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Sharp X1F Troubleshooting Guide

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Sharp X1F Model 10 rear panel
Rear panel of an X1F Model 10: power switch, RGB OUT, TV CONTROL, PRINTER, AUDIO OUT, two joystick ports and the KEY BOARD jack, with the I/O slots above (photo: AKIBA PC Hotline!, Impress)

The Sharp X1F has its mains power supply, main board and either a data recorder (Model 10, CZ-811C) or a 5¼-inch floppy drive (Model 20, CZ-812C) in one case, with a separate keyboard on a 3.5 mm plug.[1] Faults appear in the keyboard connection, the Model 10's tape deck, the Model 20's drive and the power supply.

Normal start-up

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At power-on the X1's IPL program tries to boot from the floppy drive, then from a ROM board in an expansion slot, then from the cassette. If none of them answers, or the user cancels, it shows a menu offering the three boot devices and the television timer editor.[1] The X1F has no BASIC in ROM: BASIC loads from tape on the Model 10 and from disk on the Model 20.[1][2] An IPL menu on the screen therefore shows that the CPU, IPL ROM, video and RGB output are working.

Symptom table

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X1F symptoms
Symptom Probable cause Action
Nothing at all, no indicators No mains at the supply, rear POWER switch off, or a failed power supply Check the mains lead and switch, then measure the supply outputs with the main board connector in place. See Sharp X1F Capacitor Replacement Guide.
Power indicator lit, no picture Monitor not in RGB mode, RGB cable, or a fault on the main board Try another RGB monitor and cable. The X1F has no composite video output; the X1G was the first X1 to have one.[3]
IPL menu appears, keyboard does nothing Keyboard plug in a cracked jack, damaged cord, or a keyboard fault Try the other keyboard jack; check +5 V on the jack; see Keyboard faults.
Software hangs after pressing reset The NMI reset was used; programs not written for it freeze Use the IPL reset button to restart the machine.[1]
Tape loads stop at once (Model 10) Tape end detected because the take-up drive or tape counter is not turning Check the rubber ring and counter belt; see General Maintenance.
Head does not load when the deck starts (Model 10) Loading belt melted or broken Replace the belt and clean off the residue.[4]
Disk does not boot (Model 20) Dirty heads, the wrong disk type, or a drive fault Clean the heads; check that the disk is a 2D disk; test the drive as in Floppy Drive Repair.

Keyboard faults

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The keyboard contains an 80C48 microcontroller that scans the keys and sends each key code to the 80C49 sub-CPU in the main unit over a single wire. Data goes one way only, from keyboard to computer.[5] The keyboard plug is a 3.5 mm stereo plug: +5 V on the tip, the data signal on the ring and ground on the sleeve.[6]

  1. Plug the keyboard into the other jack. The X1F has one at the rear and one on the left side of the front.[7]
  2. With the computer on and the keyboard unplugged, measure between tip and sleeve of each jack. Expect +5 V.[6]
  3. If a key works only while the plug is pushed one way, reflow the joints on the jack board. X1 Center lists cracked joints there as one of the most frequent faults across the X1, X1turbo and X1turboZ.[8]
  4. Check the cord. On X1 and X1turbo keyboards the sheath of the coiled cord perishes, and the bare cord carries +5 V.[9]
  5. If +5 V is present and the cord is sound, look at the keyboard's signal line with an oscilloscope while pressing a key. The signal idles high, and each key press sends a long low header followed by short low pulses whose spacing sets each bit.[6] No pulses point to the keyboard; pulses with no response point to the computer.

