Sharp X1 General Maintenance

An X1 with its top cover off, seen from above with the front at the top. The optional graphics board stands upright on the main board, under the metal bar that stiffens the case (photo: Goto Gihei, AKIBA PC Hotline!, copyright Impress Watch)

Routine care of the first Sharp X1 (CZ-800C) centres on the cassette deck, the keyboard cable and the clock battery, and most jobs start with opening the case. Sharp's own instructions below come from the CZ-800C owner's manual. The strip-down order and belt sizes come from X1 Center, which has repaired these machines. No Sharp service manual for the X1 was found on the Internet Archive or X1 Center.

Safety

The X1 has a mains switching power supply inside the case. With the cover off, the supply's primary side and its large reservoir capacitor are exposed; on the CZ-800C supply that capacitor charges to about 144 V DC. Sharp's manual says not to switch the computer on with the cover removed, because circuit parts can be damaged and there is a risk of electric shock, and not to leave screws or other metal parts inside the case.

• Switch off at the rear main switch and unplug the mains lead before taking any screw out.
• Before touching the power supply board, measure across its reservoir capacitor and wait until it has discharged.
• If you must run the machine open for a measurement, keep hands and probes away from the supply.

Everyday care

Sharp's handling notes for the X1 are:

• Keep the ventilation slots clear. Do not push the computer into a tight space, cover it with cloth or stand it on carpet or bedding.
• Keep it away from damp and dust, direct sunlight and heaters.
• If liquid or anything metallic gets inside, unplug it at once and have it checked.
• Do not drop it or knock it.
• Unplug it if it will not be used for a long time.
• Clean the case with a soft cloth dampened with water or a little detergent. Benzine, thinners and other solvents discolour the cabinet.
• In an electrically noisy place, use a mains line filter, and keep the RGB and TV control cables away from mains leads and other equipment.
• Leave at least 10 seconds between switching off and switching on again, so that the microprocessors start reliably. Do not plug in or unplug the mains lead with the power switch on.
• A static picture left on the display television for a long time can burn into the screen.

Power switches

The main power switch on the back cuts the supply completely, and turning it off clears any TV timer settings. The POWER switch on the front is the one for everyday use: it latches on when pressed and releases when pressed again, and the timer keeps running while it is off. With the main switch off, the clock runs from its internal battery for about two weeks if the battery is fully charged.

Keyboard jacks

The keyboard can plug into the jack on the front or the one on the back. Never connect two keyboards at once, and never plug anything other than the keyboard into either jack. The keyboard line carries +5 V.

Cassette head

Sharp asks for the record and playback head of the built-in data recorder to be cleaned once a month, because a dirty head stops programs saving and loading correctly. A cleaning cassette from a shop is the simplest way.

Opening the case

1. Switch off at the rear main switch and unplug the mains lead.
2. Take out the four screws that hold the top cover and the two screws on the underside.
3. Lift the top cover off.

Inside, a metal bar runs across the top of the chassis to carry the weight of a display television. The graphics board, when fitted, stands upright in the middle of the main board, and the power supply is in a perforated metal box at one side.

Fitting the CZ-8GR graphics board

The CZ-8GR graphics V-RAM comes as a board on a mounting bracket.

1. Fix the bracket carrying the graphics board to the angle inside the computer (angle A) with the two screws supplied.
2. Plug the board's connector (connector A) into the main board's connector (connector B).
3. To remove the board, reverse the steps.

Fitting the CZ-8EP expansion I/O port

The CZ-8EP is a frame with four slots that fits inside the computer.

1. Remove the reinforcing angle from the top of the computer.
2. Fix that angle to the top of the expansion I/O port with the two screws supplied with the port.
3. Lower the port into the computer from above, the way round shown in the manual, and push its connector into the square connector on the main board.
4. Fix the angle and port back to the computer with the two screws removed in step 1.

Fitting interface cards

With the CZ-8EP fitted, interface cards go in through the panel at the back.

1. Remove the two screws holding the connector panel and take the panel off.
2. Remove the two screws holding the blanking cover to the panel.
3. Slide the card in along the port's rail guides, component side up, and push it fully into the slot connector.
4. Refit the panel, fix the card to it with the cover screws, and screw the panel back in place. A card without a rear connector does not need the cover removed.
5. Fix cable connectors to the card with their screws so that they cannot pull out.

Taking the computer down to the cassette deck

To change the loading belt, X1 Center found that the CZ-800C has to be stripped almost completely, main board included. Its order is:

Strip-down order (X1 Center)

Step	Remove	Notes
1	Cassette door cover	Slide it upwards to release it.
2	Top cover and rear panel	Screws only.
3	Graphics board, expansion I/O port and the upper stay
4	Main board	There is a plastic screw near the RGB output. Take care not to break it.
5	Power supply	Remove the two screws in the side, then slide the supply forwards. This is only needed if the front panel is coming off.
6	Frame and front panel	Six self-tapping screws. X1 Center thinks the deck may come out without removing the front panel.
7	Cassette deck	Four self-tapping screws, one of them shorter than the others. X1 Center thinks the belts may be reachable without taking the deck out.

With the deck out, the screw to the right of the motor gives access to the belts. Reassemble in the reverse order, and check that no screws or offcuts are left in the case.

