Sharp MZ-700 keyboard repair.

Back to the Sharp MZ-700. You may remember mine was missing a "blank" key. User psmart over on the Sharp MZ forum, very kindly provided me with a spare key and pillar/contact.

The machine is disassembled again...

(details here) 

The keyboard is flipped over. I want to avoid disconnecting that fragile keyboard connector, and making a load of work for myself. 27 screws are removed..

... and the PCB separated from the keys & frame.

As the key is missing, the keyboard is simply flipped over and the broken plunger falls out.

We need a spring, so time to rifle through the tub of junque fixings to see what we have that looks promising...

I'm kicking myself slightly here, as I junked a few old PC keyboards a couple of weeks ago that would have provided a perfect spring!

Hmmm ... 1 is too small and too stiff, 2 is too tall, 3 is way too stiff and 4 is suitable for closing a garden gate ...

Spring two is simply cut down to about 12mm long...

Looking good.

The replacement blank key snaps in place, and the tension is about perfect.

While the keyboard is in bits, the contact surfaces on the PCB are cleaned with a cloth and a bit of IPA. If your keyboard is not responding well, and needs a bit of force to work, you can clean the rubber contact surface on the plunger too. Mine works fine, so I'll not do that here.

The PCB can now be reassembled, taking care to ensure the power LED fits back through the hole.

And finally the machine is back together... 

A word on retrobrighting... Apparently these machines don't retrobright well, the legends fade on the keys. Now I've been watching a few YouTube videos on the chemistry and science behind retrobrighting. This one especially interests me https://www.youtube.com/watch?v=YPl356YKcVs&t=1557s 

What is interesting here is he uses a heat pad, rather than UV light, which is better for me, as I'm located in an overcast area of the UK. Sun is in short supply, and I don't fancy going out and getting a UV floodlight. Anyway, I won't be retrobrighting this unit, because of the tendency for the keys to fade.

What I did try was leaving it in the sun for a bit (when we were lucky enough to have some in early September (August was hopeless) .

Other than having to keep popping out, and bringing it in when it looks like rain. I think it's stating to make a difference... Look at the top and bottom section of the case here.. I'll carry on for as longs as the sun lasts!