to the X68000 EXPERT, SUPER and XVI, so repair reports for those models' supplies are used below where they apply; each is marked as such.[1]

Warning: the supply runs from 100 V mains, and its reservoir capacitor C9 (470 µF, 180 V) stays charged after the plug is pulled. Unplug the machine and measure across C9 before touching the primary side.[2][3]

Quick reference

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Symptoms, causes and actions
Symptom Probable cause Action
Nothing happens with either switch Rear main switch off, wrong mains voltage, fuse F1 blown, failed supply No power
Rear switch on, front POWER switch does nothing Standby section (T2, IC31) or the power switch circuit on the control board No power
Power comes on but the machine does not start SCSI connector board unplugged, low +5 V Power on but no start
One colour missing from the picture That channel of the RGB output stage Picture faults
Settings and clock lost after the machine is unplugged Backup cell Settings and clock lost
An X68000 program crashes or runs too fast Not a fault: the program needs a patch or a slower start-up mode Software that will not run
Floppy drive will not read Dust and rust round the head motor, leaking capacitors Floppy drive faults
Floppy drive does not lock the disc Wheel board or index sensor Floppy drive faults
Internal hard disk not found Wrong ID on the rear switch; no internal cable on a CZ-500C Hard disk and SCSI
No sound Audio supplies or capacitors on the control board Sound faults

No power

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First checks

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  1. Check that the machine is on 100 V mains or a step-down transformer, and that the rear main switch is on. The tower models have both a rear main switch and a front POWER switch.[2][4]
  2. Check fuse F1 (125 V, 4 A) in the supply. A blown fuse means a fault in the supply; do not replace it and try again until you have found the cause.[2][3]
  3. The front POWER switch is a low-voltage switch on the control board, run from the standby rail VCC2. If the rear switch is on and the front switch does nothing, measure VCC2 at pin A5 of the supply's connector A. VCC2 comes from a separate small converter round transformer T2, with regulator IC31 (µPC78M05HF).[2][5]
  4. If VCC2 is present, check the other rails at connector A (A1 +5 V, A3 +12 V, A4 −12 V) with the machine switched on. If VCC2 is missing, the fault is in the standby section of the supply.[2]

Inside the supply

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The SH4's usual failure starts with leaking electrolytic capacitors. In Fram's XVI supply the electrolyte, which conducts, shorted the board round a zener diode, R33 and R34 and a transistor; the power transistor below them burst, and the fuse blew.[3] On the X68030 schematic, R33 and R34 are part of the T2 standby converter, with Q31 (2SC2333), Q32 (2SC1815), zener ZD31 (HZS7B-1L), R31 (220 kΩ) and C31.[2] Kunihiko Ohnaka recommends replacing leaking capacitors first, and warns that an open transformer winding or a shorted transistor will not show from outside.[1]

  1. Remove the supply, discharge C9, and look for leaked electrolyte and burnt board, especially round R33, R34 and ZD31.[2][3]
  2. Compare resistances measured on the solder side with Ohnaka's in-circuit readings, which he took on an X68030's supply. A reading far from his points to a failed part nearby.[1]
  3. Ohnaka traced a dead PRO II supply (the SH5, which uses the same designators in this section) this way: the reading across R31 (220 kΩ) should have been about 175 kΩ and was about 10 Ω. R31 itself was good; Q31 and Q32 had both failed short and the fuse had blown.[1]
  4. Replace C27, C28 and C31 by the board silkscreen, not by the schematic. Fram found that the XVI service manual's schematic draws those three the wrong way round, and the X68030 schematic shows C27 and C28 with their + ends towards the −12 V rail.[6][2]
  5. Fit replacement semiconductors so that their legs are not stressed. Fram's replacement ZD31, a 1 W part with stiff legs bent at the body, cracked and failed again.[6]
  6. The SH4 turns its outputs on when its main switch is on, so it can be tested out of the machine. Fram's outputs were unsteady straight after the repair and steady when he checked again later.[3]

