Quick question. I’m in the middle of modding my Q8 to XHP50.2’s but have hit a snag. The reflow was going absolutely fine and all seemed well. Once it was done I used a multi meter to check the LEDs were all working using the + and - pads on the MCPCB. All lit up, lovely. But then as a matter of course I always check continuity over the MCPCB, between + and the underside, and between negative and the underside. To my surprise, my multi meter beeped when I checked between - and the underside! The led4power Q8 MCPCB has 4040 footprints also, so to double check I tried between - and the thermal pad, yup, beep. I have another led4power Q8 MCPCB so I checked that, no continuity between - and thermal pad. I then checked another DTP MCPCB that had a xpl hi flowed on and that doesn’t give continuity between - and the underside.
So I took all 4 XHP50.2s off the board expecting to see a tiny bit of solder from the - to thermal pad, nothing. Reflowed again, tapping each LED to squeeze out excess. Same result!
My question is, is it normal for the XHP50.2 3v to make continuity between - and the thermal pad once flowed into a board?
I thought it would be best to check before I put it in the light and melt something!
No, it is not normal and you do still have a solder bridge between a minus-pad and central pad somewhere. So desoldering leds, check and re-soldering them until the bridge is gone is the way to go I’m afraid.
A unlikely option could be a faulty board, in that case the continuity between minus and core is still there without any leds.
Ok, thank you! Glad I checked before I installed it. I did the reflow three times in the end with the same result. So I shall remove the LEDs, check to see if the board still has a short, and go from there.
So, just taken all the LEDs off, still getting continuity between - pad and thermal pad! Go figure!
Ok, I’m an idiot! I feel like asking for this thread to be deleted! Haha. So it turns out that the helping hands device thing I was using had scratched a tiny tiny bit off the top of the board, causing a short between negative and the underside. Lesson learned and hopefully it might help someone else out 
I hope the the final reflow goes well and that you get the Q8 XHP50 beast to work!
At least you did figure it out.
Got it all together and working last night. Rough ceiling bounce numbers:- before 860lux (with bypassed springs so around 6k lumens), after 2000lux, so around 14k lumens. Happy with that!
I got the XHP50.2s from sofirn, they’re listed as 5300-5700k. I didn’t know what to expect, but they’re noticeably warmer and nicer than the ones in my Lumintop FW21 Pro.