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blakespot

Very odd problem w/ keyboard, changes with heat perhaps...

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I have a '99 that I fitted with a F18a some months back. I've used it a good many hours without issue, and some of that was online through TIMXT with a WiFi232 -- so the keyboard has been working fine.

 

I'd not used the TI in a few weeks and turned it on and noticed in the FlashROM '99 menu that certain keys were not working. Those keys are:

 

HJKL; and SPACE

 

Press normal, hard, etc. and they don't register -- TI BASIC, TIMXT, Forth, etc. But, I left the machine on for a while and I notice they keys now do work...but you need to press them just a little harder than "normal" for them to trigger, and when you do, they usually repeat a few times. One depress of 'K' results in 'KKKK' and such. So something is really strange here.

 

I assume the hardware heating up is the change, but the repeat action baffles me. Can anyone make anything out of this? I see no other oddities with the system. I disconnected my PEB and that had no effect on the situation.

 

Is this a specific IC failing? Or...? Thanks.

 

 

 

bp

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First, do you know what kind of keyboard you have? Is it one of the Mitsumi or Alps types (as both of those can be very problematic)? If it one of the many other types (the ones with the square boxes under the keytops with metal fingers in them), I would try to carefully clean the fingers and verify that they still touch when the key is selected. Another possibility is that one of the keyboard lines is losing connectivity somewhere. . .

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HJKL; and SPACE

 

Those keys are all on pin 4 of the keyboard connector, so I'm with @Ksarul’s last suggestion. The repeats can be sticking keys or multiple making/breaking contact with the flaky connection going to pin 4.

 

...lee

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Don't worry, replacements shouldn't set you back more than $25 after Christmas time .

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I guess I may as well open it and reseat the kbd cable, etc. even though Ive not yet identified what ICs if any could alternatively be the problem.

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If reseating the cable doesn't solve the issue, you could reseat the 9901, as the keyboard connector ties back to that chip. Carefully check the ribbon connector at the keyboard side for a weak solder joint or break, especially if you removed it earlier to install the f18a.

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Yea... I pulled out the keyboard and took a look at the cable's solder connection to the keyboard's circuit board. Look close.

 

38971166831_5b1fa1c7a5_z.jpg

 

Full-sized original can be seen here.

 

Doesn't look so good, and the cable bends out from the plastic keyboard backplate so easily. Prob desolder that cable and either clip back that cable and expose some "fresh" wire or try and run individual wires from the board to the edge connector, having removed the original ribbon cable entirely. Or, other approaches? Thanks.

 

 

 

bp

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Yea... I pulled out the keyboard and took a look at the cable's solder connection to the keyboard's circuit board. Look close.

<snip>

Full-sized original can be seen here.

 

Doesn't look so good, and the cable bends out from the plastic keyboard backplate so easily. Prob desolder that cable and either clip back that cable and expose some "fresh" wire or try and run individual wires from the board to the edge connector, having removed the original ribbon cable entirely. Or, other approaches? Thanks.

 

 

 

bp

 

Well—the break on pin 4 confirms the problems with HKJL; and space. Several other pins are obviously compromised. You're on the right track, for sure!

 

...lee

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If you've got a piece of IDE cable kicking around, you can replace the original cable with that - just use every other conductor and the spacing is then about right, and cut the unused ones short.

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It's a definite weak point in the TI design. The same thing happened to me when I installed my PS/2 keyboard adapter and again when I installed an F18A on a secondary unit. After 37 years things are not always a flexible. In most cases I follow the, "If it's not broken, don't fix it" approach, but dang it... upgrades are so much fun. Good luck!

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Is there space enough to install a pin connector instead of soldering the cable directly to the board? That way the cable could be made replaceable?

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In revisiting this thread, I firmly believe that if 'someone out there' was able to conjure up a new keyboard connector assembly for us, many would be sold. Oh how nice would it be to have a new flexible cable with a working connector! I'm sure many of us would buy one, two, three or maybe more. Heck, I'll commit to two right now!

 

I think most people could solder on a new one. It's dealing with old fragile stuff that is so problematic.

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In revisiting this thread, I firmly believe that if 'someone out there' was able to conjure up a new keyboard connector assembly for us, many would be sold. Oh how nice would it be to have a new flexible cable with a working connector! I'm sure many of us would buy one, two, three or maybe more. Heck, I'll commit to two right now!

 

I think most people could solder on a new one. It's dealing with old fragile stuff that is so problematic.

 

I can make that happen I will look into it

 

Greg

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When looking for something else I spotted this ribbon cable at Micro Center and picked it up on impulse: http://www.microcenter.com/product/443175/200_mm_40_Pin_Plug_Leads_to_Plug_Leads_Ribbon_Cable

 

The square connectors it has are just the right size to fit on the pin connector on the TI's mainboard, just tear off a section with he 15 wires you need for the keyboard. Then I soldered a right angle inline pin header to the keyboard.

post-61132-0-00694000-1518011659_thumb.jpg

post-61132-0-04213000-1518011661_thumb.jpg

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a great idea, in fact I could put together a kit for this i'm sure. I'll do some looking for cheaper cables..

 

Greg

I get mine via AMAZON...

 

https://www.amazon.com/SINCODA-120pcs-Multicolored-Female-Breadboard/dp/B00ZWEFWO8/ref=sr_1_18_sspa?ie=UTF8&qid=1518022309&sr=8-18-spons&keywords=male+to+male+assorted+jumper+cables&psc=1

Edited by Sinphaltimus
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one thing to note - the connectors on these ribbon cables are a little bigger than the original ones. With the alps keyboard shown in my pics it fits in the case with the keyboard side sitting right on top of the mainboard side with maybe a 1/8-1/4 inch between them. If you have one of the keyboards without the metal bracket and the pcb that gets screwed right onto the posts you might need to use a flat pin header instead of the angled one I used here

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