Chuck wrote:
>>
Tim never did respond to tell us what was going on with those diodes.
<<
Ok , I only just now caught my name being used in vain!
The reference mentions soldering wires to short out the diodes inside.
Since that is all that was said, and I don't have a schematic, I can only make
an educated guess here:
Ideally the slave needs to trigger either a positive or negative polarity
strobe flash unit, so as to operate with different camera vendor's devices.
(The OM flashes are all positive polarity) Conventional transistors (or scr's)
only conduct well in one direction or have other limitations when operated
inverted. It is likely, that the slave unit has a diode bridge or other series
diode arrangements to allow it to trigger both positive or negative devices.
The diodes add at least 0.6V and maybe 1.2V drop (4 diode bridge). Quite often
a small low power SCR is used as output switch in the slave, to pull the flash
trigger pin low. These drop about 1V when "on". So potentially the output only
gets pulled down to 2.2V above ground, instead of ~0V. This may be above the
threshold at which the strobe triggers correctly. This is particularly true if
the slave-trigger steals it's power from the flash trigger pin. It then starts
off lower than normal or even below the trigger level.
Many
newer flashes have extremely small currents required to trigger them, and
stealing current from the trigger pins may stop them working altogether.
Remember also, some new flash units have unloaded voltages as low as 4V.
Regards,
Tim Hughes
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