No Power to OSSC V1.5

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  • November 23, 2017 at 12:35 AM #17440
    renegadeandy
    Participant

      Hi All.

      I have completed my soldering of the OSSC V1.5, and am experiencing an issue where there is no obvious signs of life in the device.

      My power supply is providing a steady 5V, and is capable of delivering up to 2 amps if required.

      I tested each of the 8 regulators on the board, and they are all behaving as expected – delivering their appropriate voltages, and only the middle pin being grounded.

      Neither of the 2 fuses are blown, however strangely if I test the voltage at F2, I see 0.3V, when I would expect to see 5V!

      Is there anything else I should be checking, what could be the cause of this?

      I also started trying to debug U7 and U4 and couldn’t get my head around their behaviour.

      U7 had 0.6V on the EN pin, meaning the regulator would not be turned on(it waits until EN hits >0.9V). However it appears the EN pin is connected to the VCC of U4. And U4 is connected only to the pin 13, 14 of the VGA connector! So how would that combination ever work? It looks like U4, drives the EN pin, however, it appears to be the VCC pin of U4 doing this, and surely – this is the power supply for the U4 pin. Perhaps I don’t understand the schmitt chip’s behaviour. This is a different topic to the main question, but it had me wondering as I was thinking things through.

      Hopeful for any help and support, many thanks.

      November 25, 2017 at 1:05 AM #17511
      renegadeandy
      Participant

        Help!

        November 27, 2017 at 5:05 PM #17588
        marqs
        Participant

          If you take a look into schematic, you’ll see that F2 is connected to 5V rail, and EN of U7 to 3.3V rail. If they are both below 1V then your PSU/regulators are not behaving correctly. I’d start by checking 5V rail since it drives 3.3V regulator – maybe D5 is installed wrong way (you should measure 5V over it even when power is switched off) or you have a short somewhere.

          November 27, 2017 at 7:06 PM #17591
          renegadeandy
          Participant

            Hi Marqs,

            Both of those tests pass, 5V rail is fine, as are all regulators.

            November 30, 2017 at 12:55 AM #17667
            marqs
            Participant

              So all regulators and voltages are fine after all? In that case, I’d ensure that the bottom pad of FPGA is soldered properly on the PCB – if it doesn’t have a good contact, an otherwise correctly built board may seem dead.

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