Cassette deck belts

Rubber parts in the X1's deck perish with age. The loading belt is the worst: it is made of a butyl-like rubber that melts into a sticky mass and glues itself to the pulleys and anything else it touches. Remove it before anything else, scraping it off with a flat screwdriver or spatula and cleaning the residue with parts cleaner on a rag. It stains clothing permanently, so wear overalls.

X1 Center measured the original parts and tried these replacements:

CZ-800C deck rubber parts (X1 Center)

Part	Original, as measured	How it fails and what you see	Replacements X1 Center tried
Loading belt (flat)	111 mm lay-flat length (70 mm diameter) when already stretched and broken; 0.5 mm thick; 4.0 mm wide	Melts and turns to goo. On play, the head does not move to the loading position.	Sengoku Densho flat belt, 60 mm diameter × 0.5 mm × 5 mm, which X1 Center found slightly tight; a belt the size of the stretched original (70 mm diameter) is far too loose. As a stopgap, a Cemedine XA-590 rubber band (80 mm lay-flat, 11 mm wide) cut to half width; it is natural rubber and will not last.
Fast forward and rewind belt (square)	68 mm lay-flat length (43 mm diameter) × 1.2 mm square, on a working deck	Deforms if the deck is left unused for a long time. The reels do not wind on play, fast forward or rewind.	Not replaced by X1 Center. Suggested, untested: Sengoku square belt 40 mm diameter × 1.2 mm or 45 mm diameter × 0.95 mm. A rubber band will do as a stopgap.
Play and fast forward rubber ring	10.5 mm inside diameter, 16 mm outside diameter, 2.5 mm thick	Cracks and splits. The head loads, then the deck stops at once: the take-up sprocket does not turn, so the X1 sees a tape end. If the deck keeps running when you turn the sprocket by hand, this ring is the cause.	INAX LF80 piston packing, part INPA5005. It is slightly thick and has to be pushed into the groove, but works well. The ring from the CZ-8RL1 data recorder does not fit.
Tape counter belt (square)	86 mm lay-flat length (54 mm diameter) × 0.9 mm square, on a working deck	Deforms if the deck is left unused for a long time.	Not replaced by X1 Center. Suggested: Sengoku square belt 45 mm or 50 mm diameter × 0.95 mm (untested); Nisshinbo Mobilon band, medium (80 mm lay-flat × 0.3 mm × 3 mm), which worked on an X1C.

The play and fast forward ring can be reached from the front without stripping the whole machine. After fitting new rubber, run a tape through play, fast forward and rewind before trusting a program to the deck.

Keyboard

Keyboard cable

The curly cord on X1 and X1turbo keyboards ages badly: its outer sheath goes white, cracks and falls away in pieces. Replace a cracked cord, because it carries +5 V and a short can do damage. X1 Center's method:

1. Remove the six screws on the underside of the keyboard and take the case apart.
2. Unplug the cable's three-pin connector from the keyboard board.
3. Pull out the pin that holds the cord bush in the metal plate, and take the cable out.
4. The bush cannot be replaced, but its material ages better than the cord. Ream the old cord out of it carefully with a drill so that the bush can be used again.
5. Fit a new cable with a 3.5 mm three-pole (stereo) mini plug. An audio cable or earphone lead works electrically; a curly cable of the original diameter has not been found. Thread it through the bush and fit the three-pin connector taken from the old cable.

Keyboard connector in the computer

A keyboard that works only while its plug is pressed in one direction, or not at all, usually has cracked solder joints on the keyboard connector's board inside the computer. X1 Center lists this among the commonest X1 faults and a weakness Sharp never fixed, from the first X1 to the turbo Z series. Contact cleaner can fix a dirty or slightly oxidised contact. For cracked joints, take the computer down to the connector board and reflow the joints.

Clock backup battery

The calendar clock is kept running by a 2.4 V nickel-cadmium cell (BA1 on the schematic), which is charged through a diode and a 3.3 kΩ resistor (D1 and R8). These cells leak with age or after deep discharge. The electrolyte first roughens the solder resist, then soaks through the plated holes and eats the copper until tracks break. On X1 Center's CZ-800C board the plated holes near the transistor beside the cell had turned black, and reheating them brought brown liquid bubbling out.

• Look at the cell and the board around it whenever the case is open.
• If you do not need the clock to keep time with the power off, X1 Center suggests removing the cell or fitting a supercapacitor rated at 5.5 V in its place.
• After removing a leaking cell, clean the electrolyte off the board and check every track and plated hole near it for continuity. On a later X1 board, X1 Center spent about 15 minutes re-tinning the blackened plated holes around the cell and found one track under it broken.

After any work

1. Check that no screws, washers or wire offcuts are left inside.
2. Refit the top cover before switching on.
3. Switch on at the rear main switch, then press POWER. The IPL menu, "Make ready any device", should appear on screen.
4. Load a program from cassette to check the deck, and press every key, including the television and cassette control keys.

Maintenance checklist

Task	When
Clean the cassette head	Monthly in use (Sharp)
Check the clock battery for leakage	Whenever the case is open
Inspect the keyboard cord for cracking	Whenever the keyboard is handled
Check the deck belts and ring	When the deck misbehaves, or before using a machine that has been stored

Related pages

• Sharp X1
• Sharp X1 Troubleshooting Guide
• Sharp X1 Capacitor Replacement Guide
• Sharp X1F General Maintenance and Sharp X1D General Maintenance, for later X1 models