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Great... I'm stuck with a pair of made in China Sea&Sea strobes... Back to the original question. Point in fact I never got a white LED to work with the YS-D2. In fact I tests a range of different color LEDs settling on red. While I only had Sea&Sea fibers to work with one fiber simply put transmitted far less light, where I couldn't get reliable operation. If I had known at the time I purchased it, it was have gone back for a replacement. That said so much light is coming out of the Xeon strobe that I never noticed the issue until moving to an LED design. My guess is that if you use a similar LED to what I picked and Sea&Sea fiber, the trigger will start working.

Perhaps you looked at my thread with respect building a LED trigger out of an Olympus strobe. That said I'm rather sure that I didn't discuss LED choices, but I found that the Sea&Sea strobe is more sensitive to a red LED than white. Also you need everything working in your favor such as good LED / fiber alignment such that you don't waste energy. Also the transmissivity of the fiber is critical, where defective fiber clearly became a limiting factor. I might not have discussed the drive on the LED needs to be quite large, which is acceptable given it is running in a pulse mode. This to get as much light out as possible. Finally a higher output LED is nominally a smaller field of regard, which makes alignment all the more critical. But this way you get more light down the fiber than if the lens on the LED presents a wider beam. Sorry for the rambling but I'm off doing something else at the moment...

That was my findings as well. That said on the subject of LED triggers, if you need a means to couple the camera to the strobe then a TTL LED scheme might as well be the solution. On the other hand if one is replacing an on camera strobe with LED, in many cases the result might be worth the cost. With an Olympus the recycle time is 3 seconds. The YS-D2 recycle time is 1.5 seconds, max. Is 1.5 seconds worth it? In practice I certainly have found cases where I screwed up and needed to shoot again immediately. Sometime 1.5 seconds made the shot and in many cases not so much. And with respect to power savings on the camera's primary battery, for the M-1 mk II, it doesn't matter given a battery lasts two dives of 100+ minutes with a lot of reserve left. This from someone who spent a lot of time making an LED solution work on the mk II a year ago and used the result during a lot of diving in 2016.

It has been almost a year and I posted an improved version of this underwater housing leak detector using a newer version of AdaFruit's Trinket which is based upon the Atmel SAM processor. The result is a multi-year battery life with a single CR2032 battery. https://www.instructables.com/id/IMPROVED-UNDERWATER-CAMERA-HOUSING-LEAK-DETECTOR/

Late to the discussion.... I understand you are using a Sea&Sea fiberoptic cable. Point in fact I have come across instances of their cables which have significantly lower transmissivity thus limiting the amount of light transmitted to the strobe. In fact by simply holding one end of the fiber up to a light (e.g. table lamp) and looking at the opposite end, you may very see that less than 100% of the fiber is illuminated. In my case I was forced to swap out the dim fiber. The above occurred when I was developing the fiber optic trigger for the Olympus E-M1 mk II, in conjunction with the YS-D1 and YS-D2.

Somehow when I did a search I didn't come up with the P4006... I'm sure you found the correct data sheet. I believe you can follow a similar modification path using what I have documented. The gate of the IGBT, pin 4, is used to drive the LED driver (e.g. bipolar transistor). Removing the resistor marked 753, disconnects the high voltage from the IGBT as well as prevents charging up the capacitor used to drive the trigger transformer. Finally I swapped out the photoflash capacitor for something smaller though this is more cosmetic than anything else. The photoflash cap is never discharged thus the size of the capacitance is not relevant. Though it did make more physical room in the strobe by putting a physically smaller cap in place of the larger Olympus cap. What remains is to figure out where to pick up +3.3v and ground. You might need to use an ohm meter and trace from the hot shoe to the circuit card to find suitable points to solder wires. The strobe I modified had wires going through a rotary joint, thus I used the existing wires. Your pictures show you can simply disconnect the strobe tube CCA and hook up the LEDs with whatever means makes sense. Overall the hardest part of doing this mode is getting the LEDs positioned correctly behind the fibers. I started out with using Kapton tape with piercings to hold the LEDs with the strobe partially assembled. Once I found the right positioning I drilled the strobe diffuser to match the test LED position. I'm sure other schemes are possible to judge the correct LED position.

I'm trying to read the part numbers from some of the devices on the boards. The (IGBT) transistor that is used to trigger the strobe tube in the newer product is a RJP4010AGE (nominally marked as R4010 on the package). That device is from Renesas where their catalog shows they also over a 4009 IGBT. Perhaps you can look to see if one of packages with 8-pins is marked with either 4010 or 4009. The idea used in my original posting, it is grab the signal going to the IGBT switch and use that through a transistor suitable to drive an LED. In short the IGBT works fine for the strobe tube with the very high voltages involved but is difficult (impossible?) to make work with an LED operating at a few volts. The data sheet for the 4009 is, https://www.renesas.com/ko-kr/doc/products/transistor/002/r07ds0370ej_rjp4009ans.pdf

When the Olympus FL-LM2 flash is used with the Olympus housing, it must be in the down position to fit within the housing. In turn normally this means that an underwater mode, consuming a function button, must be set on the body to enable the flash to fire in the down position. It is possible to modify the FL-LM2 to think that it is in the up position such that the flash will fire independent of the position of the flash head. On the main circuit card there are two solder pads in the upper left hand corner (as shown in the attached picture), where moving the black wire over to the pad with the red wire is the one change that accomplishes this modification. There is another thread on this forum with respect to modifying the flash capacitor for the FL-LM2, where the authors detail how to disassemble the flash. In short remove the black adhesive coverings on the screws and remove the screws.

