Hi I bought a sofirn c8 f three XP-L leds. And modding it with three SFT 25R on a new MCPCB 3535. It have a good contact between + and.- But when I install the flashlight, it only works on the highest mode. when i put back the original MCPCB 3535 ( 3x CREE XPL HD V6) it works fine. I have mode many sofirn c8 f with diffrents leds 3535 sst 20, Osram KW CSLNM1, Osram KW CSLPM1. And all has work with originale driver. What can bee wrong this time? Best regards Thomas.
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Sounds like a short which results in basically direct-driving it. Make sure your solder connections are not able to touch the underside of the reflector, nor bare wire or solder to anywhere on the MCPCB except for the intended pads.
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Check continuity from - to the MCPCB.
There shouldn’t be any continuity.
My guess is you have a bridge between the - and Center Thermal Pad on the MCPCB.
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Hi again. Thank you for your response. i have isolation the reflector and check the MCPCB . Its ok. From where should i check the continuity? To MCPCB.
Best regards Thomas
HI no i understand 
i have check the continuity. There are not any continuity from Minus to the top of the MCPCB. ( the insulation side of the MCPCB)
Check both the plus to bottom of mcpcb and minus to bottom of mcpcb.
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I have continuity from minus to bottom to the mcpcb. But not from plus to the bottom to the mcpcb. Can it bee the soldering of the dioder to mcpcb?
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Yes!
You’ll need to reflow the LEDs
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Thank you so much for your help. You are great 
Best regards Thomas
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I was pretty sure this was your issue, because it’s happened to me!
Now I check continuity between + & MCPCB and - & MCPCB every time I reflow!
This sorta thing seems to happen more frequently with SFTs than any other LED for me.
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Now i have reflow the led. I used a heat gun.it was not easy. I get continuity most all the time. I tap on the led to get rid of excess solder , but almost it remain under the leds. I was about to give up, but a did not :-). so now the sofirn c8 works fine. It throws very fare comparision with the original Led. Thanks for all yours time an help i get Best regards Thomas.
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HI It works fine in 5 minutes, then it started flickers. Ihave clean all concact points, and screw on the retainer ring, But it didnt helps. best regards Thomas
Hi again. I can not turn of the light with the front switch, and it flickers on lower mode. can it bee the led again? continuity.? best regards Thomas
If all you changed are the leds then I would suspect that is the issue. Did a lot of solder come out from under the leds when you pushed down on them while reflowing? Perhaps you used too much solder still.
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It didnt came out any solder then i push down the led. It usely do that when i solder diffrent led , but not this time.
I’m running out of ideas. In your first post you said you still have the original MCPCB. You could try reinstalling that and testing whether these new issues persist. If they do not, then you know you likely have an issue with the reflow. If they do persist, then your issue may not be with the reflow.
You could also try posting a picture of the new MCPCB as it is installed in the light. Maybe we will see something for you to investigate.
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i Bought a couple of new MCPCB 3535 from sofirn. and modding couple of sofirn c8F with diffrent leds. , Osram KW CSLNM1 Osram KW CSLPM and Luminus SST-20. And never had this issue. The flashlight has stop flickering now But i can not turn it off with the front switch. best regards Thomas
But i can not turn it off with the front switch. best regards Thomas
Just a guess, but maybe it’s not one of the LED’s that is making a short to the DTP (or underside) of the MCPCB, but there is a cut in the driver wire on the underside, where it goes through the hole in the MCPCB and it’s making (sometimes) contact with the sides of the hole (and therefore the underside of the MCPCB).
First of all:
Measure again for continuity from the + and - on the MCPCB to the underside.
If there is continuity, desolder and remove(!) the wires and test again from the + and - to the underside of the MCPCB.
If there is no continuity anymore, than most likely the wires from the driver are the problem. Check the “underside” of the wire, where they are bend to be able to solder to the pads on the MCPCB. Look carefully for (really) small cuts in the insulation of the wire, because when they are deep enough they might just expose the inner wire enough to short to the underside of the MCPCB.
If one of the wires does have a (small) cut, then it might also explain why the problem is not consistent, because it could be that by tightening the bezel or even the driver retaining ring, there might be just be enough tiny movement of the wire to make or break the contact.
If you don’t have continuity at ‘step one’ (the “first of all” I mentioned above), it might be worth it to move the MCPCB around a bit to see if that changes anything or desolder the wires anyway and inspect them for cuts, just to be sure.
I already had it happen to me once, that the sharp edge of the MCPCB where the wire came through, made a cut in the wire (on the underside, so initially not visible) and made a short.
By the way: on your photo in the above, it does look like that the hole where the + wire goes through, has some damage to the white solder mask on the top and right side, maybe even going underneath the (red) wire. If there is a tiny cut in the wire, that might make just enough difference for it to make a short, while when you try a different MCPCB, which doesn’t have that slight damage to the white solder mask, not has a short. It’s just a theory, but there is a slight chance that it just makes that tiny difference.
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Hi again. I have continuity with the wires on. Minus to Mcpcb. i cant see anything wrong on the minus wire. i am going too remove the minus wire and check if it still have continuity. Thank you so much for your help. best regards Thomas
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If you still have continuity when you have desoldered the black wire, could you try to make a really detailed close-up photo from the - soldering pad?
On your current photo it is a bit difficult to determine, but the area around the - solder connection seems to be a bit dirty from some burned flux (I guess), while around the + soldering it is really clean. If it’s not ‘dirty’, but some slight damage of the white soldering mask (I don’t if you’ve have used ‘soldering wick’ to remove old solder?), there could maybe be some damage underneath the - pad or the trace, which maybe went through the insulating layer underneath the - path, that seperates it from the main copper mass on the bottom, and maybe therefore causes continuity.
I have to admit that it is very unlikely though.
The only other option I could think of is removing one LED at a time (and testing afterwards eacht time), to see which one might be causing the ‘short’ to the DTP.
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