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Help with LM3914 please, LED stuck on.

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Externet

Well-Known Member
Hi.
LED on pin 11 is on, circuit works properly otherwise.
Replaced the IC twice, same behavior.
Picture shows circuit, green LED on pin 14 is on as supposed to, plus the problem red one on pin 11.
(the input voltage comes from a frequency-to-voltage converter LM2917N-8, which also works fine. LEDs indicate frequency inputted, for 30, 40, 50, 60, 70, 80... Hz
P1010504.JPG
 
Sounds like an incorrect or shorted connection. Does it light with power applied and no chip?
 
Thanks.
With no chip and power applied, no light.
With chip with pin 11 lifted out of the socket, no light. :banghead:
 
Pin 7 and pin 8 make an adjustable voltage reference. Why aren't you using it to make the 5.2V reference?

With a 5.2V reference voltage, each LED at the outputs of the LM3914 turns on with 520mV more than the previous one so the 1st LED is 520mV, the 2nd is 1.04V, the 3rd is 1.56V, the 4th is 2.08V, the 5th is 2.6V and the green 6th LED is 3.12V.
The datasheet shows high leakage current from pin 1 (not pin 11) that needs a resistor parallel to the LED to shut it off. It shows 20k parallel with the LED on pin 11, try it, but the resistor might need to be as low as 2.7k.
 
Thank you.
Those are very close to the voltages delivered by the LM2017 into pin 5 of the LM3914. I used the internal 7.6V regulator of the LM2017 (dropped to 5.2V) to feed pin 6 of the LM3914 with 5.2V because the power supply for the circuit comes from variable AC.

Solved !
A finer than a hair solder splash thread from pin 8 (GND) to open pin 9 (DOT). Took two loupes for tired eyes.
Tested on bench and then on my portable generator that I replaced the exploded governor mechanism inside the crankcase. Set the speed to 60 Hz successfully.
 
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