Trying to resolve issue with electronic gadget

Discussion in 'The Projects Forum' started by rnbguy, Jun 6, 2011.

  1. rnbguy

    Thread Starter Member

    Oct 8, 2008
    10
    0
    Hi Guys,
    I've got this circuit I'm trying to test U1 which is an IC driver. I'm trying to identify if the driver is dead by measuring the voltage on pin 1OUT, I'm getting no voltage and no amps from that pin. Every other pin both in and out are reading ~11.5volts. Can someone point me in the right direction of how this works.
    [​IMG]
    Please know I'm new to this
     
  2. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    The edges of your schematic are not visible. You should verify 24V from J3 to U1 pin 1. I assume there's at least 14V since the 11.5V output is present on U1 pin 8.

    Here's a datasheet for U1 http://focus.ti.com/lit/ds/symlink/tps2813.pdf. Here's one for the optoisolator U2 since it's a likely failure point http://www.fairchildsemi.com/ds/4N/4N36-M.pdf.

    The 11.5V from the regulator output U1 pin 8 will be present on several pins of U1 including 1IN U1 pin 2 since it's pulled up to VCC by R12. When the transistor in U2 turns on it will sink 1IN to ground.
     
    Last edited: Jun 13, 2011
  3. rnbguy

    Thread Starter Member

    Oct 8, 2008
    10
    0
    interesting reply... I can see 24V@J3 pin 1, what makes you say u2 is the issue? if u1 is getting the right voltage everywhere? is it because 1IN isnt sinking into the ground?
     
  4. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
    363
    I didn't say U2 is the issue. I said it's a likely failure point. Optoisolators fail on the emitter side when overloaded with excess input current. The regulator portion of U1 is functioning but you need to determine if 1IN or 1OUT ever change state. This would be a good place for an oscilloscope.

    Is there any chance that the rest of the schematic will appear?
     
  5. rnbguy

    Thread Starter Member

    Oct 8, 2008
    10
    0
    thanks, i'll add the rest of the diagram once i get back from work, i have a 1mhz oscilloscope, will that be fine, i'm not sure how to tell the frequency i need
     
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