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Sharp X1 Turbo Z Troubleshooting Guide

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Sharp X1turbo Z II CZ-881C front with door open
X1turbo Z II with the front door open, showing the reset buttons and mode switches (photo: Jun Sasaki, AKIBA PC Hotline!, copyright Impress Corporation)

Fault finding on the Sharp X1turbo Z series (CZ-880C, CZ-881C and CZ-888C). No Sharp service manual or schematic for these models was found. The checks below come from Sharp's CZ-880C owner's manual, X1 Center's surveys and the Sharp Museum's repairs of X1-family machines. Inside-the-case work is described on Sharp X1 Turbo Z General Maintenance.

What a working X1turbo Z does

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  1. Switch on the rear main power switch, then the front power switch.[1]
  2. The IPL tries to start a program from the disk type set by the disk mode switch. If nothing starts it shows "Make your device ready" and "Press selected key to start driving", with F (floppy), R (ROM), C (CMT, the data recorder) and T (timer).[2][3]
  3. With the supplied system disk, Disk BASIC starts.[4]

First checks

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  • Several switches sit behind the front door: the start-up disk type switch (2D or 2HD), the VTR record mode switch, the 200-line automatic switching stop switch (WIDTH and DEFCHR) and the standard/high-resolution switch. Check them before suspecting a fault.[5]
  • The disk mode DIP switch on the back must be set for the disks you use. Sharp ships it so that the front start-up disk type switch decides.[3] The settings are in the maintenance guide.
  • The front power switch does not turn the computer fully off. The television control and timer stay powered until the rear main power switch is turned off.[1]
  • Leave at least 10 seconds between switching off and switching on again.[1]

Keyboard does not respond or behaves oddly

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  • If the keyboard was plugged in while the main power switch was on, leave it plugged in, turn the main power switch off and turn it on again.[1]
  • The computer has keyboard connectors at the front and the back. Only one keyboard can be used at a time.[5]
  • Keys that work only while the plug is pressed one way point to cracked solder joints on the keyboard connector inside the computer. X1 Center lists this as a common fault on the turbo Z series as well as the earlier X1 models.[6]

Picture wrong

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  • The display mode is set by the standard/high-resolution switch whenever the computer is reset with the IPL or NMI button, switched on, sent the BASIC command BOOT, or given a WIDTH command. Set the switch to suit the display before doing any of these.[5]
  • Older X1 games that start from the IPL can make the picture roll on a high-resolution display. The IPL sets the high-resolution mode, then the game sets the standard mode again. The 200-line automatic switching stop switch (W/D switch) blocks the game's access to the CRT controller and the PCG. It works only with programs that define their characters (DEFCHR$) and set the screen (WIDTH) when they start. Sharp's method for a game that does not use the PCG is:[7]
    1. Set the W/D switch to NORMAL and the standard/high-resolution switch to HIGH.
    2. Hold SHIFT and BREAK and press the IPL reset button. When the IPL menu appears, press M to start the machine-code monitor.
    3. Choose the screen width the game uses (40 or 80 characters) from the monitor, as the manual describes. If you do not know which it uses, try both.
    4. Put the game disk in, set the W/D switch to CUT and press the IPL reset button.
    5. Once the game has started, set the W/D switch back to NORMAL.
For a game that loads its own characters into the PCG, Sharp's manual adds a first stage: start the game with the standard/high-resolution switch at STANDARD, let it load even though the picture rolls, and set the switch to HIGH once the game has started. Do not use the power switch in place of the IPL reset button afterwards, because it clears the PCG.[7]
  • The IPL reset button resets the CPU, the 8255, PSG, CTC, SIO, CRT controller, floppy controller and display control port, and restarts the IPL from ROM. The NMI button sends a non-maskable interrupt, which jumps to address 0066H in ROM or RAM, whichever was being used.[2]
  • The video output level and hue adjusters on the back change only the composite video output, and Sharp tells owners to have the dealer adjust them.[5]

