Replacing a Sinclair QL Keyboard Membrane

The Sinclair Quantum Leap or QL. I'd been looking forward to getting one for some time. It's a classic model for all the wrong reasons, but I wanted one anyway.

Figure 1. Sinclair QL

Two weeks ago one arrived from Australia via eBay. On first inspection it seemed fine. The computer booted, and the microdrives seemed to work with most wafers. Until I tried out Psion's Quill that is. It was then I discovered that about 1/4 of the keys didn't work! Bugger. "As is" is "as is" so I couldn't take it back to the seller. Besides that, the seller was a long way away. I doubt if he was even aware of the fault.

Time to see just how common and/or serious this problem was. Google revealed that non-working keys in vintage QL were not so much as problem as a standard fitting! Invariably, the membrane becomes brittle over time and keys simply start to fail.

I'd dealt with a membrane keyboard before on my Atari 800Xl, so I opened up the case for a look. The membrane LOOKED alright, but grasping the membrane between forefinger and thumb and simulating a key press did reveal many of the connections were dead. Reseating the ribbon in its connector on the motherboard made no difference.

Figure 2 - Sinclair QL - Naked, showing detached keyboard membrane!

I wondered if it might be a blown keyboard controller chip, as all the offending keys seem to be on the upper right hand side? In other words there seem to be a pattern which may conform to bitmapping. However, I found if I half closed the unit and tried keys, some keys stopped working that actually did work when the keyboard ribbon was stretched out rather than bent. I decided that it was indeed the keyboard membrane and went about looking for a new one.

All hail to the Internet! It is truly a global shop. In no time at all I found a firm that was selling replacement keyboard membranes for 19 GBP. I ordered one of these and two weeks later it was here. I fitted it today. A very simple job that took about 15 mins. That was indeed the problem as all keys now work and the QL is now fully functional.

Figure 3. Sinclair QL. All good.

Hopefully this new keyboard will last quite a few years. It says it's made of "improved material" so we shall see.


19th October, 2008

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