Sharp X1 Troubleshooting Guide
These checks cover the first Sharp X1 (CZ-800C). No Sharp service manual for the X1 was found on the Internet Archive or X1 Center, so they are drawn from Sharp's owner's manual, the I/O magazine schematic that X1 Center offers for personal use, and repairs written up by X1 Center and the Sharp Museum. Opening the case, the strip-down order and the cassette belt sizes are on the Sharp X1 General Maintenance page.
What a working X1 does
[edit | edit source]- With the rear main switch on, press POWER on the front. If a CZ-800D display television is connected and its own main switch is on, it turns on with the computer and shows the computer picture.[1]
- The screen shows "Make ready any device" and "Push (F, R, C or T) Key". F, R and C boot from a floppy drive, a ROM board or the cassette, and T opens the clock and TV timer screen.[2]
- With the BASIC tape CZ-8CB01 in the deck, the deck clicks into play and the screen changes to "IPL is looking for a program from CMT". At about 005 on the tape counter it shows "IPL is loading BASIC CZ8CB01". At about 055 the deck clicks again, the play lamp goes out, the rewind lamp lights and BASIC starts.[2] Loading takes about two and a half minutes.[2]
First checks
[edit | edit source]- Rear main switch: it must be on before the front POWER switch does anything, and turning it off clears the TV timer settings.[3]
- Leave at least 10 seconds between switching off and on again, so that the microprocessors start reliably.[4]
- Cables: the RGB cable (8K-6D) for the picture, and the 8D-8D cable for television control when a CZ-800D is used. Sharp's own RGB monitors for the X1 were the 14M-112C and 12M-212C.[3]
- Keyboard: only one keyboard, in either the front or the rear jack, and nothing else in the other jack.[3]
- Options: if a fault appeared after fitting the graphics board or the expansion port, reseat their connectors (see opening the case).
Power faults
[edit | edit source]X1 Center rates the CZ-800C at 28 W, which matches Sharp's specification.[5][6] The Sharp Museum, which owns X1-family machines from the first model to the X1turbo Z III, has not had a power supply fail on any of them, so look for simpler causes first.[7]
Power use as a guide
[edit | edit source]X1 Center measured a healthy CZ-800C, and the same machine after its supply was repaired, through a plug-in wattmeter. X1 Center notes that a failing supply can lose efficiency and draw more power, so readings well above these are a warning.[5]
| Condition | Healthy machine (graphics board and floppy interface fitted) | Repaired machine |
|---|---|---|
| Standby (main switch on, POWER off) | 0 to 1 W | 0 W |
| Running, main board only | Not measured | 19 W |
| Running | 22 W | 22 W with graphics board |
| Cassette playing | 26 to 27 W | 27 to 28 W with graphics board |
| Floppy interface and FM sound card added | Not measured | 26 W; 32 to 33 W with cassette playing |
| Cassette fast forward or rewind | Not measured | 35 to 36 W, the highest load |
Supply failed with a bang
[edit | edit source]X1 Center's CZ-800C went silent with a noise like a gunshot and sparks from the supply. Working back through it showed a chain of failures that is worth knowing before you replace any single part:[5]
- One of the two pulse transformers (T2) that time the switching transistors had gone open on all four pins of its secondary winding. T2 and T3 are custom parts moulded into their plastic housings and cannot be repaired.
- With T2 open, switching transistor Q1 stopped and Q2 (both 2SC2826) carried the whole load. It overheated, melted the spacer holding its heatsink, and failed short from collector to emitter.
- The short across the +144 V primary supply sent a large current through the inrush thyristor, a 2P2M (200 V, 2 A), which split its case.
- The 10 Ω 2 W cement resistor in the start-up path then burnt open.
X1 Center's notes for anyone repairing this supply:[5]
- A blown thyristor is a symptom. The thyristor stays on once the machine is running, so it rarely fails by itself; look for a short or a drive fault before fitting a new one. X1 Center fitted a 2P4M (400 V, 2 A) because a 2P2M with a fin was not available.
- Check the primary reservoir capacitor for a short. X1 Center found it shorted, so its new thyristor would have blown again on mains power.
