An Improved Metz 45 CT-1 Manual Power Mod (with auto)

Introduction

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

WARNING

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.

Standard disclaimer

THE INFORMATION IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE INFORMATION ON THIS PAGE OR THE USE OF OTHER RELATED PAGES AND LINKS.

Materials

Qty Part
1 Rotary switch
1 Project box
1 Knob to fit rotary switch
2 3.5mm stereo socket with break contacts
1 3.5mm stereo cable
heatshrink
wire
 1 2.2M resistor
 1 56K resistor
 1 22K resistor
 1 15K resistor
 1 10K resistor
 1 5.6K resistor
 1 3.9K resistor

Walkthrough

Disassembly

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.

Wiring

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.

Before:

right side - before

After

right side - after

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.

Before:

left side - before

After:

left side - after

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

resistors

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.

control box

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)

socket installation

Operation

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

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