It should be ~5V. Also, I should mention that when I say "base", I mean the base of the 2.5mm plug, so the contact at the bottom of the 2.5mm link port actually corresponds to the tip of the plug, and the contact at the side closest to the top of the mainboard corresponds to the base (ground). You still don't see ~5V with any combination of the three contacts?

Oops! I was measuring the wrong contact! It is right around ~5V, although it dips down every once in a while!


For reference, I have the multimeter set on 20 in the DCV category.

Okay, then a short in the I/O port or the lines connecting to the I/O port does indeed appear to be the culprit for your slow-flashing cursor and slow key detection. See if you can follow the traces that go to the link port and see if they've gotten shorted out somewhere.

Edit: Are both pairs 5V (base-tip and base-ring)? If only one is 5V, that will help you narrow down which trace to follow to look for a short.

Nope, both show the same reading. Is supposed to dip down every once in a while?


Edit: Actually, Base-tip is fine, however base-ring (the base and the two contacts on the side) are showing a low reading. One shows 0.02, and the other shows 0.00

Edit 2: I have tried multiple times to find a short in the traces, however have failed to find one. Maybe I'm missing something?

bump

edit: bump, again.

It's really hard to tell from that description, unfortunately. Remember, the tip is the contact at the "bottom" of the 2.5mm port, holding the mainboard rightside up. The two contacts on the side, from bottom to top, are ring and base. I'm unclear if tip-base and ring-base are each 5V or 0V.

Whoops, both show right around 5v, however, they fluctuate a little bit.

That is normal
Do you have another TI-83 Plus or TI-84 Plus calculator you can use to try communicating with it via the link port, or a SilverLink cable, just to make sure?

No, unfortunately I do not. I could get a hold of one, but not until september.

Edit: bump

In that case, I'm not sure what to suggest. Did you already try resetting the RAM and reloading the operating system? Other than that, and making sure that none of your keys are stuck, it still sounds like a problem with the link port (or with something else physical that was damaged near the crystal).

Yes, I've reset the RAM, and have reinstalled the OS. What if I desoldered the link port and reinstalled it. I doubt it would work, but should I give it a try?

Provided you trust your desoldering and soldering skills, it's unlikely that you could break terribly much by giving this a try. Unfortunately, since the original damage was closer to the ASIC and oscillator, I'd say it's also unlikely that it will help.

"It sounds like timer interrupt frequency is way down, if the keyboard response is poor. This might happen if it were mis-calibrated."

Since the link port seems fine, could this be the issue?


Edit: I'm not quite sure if this will help, however, the only thing I can not do on the calculator is turn it off. Every other key is responsive except for the On/Off key. The thing is, I can press the button and it will turn on perfectly fine.

Quick question: In the event that the calculator isn't fixed, is there any way to get a used TI-84+CSE replacement mainboard? I checked ebay, however most of the listings are just people trying to sell a gently used calculator for $80+.

Since its a newish product I havent seen anything of that sort on ebay (as most are under warranty still). The closest was a non working 84+CSE ... which wouldnt help you anyways :S.

Hmm... I've heard good things about the Nspire. Do you think it would be worth it to buy one of those?

It depends what you want to use it for. See our Back-to-School calculator guide for some thoughts on the strengths and weaknesses of the TI-Nspire line.