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Sharp X68000 SUPER Troubleshooting Guide

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Sharp X68000 XVI power supply schematic (service manual)
Sharp's circuit diagram of the SH4 power supply from the X68000 XVI service manual; the SUPER uses the same board

Fault-finding on the Sharp X68000 SUPER (CZ-604C) and SUPER-HD (CZ-623C) starts with the SH4 power supply, which the SUPER shares with the Sharp X68000 XVI. Sharp's diagram of that supply, with the voltage on every output pin, is in the Sharp X68000 XVI Service Manual.[1][2] Poe, a Japanese repairer, has written up a SUPER that would not power on.[3]

Warning: the supply runs from 100 V mains and its primary side holds more than 100 V DC after the plug is pulled.[4]

Quick reference

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Symptoms, likely causes and where to look
Symptom Likely cause Section
Dead, no lamps Rear main switch off, no 100 V supply, blown fuse, leaking supply capacitors No power
Supply recapped but still dead Burnt parts, failed transistor, open transformer winding Still dead
Settings lost or wrong at start-up Flat or leaking backup cell, corrupt SRAM Settings
Disc will not eject or will not read Drive capacitors, grease, sensors Floppy drives

No power

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  1. Check the supply voltage. The X68000 series is built for 100 V Japanese mains.[5]
  2. Check the main switch on the rear. The tower models have it as well as the front switch, and Sharp's manuals say to turn it on first.[5][6]
  3. Take the supply out and check its fuse. On Sharp's diagram of the SH4 it is F1, 125 V 4 A.[2]
  4. Look for leaked electrolyte. In Poe's SUPER, C24, C27, C40, C41 and C42 had leaked heavily.[3] In Fram's SH4 from an XVI-HD the electrolyte had shorted the zener diode, R33, R34 and a transistor, a power transistor had burst and the fuse had blown.[4]
  5. Recap the supply; see the Sharp X68000 SUPER Capacitor Replacement Guide. Fit C27, C28 and C31 by the board's silkscreen, not by the service manual.[7]
  6. Test the supply on the bench. The SH4 switches its outputs on when its own main switch is on.[4] The pin-out of its connectors is tabled on the XVI capacitor guide.[2]

Supply still dead after a recap

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  • kunichiko notes that replacing the leaking capacitors, resoldering joints and replacing burnt or cracked parts often does not fix an X68000 supply, because open transformer windings and failed transistors do not show on inspection. He has published in-circuit resistance readings from the solder side of a working SH4 board for comparison.[1]
  • If the supply cannot be saved, Poe points out that firms repair these supplies and that adapter units are sold which let a PC/AT (ATX) supply be used.[3]

Settings and SRAM

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The 16 KB SRAM keeps the memory switch settings and depends on a backup cell.[5] Poe's SUPER notes include replacing it.[3] If the SRAM holds corrupt data, Poe gives this method with the debugger DB.X under Human68k:[8]

  1. Start Human68k and run db.
  2. Enter -mes e8e00d 31 to allow writes to the SRAM.
  3. Enter -mes ed0000 00 to clear the SRAM's program area.
  4. Enter -mes e8e00d 00 to protect the SRAM again.
  5. Enter -q to leave DB.X, then reset.

Some versions of DB.X did not accept these commands for Poe; the program SRAM_CLR.R clears the SRAM as well.[8]

Floppy drive faults

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  • From the ACE onwards a stuck disc is forced out from the front of the machine, where the original X68000 had a button on the rear.[5] On the XVI, Sharp says to hold the eject button for about three seconds or more when the button's lamp is out.[6]
  • Poe found capacitors leaking under the spindle motor and on the motor driver board of X68000 drives; the SUPER's drive capacitors are listed in the capacitor guide.[9][3]
  • Do not remove the spindle or stepping motor to reach a capacitor; the head position depends on them.[9]

See also Floppy Drive Repair.

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References

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  1. ↑ 1.0 1.1 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) SUPER and SUPER-HD use the SH4. Replacing leaking electrolytics, fixing solder joints and replacing burnt or cracked parts is often not enough; open transformer windings and failed transistors do not show on inspection. In-circuit resistance readings from a working SH4 board are given for comparison.
  2. ↑ 2.0 2.1 2.2 Sharp, service manual CZ-134 for the X68000 XVI (File:Sharp X68000 XVI Service Manual.pdf), 22, power supply basic wiring diagram, printed pages 97 and 98 (PDF page 85): SH4 board UADP-0069CEZZ, fuse F1 125 V 4 A, output connector pin-outs. See Sharp X68000 XVI Service Manual.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 SHARP X68000 SUPER / SUPER-HD CZ-604C CZ-623C 修理備忘録– Poe—link(accessed 2026-10-21) A SUPER that would not power on; repair including the power supply; battery replacement; C24, C27, C40, C41 and C42 in the SH4 had leaked heavily; firms repair these supplies, and units are sold that adapt a PC/AT (ATX) supply.
  4. ↑ 4.0 4.1 4.2 X68kXVI HDの電源リペア– Fram, 2015-05-23—link(accessed 2026-10-21) The primary side holds more than 100 V DC after unplugging. Leaking capacitors; electrolyte shorted the zener diode, R33/R34 and a transistor; the power transistor below them burst and the fuse had blown. The supply turns its outputs on when its own main switch is on, so it can be tested alone.
  5. ↑ 5.0 5.1 5.2 5.3 X68000, Wikipedia (Japanese)—link(accessed 2026-10-21) Power 100 V AC; the tower models have a main power switch on the rear; 16 KB battery-backed SRAM keeps the memory switch settings; the ACE (March 1988) added forced ejection of floppy discs from a front switch.
  6. ↑ 6.0 6.1 Sharp, X68000 XVI・XVI HD 取扱説明書 (File:Sharp X68000 XVI Owner's Manual.pdf), 4.3, printed page 24 (PDF page 40): rear main switch on before the front switch; 6.3, printed pages 46 and 47 (PDF pages 62 and 63): the eject button works while its lamp is lit, and holding it for about three seconds or more ejects the disc when the lamp is out.
  7. ↑ 【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, 2024-03-24—link(accessed 2026-10-21) The SH4 diagram draws C31, C27 and C28 with reversed polarity; the silkscreen is correct.
  8. ↑ 8.0 8.1 X68000 EXPERT CZ-602C CZ-612C / EXPERT II CZ-603C CZ-613C / FDDユニット K61432-72 修理備忘録– Poe—link(accessed 2026-10-21) X68000 SRAM initialisation with DB.X: db; -mes e8e00d 31; -mes ed0000 00; -mes e8e00d 00; -q; some versions of DB.X did not accept the commands; SRAM_CLR.R as an alternative.
  9. ↑ 9.0 9.1 SHARP X68000 FDD K61432-71 K61432-72 K-61435-72 修理– Poe, 2020-02-23—link(accessed 2026-10-21) Capacitors under the spindle motor and on the motor driver board found leaking; do not remove the spindle or stepping motor just to change capacitors.


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