Question about HEF40106BP (74C14) Chip

Discussion in 'General Electronics Chat' started by duck11, Feb 11, 2009.

  1. duck11

    Thread Starter New Member

    Feb 11, 2009
    2
    0
    Hi, noob here. I'm not an electronics whiz but am not brain dead either.

    In looking the the PCB for the flasher relay rate for the turn signals is driven by an HEF40106BP chip, which from my research appears to be the same as the 75C14 chip.

    The circuit is designed to "hyperflash" if one of the bulbs goes out. I''d like to run LED bulbs in my motorcycle but apparently they don't have enough load and cause the lights to hyperflash. I've done some reserach and seen that other people have overcome this by cutting pins or traces to the chip. (Which aren't the same as mine but I'm guessing are similar.)

    Was hoping someone here might be willing to help me see if it's possible to modify the circuit so it won't hyeprflash if I run LED bulbs.

    Here's some pictures of both side of the PCB. I can provide more info as needed. Thanks.

    [​IMG]

    [​IMG]
     
  2. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    You have looked at the wrong component.

    Search and get a datasheet for U243B, which is a "warning and indicator" IC. A clip of the IC is shown below:

    The frequency doubling is in-built in the IC and depends on the voltage drop caused by lamp current across an external resistor. If you increase the value of this external series resistor to drop more voltage (~90mV or more) at the lower current requirement of the LED indicator, then the circuit will accept it as normal and not "hyperflash" your LED indicator.

    [​IMG]
     
  3. duck11

    Thread Starter New Member

    Feb 11, 2009
    2
    0
    Thanks. I'll chase the traces from that chip and see what I can figure out.

    What would happen if I found that resistor and cut the trace to it? That would give me infinite reistance.
     
  4. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    On the component board you will find a shinny "L" shape thin metal strip of width 8mm and length about 8cm mounted above the PCB and between the relays and U243B.

    In the image of your first post above it is that metal strip that has the reflection "TFK652" shown on it.

    This is the resistor R3 referred to in the datasheet.

    First you have to measure or determine how much total current the LED indicators are using, say X amps. This assumes you have two or more indicators in parallel.

    The R3 resistance is found by R3=0.1/X so if X=1 amp total then you should use 0.1Ω for R3. Similarly if X=0.5A then R3=0.2...etc. You can use 3W rating resistor for it.

    To have normal LED flashing you simply remove that metal strip and replace it with this new resistor. Doing so will retain the fault sensing function such that if one string of LED indicator fails, then the same "hyperflash" would be seen on the remaining good one.
     
    Last edited: Feb 12, 2009
Loading...