Sharp MZ-80K (1978)

Sharp MZ-80K

The first personal computer produced by Sharp. I thank my friend Carlo who lets me raid his warehouse where he hides some very significant items.

On the 100th anniversary of its foundation in 1912, Sharp published an interesting pdf that describes the most innovative products and the history of the Company.

In May 1978, the Components Division of the Electronic Components Group introduced the MZ-40K microcomputer kit, and in December, the MZ-80K, an assemble-it-yourself model that ran under BASIC. This was Sharp’s first personal computer.

The statement “ran under BASIC” is a bit a bit misleading though: on boot, the computer doesn’t include any programming language except a simple monitor with a few commands, such as for loading a program from tape (LOAD) or from disk (FD).

So to use BASIC, the most common language in the home computers of the time, you need to load it from disk or tape. Fortunately I got the expansion module and dual floppy drive together with the main unit, with the original Disk BASIC and its manual. Furthermore, always useful, I found the service manuals for all the three items.

Sharp MZ-80K - Disk BASIC

The computer, based on the Z80 processor, was only dirty and didn’t have any problems. The power supply unit doesn’t have a filter capacitor (that usually blows up in a cloud of stinking oily smoke), so I just took it apart to clean it as usual. Here’s the long image that shows all the main parts of the computer:

Sharp MZ-80K - exploded view

This is the motherboard:

Sharp MZ-80K - motherboard

A detail of the monitor after removing 30 years of dust:

Sharp MZ-80K - CRT

The tape reader mechanics:

Sharp MZ-80K - tape reader

And the power supply unit:

Sharp MZ-80K - power supply

Here are some pictures after reassembling the Sharp MZ-80K:

Sharp MZ-80K - right

Sharp MZ-80K - back

Sharp MZ-80K - left

Usually you have to unscrew 4 screws to get to the inside of the computer, that can be “clamshell” opened; but most of the times – and this time is no exception – they are missing.

Sharp MZ-80K - open

Sharp Interface Unit MZ-80I/O

Sharp MZ-80I/O - front

This element is basically an external expansion box, where you can add up to 5 cards. The only card I have is the dual floppy drive controller.

Sharp MZ-80I/O - top

The only intervention was the replacement of the power supply filters, the usual Rifa that crack, dry, and burst after two minutes of usage, tainting all nearby components and filling the room with smoke. Despite my experience I turned on the box, and the filter exploded earlier than usual. At least I was prepared and in less than 10 seconds I unplugged, sealed the room and opened the window :-)

Sharp MZ-80I/O - filters

With two shots on a tripod, I created an image showing in transparency the inside of the box. The side door can be opened by unscrewing a couple of screws.

Sharp MZ-80I/O

Sharp Floppy Disk MZ-80FD

Sharp MZ-80FD - front

This is the double 5¼-inch floppy unit. As I turned it on I saw a flash of light and heard a popping sound: the fuse just blowed up. I was testing all the items with a friend who, unlike me, is really good at electronics; he searched for a short circuit after the fuse, and his suspects proved right: we unsoldered a few capacitors until we found the shorted one, a small 10µF 35v tantalum capacitor.

Sharp MZ-80FD - top

The following morning I went to a local shop and bought some fuses and 5 capacitors. I replaced the shorted one and the fuse, I checked for short circuits, then I turned the unit on. A flash of light, another fuse blown: a second capacitor went off. I replaced all 5 tantalum capacitors, then a couple of power supply filters.

Sharp MZ-80FD - capacitors

This is the drive logic board:

Sharp MZ-80FD - drive pcb

Two pictures of the drives:

Sharp MZ-80FD - drive

Sharp MZ-80FD - drive

A detail of the stepping motor:

Sharp MZ-80FD - stepping motor

So finally everything was cleaned and repaired and I could hook the drive to the interface unit and then to the computer, load BASIC and write some lines of code. It’s a bit hard to get used to the keyboard. Here it is:

Sharp MZ-80K - keyboard

A final picture of the whole system where you can see the BASIC just booted from floppy.

Sharp MZ-80K

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