Some parts in the supply are no longer made. Owners repairing XVI supplies of the same type have used these substitutes:[7]

Supply parts named on the X68030 schematic, with substitutes used on SH4 supplies
Ref Original part Substitute reported Notes
IC22 SI-3122V (12 V low-dropout regulator, TO-3P) BAJ2DD0T TO-220FP case with a different pin order; Makoto Kamada fitted one and photographed it
D23 5DL2CZ41A 10DL2CZ47A Higher-rated part in the same family
D32 11EFS2 (200 V 1 A fast recovery) ERA32-02V1 (200 V 1 A), AL01Z, D1NL20U Several 200 V 1 A fast-recovery diodes

Poe's notes record that on some CZ-500C supplies D27 is a two-lead part of unknown type, in which case J23 is changed to J19.[8]

If the original supply is beyond repair, Mashiron's ATX cable and AC adapter conversion sets, sold by BEEP, list the CZ-500C and CZ-510C among the models they fit.[9] The circle that makes the PSU SH-X replacement board says the X680x0 supplies are weaker than expected, with even the XVI assumed to draw 42 W, and built its board for over 100 W to suit machines with modern expansion boards and accelerators.[10]

Power on but no start

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  • The X68030 does not start if the SCSI connector board is not connected. Check its 40-way flat cable first after any work inside.[11]
  • Measure +5 V at connector B on the main board's supply input; C17 and C18 (330 µF) sit on that input.[2][12]
  • Check that the MC68EC030 and, if fitted, the MC68882 are seated in their sockets. A replacement CPU with an MMU is reported on the start-up screen.[4][12]

Picture faults

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The red, green and blue signals leave the main board's IC78 (CXA1260Q-Z) and pass through the analogue board to the 15-pin display connector. On the analogue board each colour has a 2SC1815Y buffer (Q401 to Q403), a 220 Ω preset (VR401 to VR403), a 75 Ω series resistor and a 470 µF output capacitor (C402 to C404).[12][13] If one colour is missing or weak, compare that channel's parts with the other two. The presets set the output levels, so note their positions before touching them.[13]

Settings and clock lost

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The memory switch settings and boot device are in a 16 KB SRAM backed up from a cell on the control board, which also runs the RF5C15 clock.[14][5] If the settings are lost whenever the machine is unplugged, the cell is flat or failing.

  1. Inspect the cell, marked BATT, and the board round it for leakage.[5] If it has leaked, see Battery Explosion, Capacitor or Corrosion Damage.
  2. The cell is charged from VCC2 through R205 (1 kΩ), R204 (2.4 kΩ) and D206, so check that VCC2 is present with the rear switch on.[5]
  3. Replace the cell with a rechargeable part of the right voltage, or remove the charging path before fitting a primary lithium cell.[5]
  4. Initialise the SRAM and set the memory switch again with SWITCH.X.[3]

Software that will not run

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These are not hardware faults.

  • Many programs written for the 68000 models need patches to run on the X68030.[4]
  • Holding XF3 at start-up makes the X68030 run at X68000 speed, and XF4 at XVI speed, by adding wait states; the CPU clock stays at 25 MHz and the clock register always reports 25 MHz.[14][4]
  • The MC68EC030 has no MMU. Operating systems that need one, such as NetBSD, need the CPU replaced with a full MC68030.[4][15]

Floppy drive faults

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Poe has photographed X68030 drives with rust on top of the spindle motor and with iron dust and ordinary dust at the root of the head motor's flexible cable. On the later drives he finds dust and rust cause more failures than leaking capacitors.[16]

  • Drive will not read: clean the head motor's cable root and the head mechanism, and inspect the capacitors under the spindle motor and on the motor driver board for leakage.[16]
  • Drive does not lock the disc after it is inserted: the wheel board or the index sensor has failed. Poe replaces the drive. Version 07 drives have parts that cannot be swapped from other versions.[16]
  • Drive reads badly after the motors were removed: the head position is set against the index timing. Do not remove the spindle or stepping motor just to change capacitors.[16]
  • An external X68000 drive needs a different cable, because the X68030's external floppy connector is a 40-pin half-pitch type instead of the X68000's 37-pin D-sub.[17]

See also Floppy Drive Repair.