The X1 keyboard cannot report several keys pressed together, apart from Shift and the other modifier keys. This is how the serial keyboard works and is not a fault.[1]

Data recorder faults (Model 10)

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X1 Center's repair notes cover the decks of the first X1 and of the CZ-8RL1 recorder. On both, the failures that stop tape loading are in rubber parts:[4][10]

  • The head does not move onto the tape when the deck starts: the loading belt has broken or melted.[4]
  • The head loads and the deck stops almost at once: the computer has seen "tape end" because the take-up spool or the tape counter is not turning. Turn the take-up spool by hand; if the deck then keeps running, the sensor is working and the drive ring or counter belt is at fault.[4][10]
  • Fast forward and rewind do not wind the tape: the reel drive belt, or a gear held by hardened grease.[10]

Floppy faults (Model 20)

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The Model 20's internal drive is a TEAC FD-55BV-23, a 5¼-inch 2D drive that does not restore its head to track 0 at power-on; the computer does that when it first accesses the drive.[11] The drive cable is a separate part on the Model 20 and can be swapped to rule it out.[11]

A loud grinding at the first disk access usually means the drive cannot see track 0. The Sharp Museum traced this on an X1turbo drive to a failed track 0 photo-interrupter: the controller keeps stepping the head outwards because the sensor never reports track 0.[12] Check the sensor and its connector as described in Floppy Drive Repair.

The X1F's disk BASIC and most X1 software expect 2D disks. A disk written in 2D mode on a 2D/2DD/2HD drive, such as the CZ-520F or the drives in the X1turbo III and turboZ, may not read on a 2D-only drive.[13]