Floppy drive faults

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  • Disks do not boot although the drive runs: check the disk mode DIP switch and the start-up disk type switch against the disk's type.[3][5]
  • An external drive gives errors or the drives clash: the external drives must be numbered 2 and 3, because the internal drives are 0 and 1. Running two drives with the same number can damage them.[8]
  • A 2DD disk will not read: the 2D/2DD signal to the internal drives follows DIP switch 6 only, and software cannot change it.[9][3]
  • Loud grinding at boot or on disk access: on an X1turbo, the Sharp Museum traced this to a failed track 0 sensor in the drive, so that the drive kept trying to step the head past track 0. The museum could not find a matching replacement sensor.[10]
  • Never move a drive's front lever while its lamp is lit, because the head is on the disk.[11]

Clock faults

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If the clock does not run, the Sharp Museum's experience on the X1turbo applies: the calendar clock's 32.768 kHz crystal has a trimmer capacitor to ground, and ageing of the trimmer stops the oscillator. Turning the trimmer slightly with a fine screwdriver brings it back. The museum notes that even the last model, the X1turbo Z III, keeps a trimmer in this circuit.[10] The X1turbo Z and Z II use a µPD1990AC clock chip and the Z III a µPD4990.[12] If the clock runs but forgets the time when the main power is off, check the nickel-cadmium backup cell, which can also leak; see clock backup battery.[13][14]

