[1.13] Developer's Guide Describes Calculator Internal Operation; [1.14] Cleaning A Calculator After Spills And Other Accidents - Texas Instruments TI-89 Tip List

My test results do not support this theory. However, during my testing I did notice that, at very low
battery voltages, the calculator will turn itself off while the program is running. This effect may cause
the GraphLink transfer failures. Another possible cause is that low battery voltages reduce the voltage
levels of the GraphLink signals such that they no longer meet the minimum requirements for successful
transmission.

[1.13] Developer's guide describes calculator internal operation

The SDK developer's guide, formally called the TI-89 / TI-92+ Developer Guide, is a 1400-page
document which describes much of the internal operation of the calculator. While this document is
intended to enable software developers to write calculator applications, it is interesting reading even if
you have no intention of writing applications, but you are just curious as to how your calculator works.
While registration is required to download the complete SDK, you may download just the guide, without
registration, at
http://education.ti.com/developer/8992/down/download.html

[1.14] Cleaning a calculator after spills and other accidents

Accidents happen even if you are careful with your calculator. If you spill a drink or liquid into your
calculator, such as milk, carbonated beverage or juice, it should be cleaned out, otherwise damage will
probably result. Short-term failures include complete failure, sticky or inoperative keys, or intermittent
display operation. Even if no immediate failure is evident, the spilled liquid can cause long-term failures
through corrosion.
If your calculator is under warrantee or you are not confident in your ability to disassemble your
calculator, consider sending it to TI for repair or replacement. Most users have reported that TI is fairly
cooperative in working with them.
There is some risk in the cleaning procedure, but if your calculator has failed completely, you have
nothing to lose, anyway.
The key principles for a successful cleaning job are to clean the calculator as soon as possible after
the spill, clean it thoroughly, and dry it completely and quickly. The purpose of the cleaning process is
to remove the contaminants from the calculator components with damaging the calculator. All batteries
must be removed before attempting a cleaning.
Clean water is probably the best fluid to use to clean a calculator. Other solvents such as alcohol may
damage the calculator. While it may seem strange to wash electronics with water, this is common in
the electronics industry. At my firm, we have been washing printed circuit boards after assembly, in a
dishwasher, for over fifteen years. We have fairly stringent reliability requirements, and the washing
process improves reliability by removing the solder flux before conformal coating.
This process has been successful in cleaning a variety of spills:
1. If the calculator seems to be working, back up the calculator memory with GraphLink.
2. Disassemble the calculator. See instructions below.
3. Gently scrub the printed circuit board (PCB) with warm water and a clean toothbrush. Rinse
frequently. Use distilled water, or softened water, because hard water will leave calcium
deposits. Alternatively, you can secure the parts to be washed in a dishwasher, and run the
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