- Q1 and Q2 work as a pair. The 2SC2826 is no longer available; X1 Center replaced both with 2SC4105, so that the two halves match, and fitted silicone insulating pads.
- Test after repair from a current-limited source. X1 Center used a 12 V 5 A (60 W) DC supply feeding a 60 W car inverter, plugged into a wattmeter strip, so that the DC supply's overload cut-out protects the parts under test. The X1's start-up surge tripped that supply once before it restarted and ran normally.
The X1 schematics do not include the power supply, so X1 Center traced its circuit from the board, using the X68000 supply as a guide. Many of its parts are marked ZEBRA.[5]
Shuts down under load
[edit | edit source]After the repair above, X1 Center's machine ran normally until a 30-minute fast forward, then shut down when rewind started, with the supply too hot to touch. With the floppy and FM cards moved to the slots further from the supply it still shut down after 20 minutes. The 5 V sub supply was still alive; the 5 V main and cassette supplies rose part-way and collapsed. Only Q2's half of the supply had drive pulses, because T2 had failed. A supply that runs but collapses under load, especially during fast forward and rewind, should be checked for one switching transistor not being driven.[5]
Picture faults
[edit | edit source]- No picture: check the RGB cable, and on a CZ-800D check that the television is in computer mode. With the CZ-800D, switching the X1 off first returns the television to TV mode.[1]
- Graphics missing while text is normal: the graphics board (CZ-8GR) is an option on this model, and many games need it. If it is fitted, reseat it in its connector on the main board.[8][9]
- Text and attribute memory are two 2 KB static RAMs (IC7 and IC8 on the schematic), and the user-defined character memory is three more (IC5, IC6, IC11). If characters or their colours are corrupt across the whole screen, start with these chips and the bus buffers beside them on sheet 3 of the schematic.[10]
Cassette faults
[edit | edit source]The built-in data recorder is electromagnetically controlled by the sub-CPU. Its rubber parts perish with age, and X1 Center finds that renewing them cures most deck faults.[11][12]
| Symptom | Likely cause | Remedy |
|---|---|---|
| On play the head does not move into the loading position | Loading belt melted or broken | Remove the residue and fit a new flat belt.[12] |
| The head loads, then the deck stops at once | The play and fast forward ring has cracked, the take-up sprocket does not turn, and the X1 probably reads this as the end of the tape. Check by turning the sprocket by hand: if the deck keeps running, the ring is the cause. | Fit a new ring; it can be reached from the front.[12] |
| Reels do not wind on play, fast forward or rewind | Square drive belt stretched or deformed | Fit a new belt.[12] |
| Tape runs but programs will not load or save | Dirty record and playback head | Clean the head; Sharp asks for this monthly.[4] |
Belt and ring sizes are in General Maintenance.
Keyboard faults
[edit | edit source]- Keys work only while the plug is pressed in one direction, or not at all: the keyboard connector's solder joints inside the computer have probably cracked. X1 Center lists this among the commonest faults on the X1, turbo and Z series. Try the other keyboard jack, then reflow the connector's joints.[13]
- Cord sheath cracked or falling apart: replace the cord, because it carries +5 V.[14]
- Two keys pressed together, other than SHIFT and similar keys, are not both detected. The X1 keyboard sends key codes serially and cannot report a full key matrix, so this is normal.[11]
Clock and timer faults
[edit | edit source]- Clock wrong when first set up: Sharp notes that the clock display may not be correct and that this is not a fault; set it again through the T option on the IPL screen.[1]
- Clock loses time with the power off: the backup is a 2.4 V nickel-cadmium cell (BA1), which Sharp rates at about two weeks of running with the main switch off when fully charged. An old cell may no longer hold a charge, and a leaking one damages the board around it; see clock backup battery.[3][10][15]
- Clock does not run at all: the µPD1990AC clock chip uses a 32.768 kHz crystal with a trimmer capacitor (C1) on one side.[10] On the X1turbo, the Sharp Museum traced stopped clocks to the matching trimmer, whose contact had aged so that the crystal no longer started. Turning it slightly with a fine screwdriver to a fresh part of its track brought the clock back; check by watching the clock on the timer screen.[7]
Related pages
[edit | edit source]- Sharp X1
- Sharp X1 General Maintenance
- Sharp X1 Capacitor Replacement Guide
- Sharp X1F Troubleshooting Guide and Sharp X1D Troubleshooting Guide, for later X1 models
References
[edit | edit source]- ↑ 1.0 1.1 1.2 CZ-800C 取扱説明書, File:Sharp X1 CZ-800C Owner's Manual (Japanese).pdf, page 26 of the scan: with the CZ-800D's main power on, switching the CZ-800C on turns the CZ-800D on in computer mode, and switching the CZ-800C off first returns the CZ-800D to television mode; the clock and timer are set from the IPL screen with the T key, or with ASK from BASIC; the clock display may not be correct, which is not a fault, and should be set again by the clock setting procedure.
