LED VU METER  (277-0116)         Troubleshooting       Faxback Doc. # 15158

If difficulty is encountered, the first thing is to recheck your
construction:

a)  Use assembly diagrams to check that all resistors are installed with
    the proper value.  In particular, 10K resistors (Brown, Black, Orange)
    and 100K resistors (Brown, Black, Yellow) are easily mistaken, as are
    other resistors which differ only in the third color band.

b)  Make sure that the electrolytic capacitor C4 is installed with the
    negative and positive terminals connected as shown on the instructions
    and on the Board itself.

c)  Check that both diodes CR1 and CR2 are installed with the banded end
    toward the edge of the board.

d)  Check to be sure that pin 1 of the integrated circuits is mounted in
    the pin 1 location and that no pin has been folded under the IC rather
    than through the board.

e)  The LED's should be installed with the negative (cathode) terminal to
    one of the 470 ohm resistors R1-R8.  (This can be checked by applying
    3V or more to the "+" terminal and grounding the terminals of R1-R8
    opposite the LED's; this should light the corresponding LED.  If the
    LED does not light, it should be reversed or replaced.  Do not apply
    a voltage directly across the LED.)

f)  Make sure that all components are soldered properly, and that the
    board has not been shorted with solder bridges between I.C. pins or
    other closely spaced connections.

g)  The signal input and ground must not be reversed.  Also, check to make
    sure that the supply voltage and ground are not reversed. and that the
    signal and supply voltage are not reversed.

h)  If the trimmer potentiometer (R38) is grossly misadjusted, either all
    or none of the LED's will light up.  Recalibrate as noted earlier.

j)  If all the LED's light up when there is any input signal and trimmer
    potentiometer (R38) is adjusted full counterclockwise (as viewed from
    the input end of the printed circuit board), the sensitivity of the
    unit is too high for the voltage used.  Connect the input signal to
    IN1 and re-calibrate.  (Make sure R39 is 1 Meg  - Brown, Black,
    Green.)


(lb/all-05/08/95)