Texas Instruments TI-89 Tip List page 154

Troubleshooting
If the BCC cable does not work, first verify that:
1. You are using the latest version of the TI GraphLink software.
2. You have selected the Black Cable option in the GraphLink software.
3. You have selected the correct serial port for your computer.
4. You have reasonably fresh batteries in the calculator.
5. Both the GraphLink and serial port connections are secure. On the TI-89, in particular, the
GraphLink cable connector must be firmly pushed into the calculator connector.
If all this seems correct, check the BCC circuit itself. Most circuit flaws are caused by mis-wiring. In
particular:
1. Verify that the diode polarities are correct.
2. Verify that the transistor connections (base, emitter and collector) are correct.
3. Verify that the plug, tip and base connections are correct.
4. Verify that the serial port connections (RTS, CTS, TX, DSR and DTR) are correct, for the
connector you are using - either the 9- or 25-pin.
5. Verify that all component connections are correct. Use a voltmeter with a continuity function
(beeper). For example, verify that RTS is connected to D1, R1 and Q3's emitter. Verify that the
plug base connects to D2, D3, R2, R3, R5, R6 and TX, and so on.
6. Verify that the correct resistor values are in the right places.
7. Check the schematic and verify that you have, in fact, built the circuit shown.
Some circuit flaws are caused by soldering problems:
1. Carefully check the circuit for shorts (unintentional solder bridges between pads or leads).
2. Check all solder connections for cold joints. A good solder joint has a shiny, smooth
appearance. A cold joint has a dull, rough appearance. A cold joint may be mechanically solid
but may not be a functional electrical connection.
If all this fails to get the BCC working, have someone else check your work. This is helpful even if
(particularly if!) the person has no electronics experience. Sometimes, just explaining the circuit to
someone else will make a mistake obvious.
It is remotely possible, but unlikely, that failed parts cause the BCC fault. Transistors and diodes can
be damaged or destroyed outright by the heat from excessive soldering times. Again, the most likely
cause of failure is mis-wiring.
Comments
The serial port input lines (CTS and DSR) have a relatively low impedance of about 5Kohm. The are
not high-impedance inputs.
If either of the data lines (plug or ring) are asserted low, calculator operation may become sluggish
because the calculator thinks that communications is in progress. It appears that the GraphLink
software does not set the DTR and RTS lines high on all computers when the software is started. This
may prevent the calculator from being put into 'receive' mode, and it may also prevent sending
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