Hard disk and SCSI

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  • The CZ-500C has no internal hard disk and no internal cable for one; only the CZ-510C has the cable.[11]
  • The rotary switch on the rear SCSI board sets the ID of the internal disk, which reads it through the 40-way flat cable; those lines are not connected on the computer's side of the cable. If the internal disk is not found, check that the switch has not been moved.[18][19]
  • The external SCSI connector is a 50-way half-pitch type. The SCSI board carries the 330/220 Ω terminating networks and a 1 A fuse on the power line it supplies.[11][20]
  • A SCSI-to-SD adapter can replace the internal disk. buffi used one with a ready-made SxSI disk image, and with SWITCH.X left at its defaults it worked straight away.[21]

See also Hard Drive Maintenance and Repair.

Sound faults

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The FM sound comes from the YM2151 (IC211) through the YM3012 DAC (IC217); the ADPCM sound comes from the MSM6258 (IC212). Both pass through MC3403 op-amp filters (IC229 and IC218) on the control board, and an NJM2073 amplifier (IC213) drives the headphone socket through the volume control.[5]

  1. Check the audio supplies VCC3′ and VCC4′, which come through chokes L203 and L202 (10 µH), and the capacitors on them (C225, C235, C240 and C258, all 100 µF 16 V).[5]
  2. Check the 100 µF capacitors round the headphone amplifier (C209, C210, C213 and C215) if only the headphone output is affected.[5]
  3. The full list of control board electrolytics is in the capacitor guide.
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References

