Problem with testing WB (heater circuit)

[Brian Renegar]

Thanks for the suggestions guys.  I will try to do some more testing 
tonight, and let you know the result.

Thanks,
Brian


>I would suggest you use the 10 ohm, 5 ohm resistor test
>for the heater ckt I previously described.  With a 10 ohm
>in place of the sensor heater (at terminals J1, J2) the
>LED should come on.  If it does, you should see about
>10.4 V across the resistor.  It will heat really fast unless
>you have a 10 watt resistor.
>
>Correct voltages but no LED could be reversed LED.
>Vout will never vary from 2.5V until the LED is on.  If
>the voltage from the junction of R7-Q1to gnd rises to
>near battery V but no LED, check voltage across LED.
>More than 2V means its bad or reversed.
>
>If that works, put the sensor heater back and monitor the
>voltage across it.  It should rise to 10.4 V in 1/2 minute
>and the LED come on.  During this same time, voltage
>across R4 should be 1.25 V, decreasing slightly as the
>LED comes on.  If J1-J2 voltage is way low, look for a
>short (C3 backwards?).   If you are close to correct, its
>possible your sensor needs a bit more than 1.5 A, which
>the WB can't deliver.  Get back with test results, we could
>do a work around to save an extreme sensor.
>
>Bruce Roe

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