I too have found the ttl consistently underexposes. I've currently got my camera set at +2 EV and I never get a full dump on WA shots. Macro is pretty good, but still usually underexposed. I've got my camera set for subject + background. I've tried my YSD-1's at the 0 setting, as well as bumping them on the plus side all the way to max..
I tried D500 in Nauticam housing with that TTL circuit and YS-D1 strobes. TTL accuracy was normal. No any correction was needed shooting at "0 EV". The same good result i had in land tests.
I think, you have something wrong in your setup. Evaluate carefully each component of your system to find what is wrong.
Specify the details:
1) Do you use fiber cable exactly #26212 or any other product number? Do you have one more same cable to change it for test?
2) Do you use ENELOOP batteries in the strobe?
3) Check, if you strobe is in "DS-TTL II" mode.
4) Check TTL-Converter onboard switches for YS-D1: OFF, OFF.
5) Check your camera settings to be sure that you shoot inside the working range of TTL flash.
Yes, TTL board also may be defected, why no. Then you need to change it. But first of all check all other components in your system and settings, the wrong setup happens more often.
Use one strobe to clear the land test. I recommend the following camera settings: max sync speed (by menu) - 1/200 (without "Auto FP" !!!), ISO 200, Shutter speed 1/200, Aperture F11....F16 for WA shooting at distance about 1.5-2m and F16...F22 for Macro at distance 0.4...0.5m. Such parameters point situation to the middle of YS-D1 TTL flash range, easy to make tests.
Pay attention, that YS-D1/D2 strobes have rather narrow optical TTL range in themselves (only 0.63 ms burning time is available for optical TTL control). This is less than 50% of YS-D1 power. If you need a power more than 50%, you must control it only manually or by electric input. Just for information: YS-D1 full burning time = 4.2 ms. But only 0.1-0.63 ms range is available for TTL control.
Camera and TTL-Converter work normally , they increase signal for flash more than 0.63 ms when necessary (up to 4.2 ms), but YS-D1/D2 strobe does not respond by increasing power more than 50% limit. This is undocumented feature of YS-D1/D2 strobes. And this is explanation why sometimes you set even +2 ev at camera but don't have enough lighting, - because more than 50% of YS-D1 energy is unavailable.
By the way, the other strobes on the market don't have such restriction, they are very good for TTL. For example Z-240 full power range (0.01-3.2 ms) is available for optical TTL control, it has no any restrictions.
So, if you want to shoot maximally effective with TTL, the best choice: Z-240, YS-250, DS-161.
Edited by Pavel Kolpakov, 21 November 2017 - 11:06 AM.