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Sharp X1 Turbo General Maintenance

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Sharp X1turbo Model 10 and Model 30 interiors
X1turbo Model 10 (left) and Model 30 (right) with their covers off, fronts at the bottom (photo: Jun Sasaki, AKIBA PC Hotline!, copyright Impress Corporation)

These notes cover the Sharp X1turbo Model 10, 20 and 30 (CZ-850C, CZ-851C and CZ-852C). Sharp's owner's manual (取扱説明書) for these models was not found online; the BASIC user's manual is on the Internet Archive and refers readers to the owner's manual for handling.[1] Where Sharp's notes for the first X1 are used instead, the text says so. No Sharp service manual was found on the Internet Archive or X1 Center.

Safety

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The X1turbo has a mains power unit inside the case. On the Model 20 and 30 it supplies the boards with 5 V, +12 V and −12 V.[2] The Model 10 has its own power unit, which gives 13.8 V for the cassette deck in place of ±12 V.[3]

  • Switch off and unplug the mains lead before taking any screw out.
  • Do not touch the power unit's board until its capacitors have discharged; measure across the large capacitors first.
  • Sharp's warnings for the first X1 apply here as well: do not switch on with the cover removed, and do not leave screws or other metal inside.[4]

Everyday care

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Sharp's care notes for the first X1, on Sharp X1 General Maintenance, cover ventilation, damp, cleaning the case without solvents, leaving at least 10 seconds between switching off and on, and cleaning the cassette head monthly.[5] The X1turbo is larger and heavier than the first X1: 390 × 390 × 108 mm, and 7.3 kg (Model 10) to 10.9 kg (Model 30).[6]

Inside the case

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The Model 10's interior is simple, and AKIBA PC Hotline! notes that taking it apart to repair the cassette deck is easy.[7] On the Model 20 and 30 the boards are stacked:

  • The calendar clock chip is on the main board, completely hidden under the sub board, so the sub board has to come off to reach it.[8]
  • The superimpose (telopper) board sits behind floppy drive 1, in the same frame as the expansion slots. It is connected to the main board by four cables; the yellow and black pair is its power supply.[8]
  • The power unit's 12 V and −12 V outputs reach the sub board on connector A.[2]

No step-by-step disassembly procedure has been published. Photograph each board, cable and screw position before removing it, and keep screws from each stage separate.

Initial mode switch

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The DIP switch on the rear panel sets the type of disk the computer boots from. Sharp ships it with all switches on (disk type 0), which suits the built-in drives.[1] Note the setting before cleaning or moving the machine, and set it back to all on if a disk will not boot.

Floppy drives (Model 20 and 30)

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The built-in drives are TEAC FD-54B-08 5¼-inch 2D drives (Sharp part DMECF0004CE01).[9] X1 Center's notes for anyone fitting a different drive:[9]

  • The FD-54B-08 does not move its head to track 0 at power-on.
  • The interface's external connector has 150 Ω terminators and expects a drive that restores itself at power-on. A drive without this feature can overrun its end stop badly the first time it is asked for a track other than track 0.
  • X1 Center lists the internal drive cable on the Model 20 and 30 as not replaceable.

Clock backup battery

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The Model 20 and 30 clock is backed up by a 2.4 V nickel-cadmium cell on the main board, charged through a diode and resistor.[2] Like the first X1's cell, it can leak and corrode the board around it. X1 Center found blackened, corroded plated holes around the cell on an X1turbo III sub board, and the Sharp Museum removed the rechargeable cell from its X1turbo to stop it leaking.[10][8] If you keep the cell, inspect it each time the case is open; X1 Center suggests a 5.5 V supercapacitor in its place if long backup is not needed.[10]

Keyboard

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  • The X1turbo keyboard's curly cord sheath turns white and crumbles with age. Replace a cracked cord, because the keyboard line carries +5 V. Remove the six screws under the keyboard, unplug the three-pin connector, and fit a new cable with a 3.5 mm stereo plug through the old cord bush, as described on Sharp X1 General Maintenance.[11]
  • A keyboard that works only while its plug is pressed one way has cracked solder joints on the keyboard connector in the computer; reflow them. X1 Center lists this among the commonest faults on the X1, turbo and Z series.[12]
  • The slide switch beside the keyboard selects mode A or mode B. Mode B changes the kana layout and allows several keys to be read at once, so check this switch before treating an odd kana layout as a fault.[13]

Superimpose (telopper) board

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The Model 20 and 30 superimpose board carries many electrolytic capacitors, and the Sharp Museum found that ageing ones on this board can load the 12 V supply until its protection shuts the computer down. If you do not use the telopper, the Sharp Museum's approach is to leave the board's power cable (the yellow and black wires) disconnected.[8] See Sharp X1 Turbo Capacitor Replacement Guide for the board's capacitors.

After any work

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  1. Check that no screws or offcuts are left inside, and refit every cover before switching on.
  2. Check the initial mode switch setting.
  3. Switch on. With no bootable disk or tape, the IPL shows its menu (floppy, ROM, cassette or timer).[1]
  4. Boot BASIC, check the clock with TIME$ and test both floppy drives.

