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Sharp X68000 PRO General Maintenance

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Sharp X68000 PRO-HD with FM Towns II (htomari)
A black X68000 PRO-HD (bottom) with two FM Towns II machines on top (photo: htomari, CC BY-SA 2.0)

The Sharp X68000 PRO (CZ-652C, CZ-662C) and PRO II (CZ-653C, CZ-663C) are the desktop X68000s of 1989 and 1990.[1] Their power supplies differ from each other and from the tower models' SH4, and Sharp's reissued service manual covers only the XVI, so most of what follows comes from owners' repair notes.[2][3]

Before you start

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  • The PRO's supply is built for Japanese 100 V mains.[4] In countries with 220 to 240 V mains, use a step-down transformer and check its output before connecting the computer.
  • The PRO and PRO II have no main switch on the rear; the front switch is the only power switch.[5] Sharp's manuals for the tower models ask for at least 10 seconds between switching off and switching on again.[6][7]
  • Treat the supply's primary side as live after unplugging. The SH4 of the tower models holds more than 100 V DC on its primary side after the plug is pulled.[8]

Power supply

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Check which supply your machine has before buying parts. The PRO normally has the boxed PRO-BOX (UADP-0070CEZZ) and the PRO II the SH5, which is laid out like the tower models' supply, but mattsoft notes that some PROs have the tower-style supply.[4][9][2]

  • PRO-BOX: early and late versions differ in some capacitors and resistors. The board is paper-based epoxy with thin copper and needs care when desoldering, and its trimmer should not be turned.[10] leaded-solder's replacement board, which keeps the original case and harness, is an alternative to recapping.[4]
  • SH5: Poe gives R5 as 0.33 Ω and R36 as 220 Ω.[10] Kunichiko has published in-circuit resistance readings from a working SH5 for comparison.[2]
  • Harness: leaded-solder found the original wiring of a PRO's supply corroded. Replace any wire that has turned green or brittle.[4]

See the Sharp X68000 PRO Capacitor Replacement Guide.

Floppy drives

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The PRO and PRO II use TEAC FD-55GFR drives in a Sharp mounting, CMECF0015CE01, not the drive fitted to the tower models.[10] Poe lists nine electrolytics across the drive's control, eject and spindle motor boards; two of them, C23 and C25, are bipolar.[10] See the capacitor guide and Floppy Drive Repair.

Memory settings and backup cell

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The 16 KB SRAM holds the memory switch settings and is kept alive by a backup cell.[5] On the PRO-series machines a design problem around the SRAM can corrupt its contents even in normal use.[5] The clearing method is on the Troubleshooting Guide. Poe lists a Sony CR2450 among the PRO II's parts; if the settings are lost every time the machine is unplugged, check that cell first.[10]

Expansion

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The PRO and PRO II have four I/O slots.[5] Their circuits differ in places from the tower models, and some add-on hardware does not work with them: the Mach-2 SCSI board and Sharp's CZ-6EB1 expansion I/O box are listed as unsupported.[5] Check compatibility before fitting a board.

Case cleaning

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Sharp's manuals for the original X68000 and the XVI both say to wipe the case with a soft cloth dampened with water or a mild neutral detergent, and never to use benzine or thinner.[6][7]

Checklist

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  1. Confirm the mains supply is 100 V.
  2. Open the supply, identify it (PRO-BOX or tower-style), and recap or replace it.[9]
  3. Replace corroded harness wires.[4]
  4. Recap both floppy drives.[10]
  5. Clear and re-enter the SRAM settings, and on the PRO II check the CR2450 cell.[5][10]
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References

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  1. ↑ X68000, IPSJ Computer Museum, Information Processing Society of Japan—link(accessed 2026-10-21) Series table: PRO CZ-652C and PRO-HD CZ-662C with the March 1989 models; PRO II CZ-653C and PRO II-HD CZ-663C, April 1990.
  2. ↑ 2.0 2.1 2.2 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) PRO PRO-BOX, PRO II SH5, towers SH4. In-circuit resistance maps from the author's working SH5 (PRO II).
  3. ↑ 復刻サービスマニュアルX68000, Sharp, COCORO BOOKS—link(accessed 2026-10-21) The series holds one title, the service manual for the X68000 CZ-634C/CZ-644C (XVI).
  4. ↑ 4.0 4.1 4.2 4.3 4.4 x68000-pro-picopsu– leaded-solder, 2021—link(accessed 2026-10-21) Replacement board for the PRO (CZ-652C) supply UADP-0070CEZZ, fitting the original case and using the original harness; the original supports only Japanese 100 V; the PRO2 supply has the tower machines' layout; the original harness is often corroded, and green or crunchy wire should be replaced.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 5.5 X68000, Wikipedia (Japanese)—link(accessed 2026-10-21) No rear main power switch on the Compact, PRO and PRO II; 16 KB battery-backed SRAM for the memory switch settings, write-protected in normal use, but on the PRO-series machines a design problem around the SRAM can corrupt its data in normal use; PRO series with four expansion I/O slots, circuit design differing in places from the towers, some hardware such as the Mach-2 SCSI board unsupported; CZ-6EB1 expansion I/O box not compatible with the PRO and PRO II.
  6. ↑ 6.0 6.1 Sharp, X68000 取扱説明書 for the CZ-600C (File:Sharp X68000 CZ-600C Owner's Manual.pdf), 4.2 and 4.3, printed pages 19 and 20 (PDF pages 33 and 34): soft cloth with water or neutral detergent, no benzine or thinner; at least 10 seconds between off and on.
  7. ↑ 7.0 7.1 Sharp, X68000 XVI・XVI HD 取扱説明書 (File:Sharp X68000 XVI Owner's Manual.pdf), 4.2, printed page 23 (PDF page 39): soft cloth with water or diluted neutral detergent, no benzine or thinner; 4.3, printed page 24 (PDF page 40): 10 seconds or more between off and on.
  8. ↑ X68kXVI HDの電源リペア– Fram, 2015-05-23—link(accessed 2026-10-21) The SH4's primary side holds more than 100 V DC after the plug is pulled.
  9. ↑ 9.0 9.1 X68K_Pico_PSU_v2– mattsoft—link(accessed 2026-10-21) Some X68000 PROs have the tower-style ("Tetris") supply; open the PRO's supply first to see which type it has.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 SHARP X68000 修理– Poe—link(accessed 2026-10-21) PRO "PRO-BOX" supply: early (three- or four-digit serial) and late (five-digit) versions differ in some capacitors and resistors; paper-epoxy board with thin copper, take care; do not turn the VR. PRO II SH5: R5 0.33 Ω, R36 220 Ω. PRO II parts include a Sony CR2450 cell. PRO and PRO II floppy drive TEAC FD-55GFR, mounting CMECF0015CE01, separate from the ACE to X68030 drive CMECF0013CE01; nine capacitors listed, C23 and C25 6.8 µF 50 V bipolar.


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