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Cory

What's this mod do?

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Does anyone know the purpose of this mod?  It appears to be tied to the keyboard, but not clear what the diode is protecting.  

 

Also, should I be posting these types of topics in this thread or the development thread?  

IMG_3075.jpg

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1 hour ago, Cory said:

Also, should I be posting these types of topics in this thread or the development thread?  

This would not be a development topic.

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Looks like the motherboard equivalent of the diode fix for the capslock/joystick up fix..

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14 minutes ago, OLD CS1 said:

This would not be a development topic.

Thank you.  I'll post future topics like this over there.  

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9 minutes ago, jedimatt42 said:

Looks like the motherboard equivalent of the diode fix for the capslock/joystick up fix..

Thank you!  

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This is the perfect place to ask this type of question. Lots of interesting discussions about what was possible have resulted from past questions like this.

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Given the tip from @jedimatt42, I found a previous post on the topic:

 

And read the article on http://www.mainbyte.com/ti99/console/alpha_lock.html

 

Does placing the diode on the motherboard save you from modifying the keyboard like this instructions from the mainbyte site: 

... you must remove a part of the lead that originaly ran to from the alpha-switch and the connector 6 on the keyboard connector

 

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I'm still astonished TI didn't include this from the beginning. I could understand if they had removed the diode in the later reductions of all costs, when they tried to save millicents, but from the beginning?

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This is a non-obvious glitch that you don't see in the schematics. So the design was done, and it seemed too late to change it. In the QI they actually fixed it.

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Posted (edited)

Curious whether the diode placement on the motherboard saves you from cutting the trace on the keyboard between the alpha lock and pin 6 on the keyboard connector.  It seems to me that it would and would be a simpler modification.

 

Is that true?

 

I guess "simpler" is a bit of a subjective term since you have to desolder a component to squeeze the diode in.

Edited by Cory

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