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Power Issue?

Discussion in 'Power Electronics' started by partyanimallighting, Aug 28, 2019.

  1. partyanimallighting

    partyanimallighting

    278
    2
    Oct 22, 2012
    Hi Wizards, I'm having a little issue with a dimming console and I haven't been able to pinpoint the problem. I used this unit last weekend and it worked fine but I tried powering it up afterwards and there was no display and all the LED's were flashing constantly. I disassembled the unit and, assuming the problem was on the voltage side, checked the adapter voltage and the voltage out of the regulator and everything seems to be fine, 9VDC and 5VDC respectively. I switched it off (disassembled) and when I checked it a couple days afterwards, it started up perfectly, but when I switched it off and back on, the problem returned. The voltage readings out of the regulator are 4.7VDC so that's fine but the LED's are still flashing and there's no display, no function. I left the unit off for a while and it started up without issues but I switched it off and back on and the flashing returned. I downloaded the datasheet for the SN74HC02 and took some readings and I've posted them in the pix as this chip seems to send voltages out of 4 different gates and the 4390 Op Amp doesn't seem to be getting proper voltage. I also checked the capacitors next to the LM7805 and their readings are correct. Any feedback would be great! 2019-08-28 10.13.10.jpg 2019-08-28 13.10.02.jpg 2019-08-28 13.09.46 REV. II.jpg
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,192
    2,694
    Jan 21, 2010
    4.7v from a 5v regulator is not good.

    Is it hot? If so there is most likely some sort of overload.

    Is the voltage stable, and the regulator cool? It may be a fault regulator.

    Does the voltage vary, from a max of 5v down to something a lot lower? (You may need an oscilloscope to check this). Could be a regulator fault or some sort of repetitive high load condition.

    Is it's an easily replaced and cheap regulator, I'd just swap it out as that eliminated the regulator as the problem.
     
  3. partyanimallighting

    partyanimallighting

    278
    2
    Oct 22, 2012
    Hey (*steve*), the problem was not the regulator or the console. The bleeping power supply. I didn't checking about checking it because the unit started up fine on more than one occasion and I was getting DC voltage on the regulator. The power supply is rated at 9VDC 1.0A and when I checked it, it was only outputting around 6VDC. I changed it out with one outputting 9VDC @1.65A and everything's fine now. I just don't know why I didn't take a closer look at it as I normally check from AC source first then into DC. Sorry for the post, which could have been avoided if I was more meticulous. :(:(:(
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,192
    2,694
    Jan 21, 2010
    Yeah, and I totally ignored possible problems with the unregulated DC rail. I'm glad you found it.
     
  5. partyanimallighting

    partyanimallighting

    278
    2
    Oct 22, 2012
    Thanks again. The original response was really fast! :):):)
     
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