- ↑ 2.0 2.1 2.2 CZ-800C 取扱説明書, File:Sharp X1 CZ-800C Owner's Manual (Japanese).pdf, pages 17 and 18 of the scan: "Make ready any device", "Push (F, R, C or T) Key" with F floppy, R ROM, C CMT, T timer; with the BASIC tape CZ8CB01 loaded the deck clicks, the play lamp lights and the screen shows "IPL is looking for a program from CMT"; near 005 on the counter "IPL is loading BASIC CZ8CB01"; near 055 the deck clicks again, the play lamp goes out, the rewind lamp lights and the screen shows that BASIC has loaded; loading BASIC from cassette takes about two and a half minutes.
- ↑ 3.0 3.1 3.2 3.3 CZ-800C 取扱説明書, File:Sharp X1 CZ-800C Owner's Manual (Japanese).pdf, pages 12 to 15 of the scan: RGB cable 8K-6D and TV control cable 8D-8D to the CZ-800D, or the RGB cable alone to the 14M-112C or 12M-212C; the rear main switch cuts the power completely and clears the timer settings; the clock runs from the internal battery for about two weeks with the main switch off when the battery is fully charged; never connect two keyboards or anything other than the keyboard to the keyboard jacks.
- ↑ 4.0 4.1 CZ-800C 取扱説明書, File:Sharp X1 CZ-800C Owner's Manual (Japanese).pdf, page 11 of the scan: leave at least 10 seconds between turning the power off and on so that the microcomputers start reliably; do not plug or unplug with the switch on; clean the cassette record and playback head once a month, because a dirty head prevents correct saving and loading.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 CZ800C電源修理・・・できなかった。, X1 Center—link(accessed 2026-10-21) A CZ-800C supply failed with a gunshot-like noise and sparks; the thyristor's housing had split; the thyristor limits inrush current and stays on after power-up, so it seldom fails by itself; no supply schematic in the X1 schematics; many parts marked ZEBRA; traced with reference to the X68000 supply; a failing supply can lose efficiency and draw more power, so a wattmeter is useful; test rig of a 12 V 5 A 60 W supply, a 60 W car inverter and a wattmeter tap, since the DC adapter cuts out on overload; rated 28 W; healthy machine with graphics RAM and FD interface: standby 0 to 1 W, main power on 22 W, cassette play 26 to 27 W; inrush trips the test supply once, then it recovers; thyristor 2P2M 200 V 2 A replaced by 2P4M 400 V 2 A; 10 Ω 2 W cement resistor open, replaced with two 5.6 Ω 2 W in series; primary capacitor shorted; switching transistor Q2 shorted C-E and its heatsink spacer melted; 2SC2826 unobtainable, Q1 and Q2 (push-pull pair) both replaced with 2SC4105, insulators replaced with silicone; after repair 5 V sub, 5 V main and 13.8 V cassette supplies correct; standby 0 W, main board 19 W, cassette 23 to 24 W, with graphics RAM 22 W and 27 to 28 W playing, with FD interface and FM board 26 W and 32 to 33 W playing, fast forward and rewind 35 to 36 W; ageing test: shut down after 30 minutes of fast forward when rewind started, supply too hot to touch; cards moved to slots 2 and 3, further from the supply; shut down again after 20 minutes; primary charge and 5 V sub alive, 5 V main and 13.8 V rose part-way and shut down; Q2 side had switching pulses, Q1 side none; T2 timing pulse transformer open on all four pins of its secondary (the supply's primary side); T2 and T3 are custom parts moulded into their plastic housings; failure sequence: T2 open, Q1 stopped, Q2 overloaded and shorted C-E, +144 V primary shorted, thyristor 2P2M burst, 10 Ω resistor burnt open.
