The aim of this project was to add manual power adjustment without removing the original auto functionality of the flash. Existing mods involve removing the light sensor and replacing it with a variable resistor or a series of switched resistors (Erwin Stock provides a good writeup of this mod here). This allows manual control over the output but removes the flash’s auto capabilities, reducing it’s usefulness as an on camera flash.
This is an improved version of Erwin Stock’s manual power mod which keeps keeps all of the original functionality intact. The overall principle is the same but a 3.5mm stereo socket is used to switch the light sensing phototransistor out of the circuit only when the resistor box is attached.
Safety & Disclaimer
Electronic flashes operate at high voltages and can hold a potentially lethal charge even when turned off. Do not attempt this modification unless you are familiar with the necessary safety procedures and are able to make the equipment safe before proceeding.
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|1||Knob to fit rotary switch|
|2||3.5mm stereo socket with break contacts|
|1||3.5mm stereo cable|
Remove the 4 screws on the underside of the flash head holding the upper housing of the head in place. The upper housing should now lift off. The front window assembly is held in place by the upper housing and should be temporarily secured with tape to prevent contamination of the tube and reflector.
Connect the tip break contact and middle contact of the 3.5mm socket together. This will reconnect the phototransistor board when nothing is plugged in.
Connect the outer contact of the 3.5mm socket to the same solder post as the black wire on the metering board (upper PCB, “Automatik-Leiterplatte” on the circuit diagram) . Do not disconnect the black wire.
De-solder the green wire from the opposite side of the metering board and connect it to the middle contact of the 3.5mm socket. Connect the tip contact of the 3.5mm socket to the solder post the green wire was originally attached to.
External control box
Solder the resistors to the rotary switch as shown in order of highest to lowest value (see circuit diagram) with one end connected to each contact and the free ends connected to each other
Connect the tip contact of the 3.5mm socket to the centre of the rotary switch.
Connect the middle contact of the 3.5mm socket to the rotary switch contact that will act as the auto setting.
Connect the outer contact of the 3.5mm socket to the joined ends of the resistors.
The best place for the socket is on the back of the head to the left of the hinge where there’s plenty of space between the PCBs (also it’s unlikely the cover will go back on if it’s anywhere else)
The flash will operate normally when nothing is plugged into the 3.5mm socket or the external control box is set to auto.
When using the manual power settings the most powerful auto setting (narrowest aperture) must be selected on the flash head