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Re: [OM] Flash Problem/Technical Question

Subject: Re: [OM] Flash Problem/Technical Question
From: "John A. Lind" <jlind@xxxxxxxxxxxx>
Date: Sun, 02 Mar 2003 23:42:01 -0500
At 01:04 3/1/03, you wrote:

On Sat, 1 Mar 2003, John A. Lind wrote:

> Any clues as to what's going on and why OM-4/OM-2S won't trigger it will be
> very much appreciated!

The OM-4/2S flash trigger is driver by an SCR instead of a mechanical switch.
Perhaps the circuit needs a minimum load present in order to operate and your
little device may not provide enough load.  I'm not familiar enough with the
circuit to say for sure, but it's something to consider.
                                -mark

Mark,
Thanks for your reply . . . this is along the lines of what I suspect, as the unit works with mechanical flash triggering (e.g., OM-1n).

If this is the case, is it possible a resistor on the order of about 220 to 1k ohms in series or parallel with the flash contacts resolve this (create enough "load" when the OM-2S/OM-4 fire)? With a low trigger voltage of barely over 6VDC, the unit undoubtedly has some form of circuit through an SCR [??] or TRIAC [??] to present a low voltage on its contacts.

I also found a couple of simple circuits for optocoupler triggering. One only has four components, but I'd rather keep this as simple as possible and not rip the thing completely apart to reverse engineer its circuit . . . although I'm thinking that may be the only way out.

Thanks,
-- John
PS: Since I've discussed possibly opening up an electronic flash . . .
Anyone thinking about opening an electronic flash up should be knowledgable about how to safely and properly discharge high voltage, high capacity capacitors . . . and verify they are, indeed, discharged . . . before working around them. Even with this very low powered unit (in Watt-Seconds of IR output), I have little doubt there is a 300VDC to 500VDC electrolytic with enough capacitance in the hundreds of uF range to kill under the right (wrong) circumstances. At that voltage and capacitance, it's more than enough energy. I've been "zonked" across a room by over 500VDC and was very fortunate the source was such low current capacity and my contact with it was for such a short time (milliseconds) that I lived to tell the tale. Even so, the experience was definitely no fun and I was in some pain for a while afterward.


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