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  1. ↑ 1.0 1.1 1.2 1.3 X68000シリーズ電源のハンダ面から見た抵抗配置図– Kunihiko Ohnaka (kunichiko), 2020-10-10—link(accessed 2026-10-21) SH4 supply in the EXPERT, EXPERT II, SUPER, XVI and X68030; SH5 in the PRO II. Solder-side resistor maps and in-circuit resistances measured on an X68030's SH4. Start by replacing leaking electrolytics; open transformer windings and failed transistors do not show. PRO II SH5 repair: burnt area round ZD31; across R31 (220 kΩ) a good supply reads about 175 kΩ, this one about 10 Ω; R31 tested good when removed; Q31 and Q32 had failed short and the fuse had blown; T2 tested good.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Sharp, power supply basic wiring diagram (電源部基本配線図), board UADP-0069CEZZ, in the X68030 schematic set reproduced in 桑野雅彦 (Kuwano Masahiko), X68030 Inside/Out, SoftBank, 1994. See Sharp X68030 Schematic (File:Sharp X68030 Schematic (X68030 Inside Out, 1994).pdf, PDF page 19). AC 100 V input; fuse F1 125 V 4 A; C9 470 µF 180 V; IC22 SI3122V (+12 V); IC23 µPC78M12HF (output to ground, common to −12 V); D23 5DL2CZ41A/F5KFU20/5CH25M; D27 FMB-33S/FMB-34S; D32 11EFS2; T2 standby converter with Q31 2SC2333, Q32 2SC1815, ZD31 HZS7B-1L, R31 220 kΩ, R33 and R34 100 Ω, C31 100 µF 10 V, and IC31 µPC78M05HF for VCC2; C27 and C28 drawn with + towards the −12 V rail; connectors A (A1 +5 V, A2 GND, A3 +12 V, A4 −12 V, A5 VCC2, A6 P.C) and B (B1 +5 V, B2 GND).
  3. ↑ 3.0 3.1 3.2 3.3 3.4 3.5 X68kXVI HDの電源リペア– Fram, 2015-05-24—link(accessed 2026-10-21) The primary side holds more than 100 V DC after the plug is pulled. Leaking "Long Life" capacitors; the conductive electrolyte shorted the zener diode, R33/R34 and a transistor; the power transistor below them burst and the fuse blew. The supply turns its outputs on when its main switch is on, so it can be tested alone; outputs unsteady at first, steady when rechecked. After renewing the backup cell: SRAM initialised, boot menu installed and defaults set with SWITCH.X.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 X68000, Wikipedia (Japanese)—link(accessed 2026-10-21) Rear main power switch and front switch on all but the Compact, PRO and PRO II. X68030: socketed MC68EC030 that can be replaced by a faster part or an MC68030 with MMU, which the start-up screen then reports; XF3, XF4 or XF5 held at start-up selects 10, 16 or 25 MHz operation; many X68000 programs needed patches to run; NetBSD and other Unix-like systems were ported for X68030s fitted with an MC68030.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 Sharp, control board basic wiring diagram (コントロール基本配線図), board DUNTK7930DE01, in the X68030 schematic set. File:Sharp X68030 Schematic (X68030 Inside Out, 1994).pdf, PDF page 11. Power switch SW-P0351CE and its logic on VCC2; backup cell BATT charged from VCC2 through R205 (1 kΩ), R204 (2.4 kΩ) and D206 (MA716), feeding VBT and the RF5C15 clock IC205; IC211 YM2151, IC217 YM3012, IC212 MSM6258, IC229 and IC218 MC3403, IC213 NJM2073 with C209, C210, C213 and C215 (100 µF 6.3 V); audio supplies VCC3′ and VCC4′ through L203 and L202 (10 µH) with C225, C235, C240 and C258 (100 µF 16 V).
  6. ↑ 6.0 6.1 【訂正】X68kの電源ユニットのシルク印刷に間違いがあった件&X68kの電源修理再び(未完)3– Fram, 2024—link(accessed 2026-10-21) The SH4 silkscreen is correct and the service manual schematic draws C31, C27 and C28 with reversed polarity. A replacement ZD31, a 1 W part with thick stiff legs bent at the body, had been damaged by the stress and failed again.
  7. ↑ X68000 XVI > 電源基板 > IC関連のリンク– 7of9, 2018-11-11—link(accessed 2026-10-21) IC22 SI-3122V (30 V in, 12 V out, 2 A, TO-3P), out of stock; substitute BAJ2DD0T in a TO-220FP case with a different pin order, fitted by Makoto Kamada; IC23 µPC78M12HF; Q31 2SC2333; D23 5DL2CZ41A, with 10DL2CZ47A available; Q51 2SC2655; Q32, Q33, Q53 2SC1815; D32 11EFS2 (200 V 1 A fast recovery), substitutes AL01Z, D1NL20U-5060 and ERA32-02V1 (200 V 1 A).
  8. ↑ SHARP X68000 修理– Poe—link(accessed 2026-10-21) Power supply table: CZ-500C and CZ-510C X68030 with the SH4, where D27 is sometimes a two-lead part of unknown type, in which case J23 is changed to J19.
