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What to do when A HMI fails to strike.

By Procam Take 2's Head of Engineering, Hugo Santos

This is a reoccurring fault that can be dealt with in the field but also one I fix here at Procam Take 2 repeatedly. It can happen across the ARRI HMI range.

The HMI may be working brilliantly at the start of the shoot; you break for lunch and save the lights. You come back to set, strike up, and the 1.2K HMI will no longer fire up.

So, you troubleshoot. First, you check the bulb; you may even swap one bulb for another. Check if the head switch is in the ON position, check if the header cable pins are not pushed in or bent, and make sure they connect easily.

There is power to the unit, but it will not strike.

A prevalent issue with HMIs is the micro switch on the head.

The micro switch acts as a safety device. The lamp head will not turn on if the door is open to prevent people from being injured or blinded by looking at the exposed bulb if it were to strike without the Fresnel in place.

Here’s how to check the microswitch:

On standard HMI heads, the micro switch is located here

ARRI HMI Microswitch


There is a spring inside the microswitch. When the door is closed, this switch is activated, and it will communicate to the ballast saying, “it’s safe to turn on; my door is not open”.

The easiest way to test if this is working is by pressing the microswitch in with your finger.

With the other hand or a partner, press the on button on the ballast side for 1 / 2 seconds. If the light inside the switch comes on, this means that the microswitch is working electronically but not mechanically.

The micro switch may have been forced too far out, or you can have a lot of slack in the door where it meets the switch, so by the time you close the door, the micro switch won’t be activating anymore.

Usually, there is a little grub screw holding the micro switch tube in position.

ARRI HMI Grub Screw


Undo the grub screw, slide the tube slightly towards you and re-tighten it.

Test the light, if it is still not working adjust as necessary until you get the head to strike and once again you have light!

Procam Take 2's Repair and Service Centre has the facilities, knowledge, and expertise to service and repair commonly used grip and lighting equipment from leading manufacturers, including ARRI, Kino Flo, Sachtler, OConnor, Dedolight and Litepanels.

From troubleshooting to complete repairs, our engineers understand the fast-paced nature of the industry and the importance of quick turnaround times. We offer competitive pricing and ensure your equipment is returned clean and in excellent operating condition.

Visit our Repair and Service Centre page to find out more and get a quote.

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