LED Strobe Trigger for Olympus OM-D E-M1 Mark II

by vsc2

3.9K1022

Intro: LED Strobe Trigger for Olympus OM-D E-M1 Mark II

The Olympus FL-LM3 on camera strobe is used in an underwater housing to trigger external strobes (e.g. Sea&Sea YS-D2) via fiber optic cables. The recycle time of the FL-LM3 can be as great as three seconds if the flash dumps all of the charge on its photoflash capacitor into the Xeon tube. On the other hand the YS-D2 has a recycle time at least 50% shorter than the Olympus strobe.

Given that the FL-LM3 is only used as a trigger for the external strobe, there is no need for a Xeon tube with its high output power. This modification substitutes a pair of high brightness red LEDs for the Xeon tube. The net result is that recycle time is limited by the communication protocol between the camera and strobe, or about 10 fps. Otherwise full TTL capability is preserved given the LEDs emit light pulses of the same duration which the native Xeon tube emits, including pre-flashes necessary for TTL operation.

STEP 1: Disassembly

Remove the four torx screws from the base of the strobe.

Between the rotating / tilting strobe head and main body are four screw covered by black stickers. Remove the stickers and screws. A knife at the edge of the sticker works well for removing the sticker without damage, or you could just pierce the center of the sticker if you plan on disposing of them. Store the sticks for reuse on a sheet of wax paper.

On the strobe head is a sticker that runs almost the width of the head. Remove this sticker and two screws that are hidden.

Remove the foot of the flash, side of the main strobe housing and separate the two half of the head just enough to remove the diffuser / reflector assembly with Xeon tube attached.

STEP 2: Remove Resistor

A 750K ohm surface mount resistor must be removed to disconnect the photoflash high voltage from the IGBT.

A hot air rework tool can be used, or a soldering iron with a little more work.

STEP 3: Remove Connections to Flash Tube and Trigger Transformer From Main Board

Disconnect the wires that run from the main strobe circuit card to the strobe head. These connections are to the Xeon tube and trigger transformer within the head. They are reused for connection to LEDs which will go into the strobe head.

STEP 4: Replace the Photoflash Capacitor With a 1 UF 350V Standard Capacitor

This step is optional. Given that the IGBT / Xeon tube is never allowed to discharge the photoflash capacitor, recycle time is not an issue thus the size of the photoflash capacitor is not relevant. Though the initial charge time with a 1 uF capacitor is almost instantaneous.

STEP 5: Attach the Base of the 2N2222 Transistor (LED Driver) to the Gate of the IGBT

The heat shrink assembly to the left of the image contains a 2N2222 transistor and resistor to set base current. One side of the resistor is connected to the gate of the IGBT device using 30 gauge wire.

STEP 6: Connect to +3.3V and Ground

Connect the 3.3V and ground connections to the main card using 30 gauge wire wrap wire.

STEP 7: Remove Xeon Tube and Trigger Transformer

From the strobe head remove the Xeon tube and trigger transformer. The reflector is not used and can be discarded.

STEP 8: Attached LEDs

Form the leads of the LEDs and attach to wires that route between the main strobe body and head.

STEP 9: Drill Two 5mm Holes for the LEDs and Epoxy in Place

In the diffuser assembly drill two 5mm holes for the LEDs. Note that the edge of each LED coincides with edge of the opening to the diffuser. The LEDs are centered top to bottom on the diffuser.

Positioning of the LEDs in the diffuser is important given they need to be positioned behind the fibers when the strobe is mounted to the camera body and the body is in the underwater housing. Try to be as accurate as possible.

Use a small bead of epoxy between the diffuser and LED, on the inside of the assembly.

STEP 10: Reassembly

Reassemble the strobe. If a smaller capacitor is used in place of the large photoflash capacitor, use foam or another similar material to fill in the void such that the smaller capacitor is not left to rattle around inside of the strobe body.

STEP 11: Test


STEP 12: LED Driver

The LED driver and LEDs is a very simple circuit as shown. Note that there are no series resistors inline with the LEDs. The pulse duration is very short thus peak current is within what the LED can dissipate. We need a lot a photons to drive the fibers, thus this approach was adopted.

STEP 13: Olympus Reference Schematic

For reference this schematic shows the portion of the Olympus strobe pertaining to driving the Xeon tube. A traditional IGBT based design is used by Olympus.