  9. ↑ [TB60EB] SHARP X68000用ACアダプタ化セット EXPERT/SUPER/XVI/030用, BEEP—link(accessed 2026-10-21) Compatible models include the CZ-500C X68030 and CZ-510C X68030-HD.
  10. ↑ X68000の電源が100W超に大容量化できる改造キット– 鈴鹿廻, ASCII, 2024-03-14—link(accessed 2026-10-21) PSU SH-X kit for the X680x0 series; the circle says the X680x0 supplies are weaker than expected, with even the XVI assumed to draw 42 W, and built the kit for over 100 W to suit boards such as Raspberry Pi expansions and accelerators.
  11. ↑ 11.0 11.1 11.2 X68030 SCSI Adventure Part 1– buffi, 2025-02-17—link(accessed 2026-10-21) CZ-500C: no cabling for an internal hard disk (the CZ-510C has it); 40-pin flat cable to the SCSI I/O board; the board has the ID switch, a 330/220 Ω terminating network, capacitors and a 1 A fuse for the external power; the machine does not start without the SCSI board connected; external connector half-pitch 50-way.
  12. ↑ 12.0 12.1 12.2 Sharp, main board basic wiring diagrams (メイン基本配線図) (3), (4) and (6), in the X68030 schematic set. File:Sharp X68030 Schematic (X68030 Inside Out, 1994).pdf, PDF pages 4, 5 and 7. +5 V input B1/B2 with C17 and C18 (330 µF 6.3 V); IC42 MC68EC030 and IC43 MC68882-25 (option); IC78 CXA1260Q-Z with outputs ROUT, GOUT and BOUT.
  13. ↑ 13.0 13.1 Sharp, analogue board basic wiring diagram (アナログ基本配線図), board DUNTK7931DE01, in the X68030 schematic set. File:Sharp X68030 Schematic (X68030 Inside Out, 1994).pdf, PDF page 14. R, G and B buffers Q401 to Q403 (2SC1815Y) with presets VR401 to VR403 (220 Ω), series resistors R408, R407 and R405 (75 Ω) and output capacitors C402 to C404 (470 µF 6.3 V) to the 15-pin connector.
  14. ↑ 14.0 14.1 Kuwano, X68030 Inside/Out, pp. 108 and 109: XF3 at start-up sets the wait port to $0A (X68000 speed), XF4 to $04 (XVI speed); the CPU and clock port always reads $DC (68030, 25 MHz); the 16 KB SRAM at $ED0000 to $ED3FFF holds the memory switch settings and boot device and is kept by backup power.
  15. ↑ SHARP X680x0– DEKO—link(accessed 2026-10-21) NetBSD/x68k needs an MPU with an MMU on the X68030.
  16. ↑ 16.0 16.1 16.2 16.3 SHARP X68000 FDD K61432-71 K61432-72 K-61435-72 修理– Poe, 2020-02-23—link(accessed 2026-10-21) Photographs of X68030 CZ-500C drives: rust on the spindle motor; iron dust and dust at the root of the head motor's flexible cable, where rust progresses; on later drives, dust and rust cause more failures than leaking capacitors. Capacitors under the spindle motor and on the motor driver board found leaking. A drive that no longer locks the disc has a faulty wheel board or index sensor and needs replacing; version 07 parts have no substitute. Do not remove the spindle or stepping motor just to change capacitors, because head adjustment depends on the index timing.
  17. ↑ Kuwano, X68030 Inside/Out, pp. 19 and 20: external floppy connector changed from a 37-pin D-sub on the X68000 to a 40-pin half-pitch connector on the X68030.
  18. ↑ Kuwano, X68030 Inside/Out, p. 16: the internal hard disk's ID is set by a rotary switch on the hard disk connector board; the control board, the connector board and the disk are joined by a 40-way flat cable, the disk reads three of its lines as ID lines, and the control board leaves them unconnected. Internet Archive item X68030InsideOut1994.
  19. ↑ X68030 SCSI Adventure Part 3– buffi, 2025-02-18—link(accessed 2026-10-21) The rear ID switch connects to pins 1 to 3 of the HC connector, which go nowhere on the board side.
  20. ↑ Sharp, I/O, FD connector, SCSI connector and LED basic wiring diagram, in the X68030 schematic set. File:Sharp X68030 Schematic (X68030 Inside Out, 1994).pdf, PDF pages 16 and 18. SCSI connector board DUNTK7933DE01 with the ID switch, terminator networks RM601 and RM602 (220/330 Ω) and fuse F601.
  21. ↑ X68030 SCSI Adventure Part 2– buffi, 2025-02-17—link(accessed 2026-10-21) Internal SCSI-to-SD adapter (Henkan Banchou Pro) loaded with the SxSI-SCSI HDD image v3.01; SWITCH.X needed no changes; it worked once the cable was connected.


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