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  1. #21
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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Without a test lamp or similar load, the SCR latched state will be released when the flash bulb is burned out. Any load maintaining a load current above MOC3010 holding current of 100 µA keeps the latched state.

    Mentioning the exact purpose of the circuit had avoided additional queries.

    The 33k resistor value in the post #1 schematic is obviously wrong. It would never trigger the SCR which requires 5 mA gate current.



    •   Alt10th January 2018, 07:45

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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Thanks for the feedback FvM! Ok, my mistake. The 33k resistor was in fact a 33 Ohm resistor.............. My bad.

    But, I am confused by the statement "Any load maintaining a load current above MOC3010 holding current of 100 µA keeps the latched state."? So, in fact the reason that the SCR gate is remaining closed (Even though the high side battery is disconnected) is because there is a load remaining on the MOC?

    I do not understand? How can that be if the output side of the MOC is only driven by the high side load? Should I be using a different MOC?



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    I was previously assuming that the MOC is latching the current, but with sufficient load current it may be the SCR as well with it's holding current of 10 - 20 mA, or both in parallel. You can use a regular opto-coupler with sufficient current transfer ratio instead of MOC3010 opto triac and still have the SCR latching the current.

    But you didn't yet explain why it isn't an option to avoid any additional load in parallel to the flash bulb?



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Thanks for bearing with me. I will see if I have a regular opto-coupler and try that. I am not understanding how to "avoid" additional load in parallel to the flash unit? Sorry.



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Quote Originally Posted by btvarner View Post
    I can understand that I might have something wired in correctly, but what I don't see is how the SCR can still be closed after the battery is removed, and remain so after the battery has been reinstalled? I assume that the MOC truly separates the trigger side power from the flash side power?
    There is something happening here.
    Yes, MOC should isolate the trigger side from the "power" side, in your circuit, the flash bulb side.

    The only plausible explanation is that the opto-TRIAC is triggered always, in other words, the LED triggers the TRIAC all the time which is caused by the "momentary switch"-referring post #1 notation. So, the "momentary switch" does not turn OFF.

    When removing the battery, both TRIAC and SCR should go OFF, so the problem lies in the triggering circuit.



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Ok, I re-tested in the following manner:

    <Initial triggering: (1st shot) as always. Press camera shutter, triggering circuit closes, flash circuit closes, flash bulb ignites. As always, all good.
    <Ejected spent flash bulb from flash. Disconnected flash from circuit, DISCONNECTED BATTERY FROM TRIGGERING CIRCUIT. Then reconnected circuits & new flash bulb.
    <Subsequent triggering: (Second shot). Yea! all worked as it did with the first shot!

    So, it seems that the issue is NOT that the SCR is at fault, but rather the MOC3010M. Why would that be?

    1) I do not see in the datasheet where this component maintains a closed output that might cause this?
    2) Why would the triggering circuit/side maintain power to the MOC LED?

    i am going to replace the MOC with a spare and re-test, NOT disconnecting anything in between shots, just to ensure that this does not solve the issue.....

    This live testing with flash bulbs is killing me. Each flash bulb expended is costing me $1-$3, each & every bulb.......................

    - - - Updated - - -

    Before I put in a replacement MOC, can someone again look at the images in my earlier post & the schematic in the first post, to check if I am missing something? I assume that if this MOC malfunctioned, and I have not fixed the reason why, another MOC will just break also? Thanks!

    - - - Updated - - -

    I went ahead and replaced the MOC. Re-tested, same results. I am at a loss.



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Quote Originally Posted by btvarner View Post
    <Initial triggering: (1st shot) as always. Press camera shutter, triggering circuit closes, flash circuit closes, flash bulb ignites. As always, all good.
    <Ejected spent flash bulb from flash. Disconnected flash from circuit, DISCONNECTED BATTERY FROM TRIGGERING CIRCUIT. Then reconnected circuits & new flash bulb.
    In the tests you did from post #1 up to about post #20, you have always disconnected the battery from the bulb circuitry ?
    This is the first time you disconnect the battery from the triggering circuit ?

    If answer to my 2nd question is YES, then the problem as I suspected is with the "momentary switch" i.e. the shutter. The problem is NOT the opto-TRIAC nor the SCR ! The "momentary switch" stays somehow closed up until you disconnect the battery. After disconnecting the battery, seems like the "momentary switch" opens.



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Hi CataM,
    1) "you have always disconnected the battery from the bulb circuitry?" - In every test I try it first without disconnecting the battery. I just remove the bulb (Which breaks the circuit). When that never works, I then in each test try it my disconnecting the flash side battery (2 D Cells), and that does not work either.
    2) "This is the first time you disconnect the battery from the triggering circuit?" Yes. These last two tests.

    Ok. I obviously do not KNOW that this is correct, but.....
    I have contacted Canon tech support & was even transferred to a Canon engineer. He told me that the internal camera switch is not powered, and is only closed momentarily. In other words, the PC circuit is closed upon the shutter being internally tripped electronically, but it is ONLY a mechanical closed switch.

