Yamaha D1500 Audio Level Meter with Dead LEDs

Discussion in 'General Electronics Chat' started by lahatte, Sep 22, 2017.

  1. lahatte

    Thread Starter New Member

    Jul 26, 2017
    5
    0
    I wonder if someone can describe how the LED meter in the attached works? It's a strange arrangement, difficult for me to understand.

    My issue is that I have some LEDs in the meter that do not light. I actually made it worse by trying to apply some voltage to some to see if they would work or if it was the driver at fault. So there's that. Now only the top three LEDs in the stack will light up.

    I got a new IR2E19 chip, and saddled it over the existing one to see if it would make any difference. It did not.

    Any ideas?

    Thanks.

    Yamaha_SPX90_mono_LED_Meter_IR2E19.jpg
    Attached Thumbnails
     
  2. MrChips

    Moderator

    Oct 2, 2009
    14,514
    4,279
    I am sorry to inform you that you are making some terrible mistakes.

    1) You cannot test an LED with "some voltage". You are likely to destroyed the LED as well as IC301.

    2) You cannot stack another chip on top of IC301 and expect the circuit to work.

    That's two strikes against you.
     
  3. lahatte

    Thread Starter New Member

    Jul 26, 2017
    5
    0
    Thanks very much. I was uncertain about the stacking bit. Without access to a data sheet for that IC I don't know how it works. I just thought I would try it.

    As for the "some voltage", I used what I found at the IC. But yes, you are right, certainly.

    Based on the diagram I posted above it looks like the LEDs have a hot leg constantly attached to power, and the LED driver provides the LEDs with a path to ground through the various pins 1 through 7. So what I have done to try and test the LEDs is to set my multimeter to read Ohms to act as a resistor to make the ground connection for the LEDs. I didn't know if that would work, but it does somewhat. I then put one lead on pin 8 of the driver IC (ground) and touch the other lead to the pins 1 through 7 as a convenient way to access the LED meter stack. Labeling the 7 LED's in the meter stack from top to bottom as 1 through 7, connecting the free multimeter lead to pin 1 makes the top three LEDs (1, 2, and 3) light, to pin 2 LEDs 2 and 3 light, and to pin 3 LED 3 lights. On pin 4 I get no LED lighting, and nothing will make any of the LEDs below 3 light up.

    This makes me think that the LEDs 4 through 7 are not working, since I am giving them a path to ground.

    Agree? Disagree?

    Thanks.
     
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