Stop the keyboard ribbon from cracking

Discussions about Sinclair ZX80 and ZX81 Hardware
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nama
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Joined: Fri May 09, 2008 3:49 pm

Stop the keyboard ribbon from cracking

Post by nama » Sat Sep 16, 2017 9:41 am

My present ZX81's keyboard ribbon cable is actually in pretty good shape, but I've had machines in the past with the dreaded cracked ribbon syndrome. I was wondering if some pre-emptive maintenance, in the form of sellotape (maybe the wide packing tape variety), would be beneficial.
By this I mean taping a strip of tape on both the top and bottom of the ribbon (both ribbons I guess), right around where it goes through the tight bend. could this help make the ribbon last longer and stop the cracking in the future.

(Hope this makes sense, it's a bit hard to explain.)

What does everyone think?

Phil

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1024MAK
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Re: Stop the keyboard ribbon from cracking

Post by 1024MAK » Sat Sep 16, 2017 10:07 am

That's something that I don't have an answer for.

It's thought that heat speeds up the chemical changes that occur within the plastic used to make the membrane. Expansion and contraction caused by the heating/cooling cycle will not help either. So one way to increase the life of the membrane, is to reduce the amount of heat in the case.

The greatest sources of heat are (in order):
  1. The 7805 series pass type voltage regulator - because a transistor inside it is used as a series pass element, it "drops" the voltage of the input to the required 5V. The difference is lost as heat. Remove the existing 7805 and fit a modern switching DC/DC converter like a RECOM or a TRACO type. More details in the note below.
  2. The ULA produces a fair amount of heat. But until another modern plug in module is produced, there is not a lot that can be done here.
  3. The Z80 CPU only runs slightly warm, so apparently not much of a gain in heat reduction. But fitting a modern CMOS type will reduce the current consumption from the 5V rail, and hence will also reduce the amount of heat given out from the 7805. Every little helps (he said pinching the tag line from an advert...).
  4. Although the RAM and ROM chips don't produce much heat, it's also possible to replace them with modern CMOS chips. The modern CMOS chips are much lower power devices.
Notes:
The subject of using a switching regulator in place of the 7805 series voltage regulator has come up a number of times before.
Either use a RECOM or a TRACO type. Part numbers in this post.
Have a look at this recent thread where there is some discussion and pictures ;)
And ‪Pictures of my ZX81 fitted with a RECOM 5V Regulator

Mark

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PokeMon
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Re: Stop the keyboard ribbon from cracking

Post by PokeMon » Sat Sep 16, 2017 4:07 pm

Yes indeed. The "plasticizer" get lost over the years (vaporizes) and due to heat, make the membrane harder and brittle.

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gammaray
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Re: Stop the keyboard ribbon from cracking

Post by gammaray » Wed Sep 20, 2017 12:44 am

Different approaches have been used from a new reproduction of keyboard to more flexible cable. I have found a new replacement can still be subject to the stress of assembly andwith original molex orientation. I would at least make the simple mod even with new keyboard/ribbon.
KEYBOARD.jpg
KEYBOARD.jpg (64.93 KiB) Viewed 153 times
Finish what you start. Truth is over the mountaintop or six feet under.
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