- ↑ Sharp Corporation, パソコンテレビX1 パーソナルコンピュータ CZ-800C 取扱説明書 (owner's manual, Japanese), File:Sharp X1 CZ-800C Owner's Manual (Japanese).pdf, page 66 of the scan: power consumption 28 W (keyboard and computer), 50 W with options connected.
- ↑ 7.0 7.1 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) Of about six machines from the mania-type X1 to the X1turbo Z III, none has had a power supply fail. Clock not running (cursor not blinking, TIME$ errors): the µPD1990 RTC's 32.768 kHz crystal has a trimmer capacitor (C4) to ground on the X1turbo; ageing of the trimmer stops oscillation, and turning it slightly with a fine screwdriver restores it; check on the BIOS timer screen; the same circuit is used up to the X1turbo Z III.
- ↑ CZ-800C 取扱説明書, File:Sharp X1 CZ-800C Owner's Manual (Japanese).pdf, pages 63 and 64 of the scan: the CZ-8GR graphics V-RAM plugs its connector A into connector B on the main board.
- ↑ ～ シャープ X1 ～ （レトロな○○ギャラリー）– 後藤 儀兵衛 (Goto Gihei), AKIBA PC Hotline! (Impress Watch), 2013-02-26—link(accessed 2026-10-21) The optional graphics video memory board is essential for games; Vegetable Crash is one of the few games that do without it.
- ↑ 10.0 10.1 10.2 CZ-800C(X1) Rev.4 全回路図 (I/O誌), X1 Center—link(accessed 2026-10-21) Sheet 2: µPD1990AC (IC9), 32.768 kHz crystal X1 with trimmer C1 (20 pF) and C2 (22 pF); backup cell BA1 2.4 V. Sheet 3: text RAM IC7 (CHA) and attribute RAM IC8 (ATT), 2 KB static RAMs (5128), with LS541 and LS373 buffers between them and the data bus. Sheet 4: PCG RAMs IC5, IC6 and IC11 (5128) and character generator ROM IC4.
- ↑ 11.0 11.1 X1 (コンピュータ), Japanese Wikipedia—link(accessed 2026-10-21) The data recorder's deck is electromagnetically controlled and can be operated by programs; the 80C49 sub-CPU communicates with the 80C48 in the keyboard and controls the data recorder; because of the serial keyboard link the key matrix cannot be read and simultaneous key presses, apart from SHIFT and similar keys, cannot be detected.
- ↑ 12.0 12.1 12.2 12.3 CZ-800Cカセットデッキの修理メモ, X1 Center—link(accessed 2026-10-21) Cassette decks deteriorate with age and changing the rubber belts usually cures them. Loading belt failure: the head does not load on play. Play feed ring failure: the head loads then stops, probably because the X1 detects tape end; if the feed sprocket does not turn and the deck does not stop when the sprocket is turned by hand, the ring is worn; it can be reached from the front. FF/REW square belt deformed: the reels do not wind on play, fast forward or rewind.
- ↑ キーボードコネクタの半田剥離, X1 Center—link(accessed 2026-10-21) Poor contact or a dead keyboard connector is a common fault on the X1, turbo and Z series; if the keys work only with the plug pulled one way, the connector's solder has cracked; reflow the joints on the connector board; most models have two keyboard jacks.
- ↑ 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 keyboard curly cord sheath crumbles with age; +5.0 V is present on the keyboard line, so a short is dangerous.
- ↑ 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 with age or over-discharge and corrodes the board around it.