Yashica YC-64

The Yashica YC-64 was an MSX 8-bit microcomputer manufactured by Kyocera.

Symptom or Problem Encountered
The mains transformer hums loudly.

Causes

 * Unknown

Solutions

 * Unknown

Disassembly Notes
Getting the case open requires the unscrewing of two screws on the bottom, towards the back.

Then there are three tabs where the red upper cover needs to be pried outward from the bottom part of the case: One tab in the middle of the back, and one tab in the middle of each of the sides.

Once these are loose, the back side of the red cover can be gently lifted up a few centimeters, and pulled towards the user or more precisely towards the front of the machine.

Note that the tab on the back, and the tabs on either side, are shallow, probably one millimeter or less. You should be able to pry them out with a flathead screwdriver without worrying too much about breaking anything.

The three tabs on the front are significantly longer, and the plastic is brittle. It is not necessary to use force on these, as they slide right out after you have loosened the three other tabs. If you do use force on them, they will probably snap right off.

After the cover has been lifted off, the two-pin connector for the power LED can be pulled from its socket on the main board before you can put the cover aside.

The keyboard has two flat-flex connectors that go to sockets on the motherboard. First unlock the sockets, then gently pull out the flat-flex. After that, the keyboard can be lifted right off.

Keyboard
Warning: Do not use a key puller to remove the keys from the keyboard. There are plastic hooks on each key that sticks through the mounting plate, and if you pull on the keys you risk damaging these hooks.

Most of the keys have two springs under each key. There is one wide spring that makes the key bounce back after you release it. The spacebar is the only exception; it has two of the wide springs.

Then there is a thinner spring that sits in the middle of the wide one. The thin spring is the actuator that makes a keypress register when you depress a key.

It might be possible to remove most keycaps by pulling them straight out, but it’s not recommended. Each keycap has two plastic tabs that holds the cap down to the board, and if the plastic has become brittle, they might snap.

Also, the only way to remove the left shift, space, and enter key without damaging them, is to unscrew the back plate first. These keys are rather long, and they are attached to metal stabilizer bars that ensure that the keys depress evenly.

On the Yashica, these stabilizer bars are rugged, and they need to be removed before pulling the keycaps. Failing to do so will damage the keycap.

Unscrew all the little screws that held the back plate in place, and everything will come apart nicely. Slide the three stabilizer bars for the left shift, space and enter keys sideways, and pull them out.

Now get the thin springs out and put them in a container.

Use a small screwdriver or other pointy object to carefully push the keycaps out of the black plastic frame. If you have long or pointy nails, you might even do without any tools for this job.

Original Parts
The main board has no revision number or model identifier on the silkscreen. The PSU board has the code. The graphics daughterboard has the code  and.

Main Board
board)

Sub Board (attached to main board)
If parts are not available or different selection is preferred, you can use the values in the Original Parts section to perform a parametric search.

Kits

 * Digikey BOM: https://www.digikey.com/

Related Links

 * A blog post about the YC-64
 * The MSX wiki page about the YC-64
 * The oldcomputers.com page about the YC-64
 * A very barren page about the YC-64