    I have only a multi-meter. When connected to the PC port & in the continuity test mode it remains at "OL". Before the shutter is tripped. During the shutter trip. After the shutter trip. Never moves. This to me shows that a) the meter is not fast enough to capture the swift closure of the camera switch, and b) There is no closed circuit before or after the shutter trip.

    Therefore how can the left/low circuit continue to be under load if the circuit is broken (Switch open) except for the milliseconds that it is closed during shutter trip. If I am doing this wrong, let me know.



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    After firing the bulb, the current through the SCR should be zero. And the SCR should be off. At this point, measure the SCR gate voltage. it SHOULD be zero. If not, there's something wrong with your triggering circuit. Perhaps when you connect the battery there's a transient that triggers the Triac or SCR. But stepping back a bit, it seems that a fundamental problem here is that you are using a component designed for AC(TRIAC) in a DC circuit. Why did you use a triac output opto instead of a transistor output?

    Warning, stupid question ahead:

    Why didn't you just use the switch closure to drive the SCR gate? The SCR requires 1.5V at 8mA nominal. That might be pushing the limits of the battery, so why not use two transistors to drive the gate?



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Thanks Berry!
    I am going to answer this in a way that will likely make me look stupid, but then I guess I am. Anyway, the current/flow of amperes is measured as zero, but the voltage remains as 3.1V, the amount of battery voltage of the 2 D Cell batteries in the flash.

    I am tending to agree that the triggering circuit may be the culprit, but how do I determine if there is a transient?

    It is primarily designed for AC, however, the datasheet says it can be used DC.....

    Tried a transistor output instead of a Triac. The result was only a partial burn of the bulb. The current was cut off too quickly, resulting in the flash bulb only getting to about 1/2 brightness.

    The last "Stupid" question is in fact the most important! I need to be absolutely sure that the triggering circuit connected to the camera was isolated from the flash. Anywhere you go, looking about information on triggering an old flash bulb flash, using a modern DLSR, results in people who have fried their cameras in doing this. I do not want to ruin a camera I paid $3,800 for, doing something stupid..........



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    The only way you can observe a transient is with an oscilloscope, your multimeter is of no use.



    •   Alt10th January 2018, 21:58

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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Ok, I have been troubleshooting this problem from all angles. I do not have a solution, but I do have what I believe is exactly what is happening. The result is repeatable and predictable. No matter what high side load is used:

    **The MOC3010M output/detector (Pin 4 & Pin 6) remains closed even after the emitter side power is removed** This only occurs after the emitter side of the MOC is triggered the first time. Pins 4 to Pin 6 thereafter remain closed, completing the circuit, and causing immediate ignition of the bulb upon insertion into the flash.

    Now, I thought that MOC3010M's do not behave this way. I am under the impression that the output/detector side of the MOC remains closed only as long as there is power to the emitter. Am I wrong in that belief? I have validated that there is absolutely NO load remaining on the emitter side.

    So, the only method to ensure that the anode/cathode does not remain closed (Thereby completing the circuit) on the NET5465 SCR, is to do the following:
    1) Pull the MOC from the breadboard
    2) Pull the SCR from the breadboard
    3) Reinstall both

    If I just pull the SCR & reinstall, the anode/cathode continues to remain closed. Any suggestions as to what other component I might use in place of the MOC to resolve this issue? Thanks!



    •   Alt12th January 2018, 00:10

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  13. #33
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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    If I just pull the SCR & reinstall, the anode/cathode continues to remain closed. Any suggestions as to what other component I might use in place of the MOC to resolve this issue? Thanks!
    Did you read what was recommended many replies ago ?
    Don't use tyristor for loads tied to DC power supplies, use MOSFET or any other transistor.

    - - - Updated - - -

    Tried a transistor output instead of a Triac. The result was only a partial burn of the bulb.
    ...what means that the transistor was not properly biased in the saturation region, just it.
    --------------------------------------------------------------------------------------------------
    Part of the world that you live in, You are the part that you're giving ( Renaissance )



  14. #34
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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    I reviewed the photos in post #16 and stumbled upon the "test lamp removed point". The test lamp is series connected, there's no current flow without it. I suppose all tests are carried out with the test lamp in place, or with a different circuit. What's the real circuit?

    I wonder if there's some circuit feature inside the flash unit maintaining current flow after the flash bulb is burned.

    I also wonder if the underlying problem hasn't been already solved by other photographs with better electronic skills?

    My general thought is, if the flash unit keeps the SCR and/or MOC3010 in triggered state, one should better use a regular optocoupler and transistor switch in combination with a pulse extension circuit.

    Can we catch an exact circuit schematic of the flash unit?



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Attached is the way I would do this. The values are subject to change; you'll have to figure out what MOSFET to use, what the time delay of the 555 should be, etc. (you should use an LMC555, or similar).



