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TI-99/4a keyboard woes


discgolfer72
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so I have 3 ti-99/4a computers siting here in front of me

one beige 2 silver

 

one of the silver ones works great but for some reason keyboard inputs are funky in basic

pressing f gives me a capital A

pressing r gives me space

pressing u is lowercase p

 

a lot of the keys work fine

machine launches cart games and plays them fine ( with a joystick)

 

any ideas where should I start

 

 

 

also since I'm here the white one just boots to a green screen with beep can use some input on it as well

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Look at the text on the initial two screens (before you input anything on the keyboard). Is the text sometimes garbled there too? If yes, it may be a bad video RAM chip. If the screens look good, it may be a problem with the keyboard itself (a broken or crossed wire).

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Your RAM is good. It looks like the problem is within the keyboard. Were you hitting each key multiple times or was it auto-repeating on you? Also, if you carefully pull one of the key caps off, is there a green box with two sets of metal fingers under it or is there a standard (more modern looking) stalk to plug the key cap into? At this point, it could be translation of the key matrix, bad connections, oxidation, or a broken keyboard wire.

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Your RAM is good. It looks like the problem is within the keyboard. Were you hitting each key multiple times or was it auto-repeating on you? Also, if you carefully pull one of the key caps off, is there a green box with two sets of metal fingers under it or is there a standard (more modern looking) stalk to plug the key cap into? At this point, it could be translation of the key matrix, bad connections, oxidation, or a broken keyboard wire.

i was pressing several times

looks like green stalk with copper contact inside

 

 

ps thanks

Edited by discgolfer72
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That is VERY good. You have one of the better keyboards. On keys that are sticking or not registering, you can clean the copper contacts (carefully). I'd look for a break in the 16-conductor flat cable that connects the keybaord to the motherboard next. . .those get stiff and brittle over time.

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That is VERY good. You have one of the better keyboards. On keys that are sticking or not registering, you can clean the copper contacts (carefully). I'd look for a break in the 16-conductor flat cable that connects the keybaord to the motherboard next. . .those get stiff and brittle over time.

to late tonight to tear her open

 

guess worst case i swap the motherboard from the silver one with bad kb to the white with bad mb

 

 

 

ok got some time swapped the keyboard from the white machine to the one with keyboard problems

the problem is still there

so its got to be in the motherboard itself

im tearing into the white motherboard trying to figure out why its borked right now

Edited by discgolfer72
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