Computer completely dead

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  1. Check that the rear main power switch is on as well as the front power switch.[1]
  2. The Sharp Museum, which owns X1-family machines from the first X1 to the X1turbo Z III, has not had a power unit fail on any of them.[10]
  3. On an X1turbo, the museum traced a completely dead machine to ageing electrolytic capacitors on the superimpose (telopper) board, which loaded the 12 V supply until its protection shut down. The test and the capacitors are described in the X1turbo troubleshooting guide.[10] The X1turbo Z also has a digital telopper; on the Z III it is on a separate board below the main board.[15][16] Whether the X1turbo Z's board fails in the same way is not recorded.
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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 Sharp Corporation, X1turboZ CZ-880C 取扱説明書 (owner's manual, Japanese, December 1986), page 31: leave at least 10 seconds between switching off and on; with the display television, turn on the rear main power switch first, then the front power switch; plugging in the keyboard with the main power switch on can cause malfunction, in which case leave it plugged in and turn the main power switch off and on again; the front power switch leaves TV control by key and the timer working; turn the rear main power switch off to cut power completely. Hosted as Sharp X1turbo Z CZ-880C Owner's Manual (Japanese).pdf.
  2. ↑ 2.0 2.1 X1turboZ CZ-880C 取扱説明書, pages 80 and 81: pressing the IPL reset switch resets the CPU, 8255 (printer and others), PSG, CTC, SIO, CRTC, FDC and display control port (1FDX), switches the main memory bank to ROM and starts the IPL from address 0000H of the ROM; pressing the NMI switch sends an NMI to the Z80A, which jumps to address 0066H in RAM or ROM according to the ROM/RAM switching flip-flop; the IPL screen reads "Make your device ready", "Press selected key to start driving:", "F:Floppy", "R:ROM", "C:CMT", "T:Timer"; holding SHIFT and BREAK while pressing the IPL reset switch and then pressing M at the IPL screen starts the machine-code monitor, which shows a * prompt.
  3. ↑ 3.0 3.1 3.2 3.3 X1turboZ CZ-880C 取扱説明書, page 79: the initial disk drive setting at power-on is made by the DIP switch on the back; shipped set so that the front start-up disk type switch takes priority.
  4. ↑ X1turboZ CZ-880C 取扱説明書, page 11: the compatible mode is supported by BASIC CZ-8FB02.
  5. ↑ 5.0 5.1 5.2 5.3 5.4 X1turboZ CZ-880C 取扱説明書, pages 18 to 22: keyboard connectors at the front and the back, either may be used but not both at once; front door switches: start-up disk type (2HD or 2D), VTR record mode, 200-line automatic switching stop (set to CUT only when loading X1 IPL machine-code programs on a high-resolution display) and standard/high-resolution, whose setting decides the display mode when the IPL or NMI reset button is pressed, the power is switched on, BOOT is typed in BASIC or the BASIC WIDTH command is used; rear video level and hue adjusters for the computer picture at the video output, to be adjusted by the dealer.
  6. ↑ 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.
  7. ↑ 7.0 7.1 X1turboZ CZ-880C 取扱説明書, pages 80 to 82, use of the 200-line automatic switching stop switch (W/D SW): used to run IPL-start X1 machine-code software on a high-resolution display, and works only where the program runs DEFCHR$ and WIDTH at its start; on a high-resolution display, X1 IPL-start games set the CRTC to the standard display mode after the IPL has set the high-resolution mode, so the picture rolls; the W/D switch forcibly blocks access to the PCG and the CRTC; procedure for software without PCG: check whether the program is WIDTH 80 (640 × 200) or WIDTH 40 (320 × 200), set the W/D switch to NORMAL and the standard/high-resolution switch to HIGH, start the machine-code monitor with SHIFT + BREAK and the IPL reset switch, select WIDTH 40 or 80 in the monitor, set the disk and the W/D switch to CUT, press the IPL reset switch, then return the W/D switch to NORMAL; for software using the PCG: first set the W/D switch to NORMAL and the standard/high-resolution switch to STANDARD, switch on with the disk inserted and let the program load although the picture rolls, then set the switch to HIGH once the game has started, and continue as above; do not use the power switch in place of the IPL reset switch, as this clears the PCG contents.
  8. ↑ X1turboZ CZ-880C 取扱説明書, page 62: the internal drives and external drives are both numbered 0 and 1, so one pair must be changed to 2 and 3; if not, the system does not work properly and the drives may be damaged.
  9. ↑ 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-880C, CZ-881C, CZ-888C: the 2D/2DD switching signal to the internal drives changes with DIP switch 6 only and cannot be controlled or detected by software; it is not connected to the expansion connector.
  10. ↑ 10.0 10.1 10.2 10.3 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) None of about six machines from the mania-type X1 to the X1turbo Z III has had its power supply fail; a completely dead X1turbo can be caused by the telopper board's electrolytics overloading the 12 V supply; the RTC's 32.768 kHz crystal has C3 and C4 to ground, C4 being a trimmer whose ageing stops the oscillator, cured by turning it slightly; the last model, the X1turbo Z III, has the same circuit; loud grinding at boot or disk access is a failed track 0 sensor (photo coupler) in the drive, and no replacement part was found.
  11. ↑ X1turboZ CZ-880C 取扱説明書, page 40: never move the front lever while the drive motor is running (indicator lit), because the head is in contact with the disk and the disk may be destroyed.
  12. ↑ 搭載チップセット, X1 Center—link(accessed 2026-10-21) RTC: µPD1990AC on the CZ-880C and CZ-881C; µPD4990 on the CZ-888C.
  13. ↑ X1turboZ CZ-880C 取扱説明書, page 87: clock built in, backed up by a built-in nickel-cadmium cell.
  14. ↑ 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.
  15. ↑ X1turboZ3, シャープ博物館 (Sharp Museum)—link(accessed 2026-10-21) On the Z III, the brown board below the main board carries the digital telopper and front switch circuits.
  16. ↑ Oh!MZ, December 1986 (Nihon SoftBank), "速報 X1turbo Z": the X1turbo had a built-in digital telopper, and on the Z the 4096-colour computer picture can also be superimposed on television or video and recorded. Scan on the Internet Archive, item OhMZ198612X68000X6800X1turboZX.


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