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Referencing Post #34 from FvM,

    1) “Post #16”: You are absolutely correct. I took the last 2 images after removing the test bulb, but before moving the return (Black) wire to where it links to negative & completes the circuit. Sorry, but I do have this in place during testing with the flash unit.

    2) “if there’s some circuit feature inside the flash unit maintaining current flow after the flash bulb is burned”: Absolutely! The circuit inside the Graflite flash unit is closed by two means. Number 1 is the positive & negative leads of the cord connecting from the flash unit into the breadboard as indicated in the images. Number 2, is a flash bulb being inserted into the flash unit.

    This is why the setup functions correctly for the first “flash”, but not subsequently. The spent bulb still keeps the circuit closed at that point, which keeps the current flowing on the breadboard & through the SCR.
    When the spent bulb is removed & replaced, the second the new bulb touches the contacts in the flash, it ignites the new bulb.

    3) “hasn't been already solved by other photographs with better electronic skills?” I whole heartedly agree that I do not have much experience. In fact I have been trying to learn everything I can to solve the problem. There is a catch.

    Ok, this is where the conversation always goes when I am discussing this with people. As best as I have been able to find out, no, it has not been resolved.

    There are a few “solutions” out there for using an old flash, with a new digital camera. Everyone points to these, and says, this will do it. But it does not, and there is a very good reason why. This next couple of paragraphs must be fully read to understand that……..

    Photographers are a small sub-set of the population. Photographers who wish to use OLD electronic flashes on new digital cameras is a very small sub-set of photographers. Photographers who wish to use old FLASH BULB flashes on new digital cameras is so small that it is almost non-existent. The solutions that are found online, are designed for use of OLD electronic flashes, not old flash bulb flashes. There are differences that apparently do not allow the solution for one to be used to solve the other.

    OLD electronic flashes use electronics themselves to close the circuit. They in turn use capacitors or other means to produce high voltage for the flash. Sometimes 250V or more, but the amperes are relatively small. Devices on the market and online designed for these flashes work fine for them. They do not work on a Graflite flash bulb flash. I have tried them. I have even spoken with the companies that produce them, and have been told by them their products are not designed to work, nor do they work with a flash bulb flash.

    A flash bulb flash such as the Graflite only has 3 volts. But as I understand, it produces maximum amperage to trigger the flash bulb. Designed a long time ago, when all switches/triggers were mechanical, the full volts & amps travels through the cord and thereby the switch that triggers the flash bulb.

    So, this is why the many people, over many months have had difficulty understanding why this seems to be so difficult You add in the fact that I am far from an electrical engineer, and this is why I seem to not be able to resolve the issue.

    I have an OLD electronic flash, several in fact. I have successfully used them on my Canon 5D Mk III, which is a professional level camera. I even paid an electronics shop with an oscilloscope to test my most powerful OLD electronic flash. There series of tests produced the following results:

    2-3 Milliseconds = Event Duration
    10V = Average Voltage
    2.1A = Average Amperage (4A Max)

    So I know that my camera can handle this amount directly because I use it. But with the old FLASH BULB flash supposedly putting out up to 9A of current?????? I have heard many horror stories about people ruining their camera trying to do this. I do not want to have my $3,800 camera go down the drain.

    Sorry for being long winded. Just trying to get the details out there. I will answer the other questions a little later. Thank you all!

    - - - Updated - - -

    Hi FvM,
    4) “, if the flash unit keeps the SCR and/or MOC3010 in triggered state, one should better use a regular optocoupler and transistor switch in combination with a pulse extension circuit”. I think that also. How about something like this? I created this earlier and abandoned it before testing. Plus I have all the parts. Obviously the actual cord to the flash unit replaces the 9V battery, and the test lamp is not used at that point.
    Click image for larger version. 

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    5) “Can we catch an exact circuit schematic of the flash unit?”. Here is the overall schematic, from the Graflite Service Manual.
    The “N” Extension is an option I do not use. The opposite end of the cord described at “SHUTTER” connects into the breadboard.
    Click image for larger version. 

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    Hi barry,
    “Attached is the way I would do this” Thanks Barry. I will look into this and see. I believe I posted my last post before I saw your last post. Does that information change your suggestion any? Thanks!



  17. #37
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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Barry, it seems like this circuit is interesting also. Is part of it covered by the oscilloscope window? Thanks!



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    Oops. The part that's cut off is simply a 1k pull-up resistor tied to Vcc, and the vcc connections for the 555.



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    have you killed the deive with too much gate current? such that it is always on?



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    Re: Why Does The NTE5465 SCR In My Circuit Remain Closed, Even With No Current?

    No, the reason I know this is because once everything is disconnected, then reconnected, the circuit works as designed for the "first shot". Only after it is first triggered, does it thereafter remain on. I have a more detailed explanation of those actions in a previous post.



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