STEP 14: Bill of Material

1 - 2N2222 transistor

1 - 10K ohm resistor

2- High brightness red LEDs

High brightness LED specification: 12000mcd, 8 degree viewing angle. Multiple sources exist, where one possible supplier is SuperBrightLEDS.com part number RL5-R12008.

14 Comments

scalesweb 1 year ago

.. also can you confirm any other part numbers for the LED's such as digi-key, mouser and uk-rs.online or Farnell?
Kind regards
Richard

vsc2 1 year ago

Sorry for the late reply. The components are largely available from any of the sources you cite where have used Divi-Key, Mouser and Farnell in the past. That said the LED which I specified now shows up as discontinued, but still available at a clearance price at superbrightleds.com.

One thing to consider is that alignment of the strobe in your housing relative to the ends of the fibers is more critical than the OEM's strobe. Said another test firing above water is prudent, but more so given the necessary narrow field of regard for the LED (e.g. required to provide sufficient drive to the fibers).

Clearly a photoflash capacitor is one of the common failures in flashes, but it's hard to say what went wrong. It's an easy test once you get the unit apart, though stay safe given the high voltage.

scalesweb 1 year ago

Hello and thank you for your reply. I am going to have a go with these: https://uk.rs-online.com/web/p/leds/9120585/
They are similar but a little brighter and a wider viewing angle (maybe the wider viewing angle offsets the greater brightness?).
I'll report back ind due course.

vsc2 1 year ago

Wider angle nominally means the light at any one point is less given the spread over a great field of regard. Higher intensity might compensate. That said a wider field of regard can only help with alignment with the fibers.

scalesweb 1 year ago

... also - could I substitute an MPSA42 for the 2N2222 - I have a bag of MPSA42 - both are described as NPN Bipolar Small Signal Transistor - I use MPSA42 for switching applications - driving Nixie tubes etc.
I have some 2.2uF 400V caps on hand though I stupidly failed to recall which lead was connected to which side of the cap - is it Grey>Negative - or the other way around?

vsc2 1 year ago

For some reason I can't find your 2N222 question on this site. Looking at the MPSA42 versus 2N2222, the drive required for the higher voltage device (MPSA42) is a factor of 10 larger. That said the I suspect the chosen resister in the base circuit is likely a small enough value. And if your MPSA42 doesn't work, you can easily swap it for a 2N2222.

scalesweb 1 year ago

Many thanks - I shall see what happens - I thought I asked this also but don't see it now...: Can you confirm - for the 1ufCap - is the Grey lead connected to the negative (I removed the photo flash cap and failed to record that detail!)?

scalesweb 1 year ago

Hello, I came across this during a frenzied search for anything that might help me breathe life back in to one of these. Just returned from a dive trip with my wife and herFL-LM3 failed after two weeks of use (probably 500 activations each day).
I am a keen electronics hobbyist so your mod should not be an issue.
Can you advise in the first instance - is it the CAP that fails generally - and if so - for a quick fix - should i try just replacing that?
... or perhaps I should man-up and implement your solution!
Kind regards
Richard

MrFebtober 2 years ago

This is great, thanks for posting this project! I hope I can perform the same conversion on the FL-LM2 flash for my E-M1 mk 1!

tsangh 5 years ago

Thanks for the instruction!

Finally .. completed.

Tested successful on my OM-D EM5 Mark II with SEA&SEA YS-D2.

OneSharpChisel 5 years ago

Any chance, without too much thought, would you suspect the procedures would be similar for the Olympus FL-LM2, which can be obtained much cheaper?

Thanks for a great instructable, I've been thinking about this for years, just lack the knowledge to pull it off!

vsc2 5 years ago

When I owned a E-M5 with that strobe all I modified was to force it to flash in the down position without programming a button for underwater mode. That said this question came up but a full solution was not published on WetPixel, where I started a thread on this modification for the E-M1 mk II's strobe.

http://wetpixel.com/forums/index.php?showtopic=600...

That said I believe the basis to start such a mod is in the last few posting in the thread cited. In my case I found a used strobe in good condition to modify. As I recall the FL-LM2 on the used market is very low cost.

You will find the hardest problem if you don't have the tools or experience working with fine pitch component is in fact soldering. Though there are many tutorials on the web, where practicing on something else would be a good starting point.