Problem with 4N25s (on V3)

Forums General Questions and Comments Problem with 4N25s (on V3)

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    • #5822 Reply
      John Jensen

      Recently built a V3 for my Wife, and all was good and merry times where here.
      Then she started using it…

      I have narrowed the problem down to this:
      Symptom, the flash triggers twice within 2-3ms creating ghost images of the drops, 1 out of 3 times.

      I took my 20$ scope to the input of the 4N25 to check for multiple pulses there, but nothing, clean sharp signals going into the 4N25. I tried putting another 330Ohm resistor in parallel with the one allready on the input, doubling the power going into the optocoupler, didn’t help either.

      The problem is the same across the board, all three flash ports are showing the same behaviour.

      This does not occur on the V2 she has been using for the last couple of years, so she’s back with that for now.

      Do any of you have an idea what can be going on? I mean there is a perfectly good signal going into the 4N25, and iffy switching going out.

      Please help me get the sweet merry times back 😉


    • #5827 Reply

      The trigger part of the circuit is the same for the V2 and V3 dropControllers. The only real difference between the two is that the pins moved around.

      Off the top of my head the only things I can think of are:
      1 – the flash pulse time may be slightly too long
      2 – one of the flash guns is developing a problem.
      3 – faulty 4N25s.

      1. Flash pulse time
      I have a very old flash gun where if the trigger signal is kept high it keeps firing. To use this with the dropController I have to reduce the trigger pulse time to around 10ms (this flash is the reason the dropController allows you to change the pulse time).

      2. One of the flashes is developing an issue.
      I have a set of Yonhnuo YN560-III’s and one of them starting firing slightly late which causes a ghost image as you describe.
      Although you don’t say how many flash guns your wife is using I suspect it is more than one and this is the issue. 2-3ms is likely too quick for a flash to repeat fire and it does sound like you have one that is firing late.
      This would not explain why V2 works and V3 doesn’t unless different flash guns are used.

      Is the ghost image darker than the main image?

      3. Have you checked the signal coming out of the optocouplers? This is a long shot but you never know.

    • #5847 Reply
      John Jensen

      Hi Martyn.

      My thoughts exactly, and there’s really not much going on after the optocouplers.

      1. My thoughts as well, but it looks like my flashes (Godox tt685) triggers on a flank or something, the pulse can be ridiculous short, but it would still doubletap. (Yes, past tense :-D)

      2. 4 Godox TT685, I tested each individually, and trust me at low output, these suckers can cause epilectic seizures. it might be 5 ms, judged by the drop having moved 5-6 cm between each flash, and yup everything worked just nicely after switching back to the V2.

      I managed to kind of fix the problem, although I still don’t know what was wrong, I was planning to make a breakout board for the optocouplers, as I wanted to double the camera connector, so I did just that, wired it quickly into the V3 and problems just went away. I’m still not sure what could have caused it, but happy times are here again 😉

      Thanks again for a great design!


    • #5873 Reply

      Good to hear you have it working but I am still puzzled by this. I have just tried a view things on one of the test devices I use and cannot duplicate your problem. I purposely kept the circuit as simple as possible so problems would be (should be) easy to trouble shoot yet I now have no idea…

    • #10160 Reply
      Paul Rattray

      I am using a Godox AD360 and seem to be experiencing the same problem, every now and again i have the flash firing twice. It might do this a few times then back to normal, then back to firing twice?

    • #10162 Reply

      How quick is the repeat fire?

      If it is very quick, try reducing the trigger signal time to around 35ms.

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