Power supply

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The supply is in a perforated metal box at the right rear of the case.[14] No circuit of it has been published; X1 Center found that even the full schematic of the first X1 leaves out the power supply.[15] X1 Center measured a healthy first-model X1 at about 22 W with the main power on and 26 to 27 W playing a tape, and notes that a failing supply loses efficiency and draws more. It tested a repaired supply from a current-limited 12 V source through a 60 W inverter, so that a remaining fault could not destroy the new parts.[15] Those wattages are for the first X1, not the X1F, but the method carries over: run the X1F through a plug-in wattmeter after any power supply work, and switch off if the reading climbs or the supply cuts out.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 X1 (コンピュータ), Japanese Wikipedia—link(accessed 2026-10-21) The IPL tries the FDD, an expansion ROM board and the CMT in that order and falls back to a menu of the three boot devices and the TV timer editor; the X1 has no system program in ROM and loads BASIC from tape, disk or a ROM board. The X1turbo and X1F added an IPL reset button beside the NMI reset; NMI reset jumps the Z80 to 0066h, and software not written for it can freeze. Separate keyboards use a 3-pole 3.5 mm plug; the 80C49 sub-CPU talks serially to the 80C48 in the keyboard, so the keyboard cannot report simultaneous key presses except Shift and similar keys.
  2. ↑ Oh!MZ, July 1985, pp. 26-27: the Model 10 is supplied with the tape BASIC CZ-8CB01 and the Model 20 with CZ-8CB01 and the disk BASIC CZ-8FB01. Scan on the Internet Archive, item oh-mz-1985, file Oh!MZ_1985-07.
  3. ↑ ゲームプレイ画面を録画可能！ X1シリーズで初めてビデオ出力端子を備えた「X1G」– 佐々木 潤 (Jun Sasaki), AKIBA PC Hotline! (Impress), 2019-01-29—link(accessed 2026-10-21) The X1G (1986) was the first X1 with a video output socket.
  4. ↑ 4.0 4.1 4.2 4.3 CZ-800Cカセットデッキの修理メモ, X1 Center—link(accessed 2026-10-21) On the first X1's deck: if the head does not load when playback starts, the loading belt has broken or melted into a sticky mass; if the head loads and the deck stops at once, the X1 has probably detected tape end because the cracked play-feed rubber ring leaves the take-up spool still; the sensor itself can also fail, but if the spool does not turn and the deck keeps running when you turn it by hand, the ring is the cause.
  5. ↑ 祝一平 (Iwai Ippei), 試験に出るX1 ハードウェアのフルコース (Nihon SoftBank, 1987), p. 78: the 80C49 in the main unit sits between the Z80 and the keyboard, cassette deck and µPD1990 clock; the 80C48 in the keyboard sends key data serially and one way to the 80C49; the X1F Model 20's sub-CPU differs from others because it talks serially to the 80C49 in the CZ-8RL1 data recorder. Scan on the Internet Archive, item SHARPX1TecRef.
  6. ↑ 6.0 6.1 6.2 佐藤 達之 (Sato Tatsuyuki), SHARP X1/X1Turbo キーボード端子 通信仕様 Ver 0.1, 2001, X1 Center, x1kbd.pdf, p. 1: one-wire serial from keyboard to main unit only, coded like an infrared remote control; 3.5 mm stereo mini jack with +5 V on the tip, the transmit signal on the ring and ground on the sleeve.
  7. ↑ X1シリーズで初となる5インチFDDを搭載した「X1F」– 佐々木 潤 (Jun Sasaki), AKIBA PC Hotline! (Impress), 2018-03-27—link(accessed 2026-10-21) Rear panel: power switch, RGB, TV control, printer, audio, joysticks, keyboard, with expansion slots above; a second keyboard jack on the left side of the front; the Model 10 has a high-speed electromagnetic-mechanism data recorder.
  8. ↑ キーボードコネクタの半田剥離, X1 Center—link(accessed 2026-10-21) Keyboard connector poor contact is a frequent fault on X1, turbo and Z machines; oxidation responds to contact cleaner; if keys work only with the plug pushed one way, the joints on the connector board are cracked and need reflowing.
  9. ↑ 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 coiled cord of X1 and X1turbo keyboards whitens and crumbles; the keyboard line carries +5.0 V, so shorts are dangerous; replace with a 3.5 mm audio cable.
  10. ↑ 10.0 10.1 10.2 CZ-8RL1カセットデッキの修理メモ, X1 Center—link(accessed 2026-10-21) The tape counter carries the tape end sensor, so a counter that does not turn makes play, fast forward and rewind stop almost at once; a seized fast-forward gear also stops play from working.
  11. ↑ 11.0 11.1 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-812C (X1F Model 20): TEAC FD-55BV-23, 5¼-inch 2D, step rate 6 ms, 1 kΩ input terminator, no restore at power-on; VFO MB84107; external connector pull-ups 150 Ω; the internal drive can be reached from the external connector and its cable can be replaced. The FDC in all models is thought to be an MB8877A.
  12. ↑ X1turboのよくある故障とその対処, シャープ博物館 (Nibbles Lab.)—link(accessed 2026-10-21) Faults met on X1turbo machines: a power-on failure caused by the digital telopper board loading the 12 V supply; RTC faults cured by adjusting the trimmer capacitor C4 on the 32.768 kHz crystal of the µPD1990; a grinding noise at boot from a failed track 0 photo-interrupter, which makes the controller keep stepping the head.
  13. ↑ 祝一平 (Iwai Ippei), 試験に出るX1 (Nihon SoftBank, 1987), p. 217: 2D disks written on three-mode drives (CZ-520F, X1turbo III and turboZ internal drives) are not guaranteed to read on 2D-only drives such as the X1G, X1turbo and X1turbo II internal drives and the CZ-800F, 801F and 502F; the author's test failed from track 35 on a turbo drive but read on a CZ-800F.
  14. ↑ Interior photograph, File:Sharp X1F Model 10 interior.jpg (AKIBA PC Hotline!), taken from above with the front of the machine at the bottom.
  15. ↑ 15.0 15.1 CZ800C電源修理・・・できなかった。, X1 Center—link(accessed 2026-10-21) Repair attempt on the first X1 (CZ-800C) power supply: the full X1 schematic has no power supply circuit; the unit carries many ZEBRA markings and appears to be a custom part; the inrush thyristor (2P2M) burst after one of the two 2SC2826 switching transistors (Q1, Q2) shorted; the 10 Ω 2 W start-up resistor also failed; the root cause was an open timing pulse transformer T2, which left Q2 running alone until it overheated; outputs 5 V standby, 5 V main and 13.8 V for the cassette; a healthy CZ-800C drew 0 to 1 W on standby, 22 W with main power on and 26 to 27 W playing a tape; a failing supply can lose efficiency and draw more; the repaired supply was tested from a current-limited 12 V source through a 60 W inverter and a socket wattmeter.


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