Hi,
Recently I've started to rebuild my collection of ZX Spectrums. And all of them have a faulty keyboard membrane.
I've bought from somewhere (if needed I can mention privately the source) and it seems that Spectrum+ membranes are faulty most of the time.
3 out of 6 membranes had problems with the combined keys (like arrows, delete, edit, etc). No matter what I have tried, those keys are not working.
The guy agreed to send me replacements, but it's annoying to buy a new part and just hope it's working.
The rubber key Spectrum membranes seem ok.
Can anyone let me know about source of reliable membranes?
Can the original membranes be repaired? I think most of them have problems with the ribbons. I have some conductive paint, used for car rear window defroster. Maybe that can help?
Zx Spectrum+ Membrane
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Ast A. Moore
- Rick Dangerous
- Posts: 2641
- Joined: Mon Nov 13, 2017 3:16 pm
Re: Zx Spectrum+ Membrane
Check out this post I made recently to respond to a similar concern.
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Re: Zx Spectrum+ Membrane
Hi,
I know that post. The trouble is that in this case, the keys are not working at all, not stuck keys.
I have a small bottle of conductive paint but no access to the traces, except from the area of the ribbons.
I know that post. The trouble is that in this case, the keys are not working at all, not stuck keys.
I have a small bottle of conductive paint but no access to the traces, except from the area of the ribbons.
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1024MAK
- Bugaboo
- Posts: 3118
- Joined: Wed Nov 15, 2017 2:52 pm
- Location: Sunny Somerset in the U.K. in Europe
Re: Zx Spectrum+ Membrane
Do you understand how the extra keys on the ZX Spectrum+ keyboard work (compared to the keys that are the same as the original ZX Spectrum)?
The operation of the extra keys on a ZX Spectrum+ keyboard very much depends on the ribbon cable clamps pressing the different membrane layers together so that they make electrical contact. The fixings have to be tight. But not too tight, or the threads in the holes will strip.
With old membranes, unless the damage is limited to the very end of the tails, it’s not worth the effort to try to fix them. As the plastic goes brittle. So the “repair” is unlikely to last long.
Also, most solvents will damage either the plastic, or the “glue” that holds the conductive layer on the plastic. So don’t use any solvent cleaner. If you use an abrasive cleaner, keep in mind that the conductive layer is VERY thin.
Mark
The operation of the extra keys on a ZX Spectrum+ keyboard very much depends on the ribbon cable clamps pressing the different membrane layers together so that they make electrical contact. The fixings have to be tight. But not too tight, or the threads in the holes will strip.
With old membranes, unless the damage is limited to the very end of the tails, it’s not worth the effort to try to fix them. As the plastic goes brittle. So the “repair” is unlikely to last long.
Also, most solvents will damage either the plastic, or the “glue” that holds the conductive layer on the plastic. So don’t use any solvent cleaner. If you use an abrasive cleaner, keep in mind that the conductive layer is VERY thin.
Mark
Standby alert “There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
Re: Zx Spectrum+ Membrane
Well, now I've studied a little bit the way it is working.
So, there are actually two keyboard membranes. The top one is almost identical with the rubber key model. The bottom one is managing the combined keys.
I have two faulty membranes.
One has Break, Delete, Edit and " faulty.
Luckily I have a bad membrane bought from the same guy one year ago. So I've peeled away all the layers to see how the tracks go.
In the first case, all keys are linked with the same trace as in the attached picture. None is working. So the fault must be somewhere around the red line.
There is no way it can be because of the clamps because the green track goes directly to the mainboard and the other layers that are connected to this one by the clamp work, so I assume that the interrupted part should be in the area of the red line. There is no visible damage.
I will check if I can find the exact spot, but I am not sure if I can do anything about this.
The other membrane has . and one of the arrows not working. By using the same technique I've found that the track used by these keys is also used by some other that are working, so the fault should be somewhere in the middle.
So, there are actually two keyboard membranes. The top one is almost identical with the rubber key model. The bottom one is managing the combined keys.
I have two faulty membranes.
One has Break, Delete, Edit and " faulty.
Luckily I have a bad membrane bought from the same guy one year ago. So I've peeled away all the layers to see how the tracks go.
In the first case, all keys are linked with the same trace as in the attached picture. None is working. So the fault must be somewhere around the red line.
There is no way it can be because of the clamps because the green track goes directly to the mainboard and the other layers that are connected to this one by the clamp work, so I assume that the interrupted part should be in the area of the red line. There is no visible damage.
I will check if I can find the exact spot, but I am not sure if I can do anything about this.
The other membrane has . and one of the arrows not working. By using the same technique I've found that the track used by these keys is also used by some other that are working, so the fault should be somewhere in the middle.
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1024MAK
- Bugaboo
- Posts: 3118
- Joined: Wed Nov 15, 2017 2:52 pm
- Location: Sunny Somerset in the U.K. in Europe
Re: Zx Spectrum+ Membrane
From your description, it does sound like a break in the conductor layer.
As you now know, the extra keys work by pressing four contacts together at the same time. This simulates the user pressing two keyboard keys at the same time on a rubber key keyboard.
On a plus keyboard, for the extra keys, one key operates one set (of 2 ‘contacts’) on one membrane pair and another set on the second membrane pair. Some membrane faults leave just one set of contacts working, depending on which bit has failed, depends on what the ZX Spectrum ROM code sees. So for example, if the caps shift key part is not working, the curser/ arrow keys will produce numbers (5, 6, 7 or 8). Whereas if the number part does not work, the key will appear to do nothing as there is no visible sign on screen when the caps shift key is pressed on its own...
Mark
As you now know, the extra keys work by pressing four contacts together at the same time. This simulates the user pressing two keyboard keys at the same time on a rubber key keyboard.
On a plus keyboard, for the extra keys, one key operates one set (of 2 ‘contacts’) on one membrane pair and another set on the second membrane pair. Some membrane faults leave just one set of contacts working, depending on which bit has failed, depends on what the ZX Spectrum ROM code sees. So for example, if the caps shift key part is not working, the curser/ arrow keys will produce numbers (5, 6, 7 or 8). Whereas if the number part does not work, the key will appear to do nothing as there is no visible sign on screen when the caps shift key is pressed on its own...
Mark
Standby alert “There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.