I just got back from two weeks of diving where the E-M1 mk II rig was in the water for dives averaging 90-120 min of bottom time. With the standard Olympus strobe mounted to the camera, I found that I still had 55-60% of the camera's battery life remaining after two such dives. Thus from a battery savings perspective the LED modification most likely doesn't make sense. Point in fact with the mk II, once it was sealed for the day I kept going and left well enough alone. The YS-D2 strobes recycle time specified by the manufacture as 1.5 seconds maximum with Enloop batteries. While it is easy to show much quicker recycle times above water, thus permitting a rate of multiple frames per second, underwater at nominal subject ranges the loss through water is sufficiently great that I found it difficult to get the YS-D2 recycle time to under a second. On the other hand the Olympus strobe takes three seconds to recycle, which seems like eternity at times. The from this aspect the benefit is an overall recycle time of ~1 second. Clearly sometime this makes the shot. Note that the YS-D2 recycle times would be shorter in macro photography but there are few instances where this makes a difference and in those cases I normally use a different method to get the subject into view.

It is hard to say given these pictures given enough of the circuit card is obscured by the black tape. That said I strongly believe something similar could be done given most strobes use more or less similar implementations (e.g. IGBT, etc).

The forum was (is?) not sending me updates on this thread. Perhaps my changes to the settings fixed that, but I'm not confident that what I changed will resolve the problem. And it isn't a spam email filter issue either. With the camera cited in my original posting, with the Olympus housing, I found that the body can be rotated in the housing sufficient to upset the LED / fiber alignment such that the light emitted from the a fiber is insufficient to trigger the strobe. One of the two strobes in use was out of commission for the dive. This only occurred once where I found out in the process of shooting pictures of a pair of frog fish. Switching to an overhead strobe position with the remaining functional strobe yielded good shots... Actually very good shots to the point that I need to use that strobe position more often. Normally I test the rig, shooting a frame or two, but I got lazy that day. It appears I also got hurried installing the camera into the housing. As such as part of setting up the rig look into the fiber mounting holes to ensure you can see the LED's in the center of the holes and/or shoot a frame or two ensuring your strobes fire. A standard strobe with its diffuser and much higher light output would never have this issue.

I must admit a few weeks ago getting the enclosure wet for the first time, at 100 feet the leak detector sounded. In short a small fiber, most likely from a lens wrap, was on the main o-ring. I missed it. That said there was only a few drops of water in the bottom of the housing and the leak detector picked it up doing its job. The fact that there is an audible alert ensured that I immediately reacted to the situation, heading for the surface. That said after rinsing out the enclosure and in theory drying it, I locked it up for the night without desiccant. At some point in the middle of the night the alarm went off again. It would appear enough residual moisture was present, most likely between the wires and the heat shrink tubing used at the end of the sensor circuit board. Note I updated the firmware on Instructables to include a power savings mode which should extend the battery life to a year of standby time. The leak detector in the power savings mode polls the sensor every four seconds. When on travel, test at the start of the trip. The detector shifts to polling the sensor once per second, shifting back to power savings mode after two weeks. The older source code file is still present on Instructables which should yield three months of continuous monitoring (e.g. once per second polling), using a CR2032 battery. The updated file is what was in use when the small flood occurred, thus I'm rather sure the code is working.

A number of DIY leak sensors have been published over the years where SparkFun published a project in 2013 based upon an Arduino. This project builds upon the SparkFun design using an AdaFruit Trinket and a few other components. The following is a link to the instructions for this project, https://www.instructables.com/id/Underwater-Camera-Housing-Leak-Detector/

An older thread discussed modification of an Olympus flash to reduce cycle time and battery consumption. While the results were mixed, I was motivated to create a functionally equivalent solution for the Olympus OM-D E-M1 Mark II without any limitations. Using an Olympus FL-LM3 flash I substituted LEDs in place of the Xeon tube, enabling triggering an external strobe (e.g. Sea&Sea YS-D2) preserving TTL functionality while reducing cycle time and battery consumption. Micro 4/3's cameras use a serial protocol between the camera and flash which is closed to the public. Looking at the bit stream I quickly decided it was a waste of time to reverse engineer the protocol and turned to simply modifying the Xeon strobe subsystem of the flash. In short remove the Xeon tube, trigger transformer, disable the discharge path for the photoflash, substitute a small (e.g. 1 uF photoflash cap) for good measure and add a LED driver and LEDs. The FL-LM3 is a traditional modern strobe using a IGBT to not only drive Xeon tube, but also the trigger transformer. Stop the strobe as part of TTL metering, the IGBT device is driven into pinch off, thus quenching the Xeon tube, leaving whatever charge is left on in the capacitor. This enables the flash to emit pre-flashes, as well as the main flash. By connecting the LED driver to the IGBT's gate, the LEDs emit exactly the same duration light pulses as would have been emitted by the Xeon tube preserving the pre-flashes, etc. The following is a link to the instructions for this modification, https://www.instructables.com/id/LED-Strobe-Trigger-for-Olympus-OM-D-E-M1-Mark-II/ Also a link to a video showing an E-M1 Mark II in an Olympus housing with the modified flash, triggering a Sea&Sea YS-D1 running at frame rate limited by the communication rate between the body and FL-LM3. Note this is somewhat of a trick given if the YS-D2 recycle time increases the frame rate must drop, but there is no feedback to the body. Thus setting the body to run at a lower frame rate is the path forward.

Sorry for somewhat hijacking the thread, but showing my ignorance but what is the possibility of using the Inon EP02 dome port with the Panasonic 8mm fisheye?