Maintenance checklist

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Task When
Check the clock cell for leakage Whenever the case is open
Clean the floppy drive heads When disks fail to read, and before archiving disks
Inspect the keyboard cord Whenever the keyboard is handled
Check the superimpose board's capacitors If the computer will not start
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References

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  1. ↑ 1.0 1.1 1.2 Sharp Corporation, X1turbo CZ-850C/851C/852C ユーザーズマニュアル (user's manual, Japanese): the introduction asks readers to read the owner's manual (取扱説明書) first for correct use; page 56: the initial mode switch (DIP switch) sets the boot disk type and is set to all ON (disk type 0) at the factory; if no system program starts, the IPL shows "Make your device ready" with F (floppy), R (ROM), C (CMT) and T (timer), and the switch setting and drive state should be checked before switching on again. Scan on the Internet Archive, item sharp-cz-850-c-851-c-852-c-users-manual.
  2. ↑ 2.0 2.1 2.2 CZ-851C/852C(X1turbo)回路図(Oh!MZ誌), X1 Center—link(accessed 2026-10-21) Sub board power connector: A-1 GND, A-2 VCC3 (12 V), A-3 VCC4 (−12 V), AC-1 GND, AC-2 VCC1; main board: µPD1990AC clock with a 2.4 V cell (BAT0005CE) charged through D1 (1SS119) and R3 (3.3 kΩ).
  3. ↑ X1turbo model10, シャープ博物館 (Sharp Museum)—link(accessed 2026-10-21) The Model 10's power supply is specific to it and gives 13.8 V for the cassette in place of ±12 V.
  4. ↑ CZ-800C 取扱説明書, File:Sharp X1 CZ-800C Owner's Manual (Japanese).pdf, page 63 of the scan: do not switch on with the cover removed; do not leave screws or metal inside.
  5. ↑ Sharp Corporation, CZ-800C 取扱説明書 (owner's manual for the first X1), File:Sharp X1 CZ-800C Owner's Manual (Japanese).pdf, pages 10 and 11 of the scan: ventilation, damp, cleaning without solvents, at least 10 seconds between off and on, monthly cassette head cleaning.
  6. ↑ Oh!MZ, November 1984 (Nihon SoftBank), page 65: computer 390 × 390 × 108 mm; weight 7.3 kg (Model 10), 9.2 kg (Model 20), 10.9 kg (Model 30). Scan on the Internet Archive, item oh-mz-1984-12, file Oh!MZ_1984-11, leaf 66.
  7. ↑ ターボな走りが始まった「X1turbo」– 佐々木 潤 (Jun Sasaki), AKIBA PC Hotline! (Impress), 2018-08-28—link(accessed 2026-10-21) With the covers off, the Model 10's interior is simple, so taking it apart to repair the cassette deck is easy.
  8. ↑ 8.0 8.1 8.2 8.3 X1turboのよくある故障とその対処, シャープ博物館 (Sharp Museum)—link(accessed 2026-10-21) The telopper board is behind drive 1, in the same frame as the expansion slots, with four cables from the main board; the yellow and black wires are its power (12 V); its many electrolytics lose capacitance and overload the 12 V supply until the protection cuts it; disconnecting the board's supply lets the machine start, and the museum leaves it disconnected; the RTC (µPD1990) is on the main board, completely hidden by the sub board; the rechargeable cell on the museum's X1turbo has been removed to prevent leakage.
  9. ↑ 9.0 9.1 X1/turbo/Zシリーズ搭載FDDインターフェース仕様, X1 Center—link(accessed 2026-10-21) CZ-851C/852C: TEAC FD-54B-08, 5¼-inch 2D, step rate 6 ms, 1 kΩ terminator, no power-on restore, Sharp part DMECF0004CE01; external connector input terminators 150 Ω (−33 mA); internal FDD cable not replaceable; a 150 Ω interface assumes power-on restore, and a drive without it can overtrack badly when it first accesses a track other than track 0.
  10. ↑ 10.0 10.1 時計バックアップ用ニッカド電池, X1 Center—link(accessed 2026-10-21) The clock backup NiCd cell leaks and corrodes the board; on a CZ-870C (X1turbo III) sub board the vias under and beside the cell were black, and one track appeared broken; if backup is not needed, remove the cell or fit a 5.5 V supercapacitor.
  11. ↑ X1/turbo用キーボードケーブルの劣化と交換, X1 Center—link(accessed 2026-10-21) The X1 and X1turbo keyboard cord sheath whitens and crumbles; the keyboard line carries +5.0 V; six screws on the keyboard underside; three-pin connector; 3.5 mm plug; cord bush reusable.
  12. ↑ キーボードコネクタの半田剥離, X1 Center—link(accessed 2026-10-21) Keyboard connector solder cracks are a common fault on the X1, turbo and Z series; reflow the joints.
  13. ↑ X1 (コンピュータ), Japanese Wikipedia—link(accessed 2026-10-21) The X1turbo keyboard has an A/B mode slide switch; mode A is compatible with earlier models; mode B changes kana input to the syllabic layout and allows simultaneous key input.


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