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Chemistry Electronics Services
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Bad jacks in Texas Instruments calculators (TI-83, etc.) with Vernier LabPro

TYPICAL FAILURE:

Fairly old Texas Instruments graphing calculators give a communication error when linked together to transfer programs, or when used in classrooms with Vernier LabPro. This happens because the internal jack in the TI-83 wears out over time (especially it wears out with heavy student use.)

The tiny gold leaf-springs get crushed out of the way so they no longer make contact with the jack. Sometimes you can open the calculator case and use a needle to bend them back again, but this is a temp fix and doesn't always work. And in an education lab environment, they will immediately go bad again.


For those skilled with soldering, the 2.5mm connector is not that difficult to replace in on your own. However, only a somewhat-similar part is available. I've never found a source for the original gold-plated surface-mount 2.5mm stereo sub-miniature jack. Digi-key sells a useable replacement, their number CP-2523SJCT-ND, but one terminal-pad is in the wrong place, and the tiny alignment posts on the bottom will not match the holes in the calculator circuit board.


Digi-key part: http://www.digikey.com/product-detail/en/SJ-2523-SMT/CP-2523SJCT-ND


WARNING: TEXAS INSTRUMENTS WANTS YOU TO SHIP THESE BACK TO THE FACTORY FOR FREE REPAIR!!! If you want to tear into these yourself, you take responsibility for possibly messing up the electronics.

NOTICE: OPENING THE CASE WILL DISCONNECT THE MEMORY BACKUP BATTERY AND WIPE OUT ANY PROGRAMS YOU'VE STORED.

To get inside many TI calculators, the screws require a #6 spline screwdriver such as Xcelite 99-62. Fortunately a 1.5mm hex (allen) screwdriver works great, and probably you can even use a 0.050" hex wrench if you tilt it so the points grip the inside of the screw. (And, the older TI calculators just use normal phillips-head screws.)


Before soldering in the new jack, slice the *rear* tiny pin off the bottom, the tiny black bump which is furthest from the jack entry hole. The front pin still provides some alignment, so leave that one as is. You might wish to affix the jack to the board with a bit of cyanoacrylate glue before soldering. (The jack will be under large forces during use, so a drop of crazy-glue will prevent this failure from coming back so soon.) The rear terminal on the new jack does not match the PCB pad, and it also touches against the PCB ground. I bend these rear terminals upwards out of contact with the PCB, then solder a short piece of bare wire between the PCB's pad and the bent terminal. A bit of resistor-lead works fine for this. Note: when reassembling the calculator, make sure all the calculator keys line up with the keypad holes in the case before replacing all the screws.


Note that these calculators will "forget" their LCD brightness setting. Don't panic if the display seems blank when you reassemble the unit. Hit the ON switch, and look for the phrase "Mem Cleared" on the display. Then type [2ND][UPARROW][2ND][UPARROW] over and over to find the correct LCD brightness setting.


Vernier LabPro, bad jack


The same Digi-Key part CP-2523SJCT-ND can be used to repair bad TI calculator jacks in Vernier LabPro units, but the larger height of the new jack makes the fit even more of a problem. If you really want to repair your own LabPro using the Digi-key part, you'll have to take a chance and do some slight case-modifications where the blue plastic walls in the rectangular well are pushing against the top of the new jack. And as above, slice off the tiny rear alignment pin on the bottom of the jack, use a tiny bit of crazy-glue to bond the jack to the PCB, and solder some bare wire to connect the rear terminal pad to the PCB pad.


See also:
Created and maintained by Bill Beaty.



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