+2a problem

Lost · January 2014

Hi guys just got a +2a from eBay. I can get the menu screen but none of the keys work.

I had a look at the membrane, and it looks faultless.

Anyone had a problem like this? Could it be more serious than a membrane issue?

Any help would be appreciated.

balford · January 2014

Yep, I had the same problem with an otherwise pristine +3 I bought last year.

I disassembled the keyboard and gave the membrane surface a good wipe down with a clean dry cloth, reassembled and reinstalled, and it's worked without problems from then on.

Worth a try anyhow?

B

Lost · January 2014

Will try this now.

Lost · January 2014

Wiped the membrane, tbh looked OK though, just a bit of light dust.

Pressed reset with the break key pressed and get the test screen. So that key is working.

Lost · January 2014

Pretty sure its the membrane. I removed the keyboard and made a few connections using a bit of wire and that worked fine. The weird thing is I can't see any issue with the membrane. It looks fine!

balford · January 2014

Amstrad membranes in my experience are pretty robust, but that's not to say that they don't ever fail, of course :)

If point to point connections at the keyboard sockets produce key presses that the keyboard itself can't produce, then the membrane is the obvious culprit.

Would be handy though if you had another +2A/+3 keyboard assembly available to double check....

B

Pierre · January 2014

balford wrote: »

Yep, I had the same problem with an otherwise pristine +3 I bought last year.

I disassembled the keyboard and gave the membrane surface a good wipe down with a clean dry cloth, reassembled and reinstalled, and it's worked without problems from then on.

Worth a try anyhow?

B

I had exactly the same with my +2a. It worked perfectly after re-assemble

Pierre

Lost · February 2014

balford wrote: »

Amstrad membranes in my experience are pretty robust, but that's not to say that they don't ever fail, of course :)

If point to point connections at the keyboard sockets produce key presses that the keyboard itself can't produce, then the membrane is the obvious culprit.

Would be handy though if you had another +2A/+3 keyboard assembly available to double check....

B

Just got my hands on another keyboard assembly. Should sort the issue.

Are these membranes hard to come by Now? Google hasn't turned much up.

balford · February 2014

Found some +2A/+3 ones here, not sure if that site's current though. Grey +2 ones seem to be unobtanium alright.

B

Lost · February 2014

Frustration overload!!!

The membrane is working. I hooked up some jumpers and did a continuity test. When I pressed the key I'd hooked up, guess what? It worked.

Then I connected the other end of the jumpers to the molex input on the mother board, and now I have a working enter key.

Cleaned the molex with a bit of paper, re connected everything and it doesent work. :confused:

Everything is working, just not together!!!

1024MAK · February 2014

Is the membrane making good contact in the molex connector?
It should be a tight-ish fit.

Mark

guesser · February 2014

1024MAK wrote: »

Is the membrane making good contact in the molex connector?
It should be a tight-ish fit.

If not, try cutting a piece of card the same as the bit stuck on the keyboard tail and stuffing that in at the same time. If even that won't help get a tight fit in the socket it suggests the connectors in the socket aren't springy any more :(

Lost · February 2014

The contacts look good. The bottom connection seems to be working, the issue it the top lot.

The odd thing is when I just use a bit of wire to make the connection it works OK. This is with the bottom ribbon connected to the motherboard, and a wire connecting pin one on the top molex with the ribbon, and while the enter key is depressed.

When I plug the ribbon into the top molex the I can no longer make a connection even if I use the wire to make the connection.

When I take the ribbon back out the wire can make the connection again.

BruceNorton · February 2014

I've just had the same problem on a +2a. Machine looked almost new. However after resetting the machine 5 times it started working perfectly.

Lost · February 2014

It is the membrane that is at fault. The second connection on the top ribbon some how causes a short that stops the others working.

I have disabled this connection and the rest works fine. Need a new membrane then, dam.

One day I'll buy a speccy with a working keyboard!

1024MAK · February 2014

Here is what my +2B looks like (note most +2A's are actually +2B's):-

+2B keyboard ribbon photo 1

+2B keyboard ribbon photo 2

Mark

Lost · February 2014

Thanks mark, mine looks exactly the same.

I now have all keys working except for the keys That work off line 2 of the top ribbon.

I have cut the membrane in a way that allows me to exclude that set of keys. However, doing this change allows all other keys to work.

When I re connect line 2 the only key that works is break.

Hope this makes sense, i'll try to post pics later this week.

Surely the fault is with the membrane, as it acts as a number of "push to make" switches. So if it was working correctly there would be no issue from just inserting the ribbons. If the membrane was working and the motherboard was at fault then the issues would only start when you pressed a key to make the connection.

I'm assuming that when no key is being pressed the membrane is invisible to the motherboard.

1024MAK · February 2014

Lost wrote: »

I'm assuming that when no key is being pressed the membrane is invisible to the motherboard.

Yes, and I suspect that somewhere you have the membrane equivalent of a stuck down key connected to line 2 of the top ribbon....

If you disconnect both ribbons, it may be possible to work it out using a meter on resistance (ohms). In a normal situation, the electrical contacts (conductive traces on the inside of the different layers of the membrane) should not touch unless you press it (or a key presses it). The conductive traces of the ribbon make up a matrix. So there should be no electrical contact between any ribbon line and any other.

Of course, it may be quicker to have a really good look using a good light.

I think someone published a diagram of a +2A/+2B/+3 matrix, but I forget where (sorry).

Mark

Lost · February 2014

1024MAK wrote: »

I think someone published a diagram of a +2A/+2B/+3 matrix, but I forget where (sorry).

Mark

I did look for this, but couldn't find it. I have been mapping it out the old fashioned way. My eyes are no good for this task, however, I can now narrow it down to the handful of keys not working, which helps.

There is some damage to the case of this machine, suggesting its been dropped in the past. It was also thick with dust and bits of crap, so I guess its been in the loft for some time. There is some corrosion on the tape head, which I'll clean when I fit the new drive belt. Apart from that, its in "excellent condition" :-D

Lost · February 2014

All is good. I got my new keyboard and membrane today, and a new drive belt, so I've completed the refurbishment and even loaded a few games.

The seller has also refunded some cash due to the problems, and that has covered all my additional costs.

And I will still try to fix the old keyboard when I get time, as its an option for the Harlequin keyboard.

:grin:

balford · February 2014

Lost wrote: »

And I will still try to fix the old keyboard when I get time, as its an option for the Harlequin keyboard.
:grin:

You're out of luck there, as all machines except the +2A/+3 have 5 x 8 molex connectors for the membrane, as will the Harlequin :)

B

Lost · February 2014

May mount switches under the keys and go without membrane.

Also, would it be possible to connect this to new style molex, and do some kind of translation?

Where there's a will...:-D

+2a problem

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