Light keeps cutting out

I know that there is a simple stupid answer to this that I just can't seem to find.

I grabbed a TF 502-B from DX back in March that was flaky as hell from day one. (shocking, I know) Light kept cutting out, had to jiggle switch, smack it, etc. Got a replacement. Same thing. (Still shocked) Got a partial refund to try and repair it. Tried re-soldering all the switch connections Picked up a "normal" hi-mid-low drop in for it from Manafont. Seemed to work, but then back to the same thing. Replaced the switch. (which was a joy cuz none of the replacements that I got fit, so I had to retro fit it to the board that was on the OEM switch) Seemed to work for a few days, then back to the same. Pulled it all apart, cleaned the threads, contact points, etc. Again, good for a few days then back to smacking it every few seconds to get it to work.

What am I missing here? Noalox at the contact points for the drop-in? The working for a few days then stopping has me thinking that it's just oxidizing and losing ground.

Have tried multiple batteries in it with the same results. Everything from the old blue TFs to CGR18650Ds to AW IMRs to Callie's. Always good for a bit, they starts cutting out.

If I pull it all apart and re-tighten it starts all over again. Good for a day or so, then starts getting worse. If I smack it against something (generally use it when walking the dog and tap it against the retractable leash) it's good for a few then cuts out again. Actually it doesn't cut completely out, but gets so faint that you can just barely see it.

It is driving me nuts because I can't for the life of me figure out what is losing connection. My gut is telling me it's the ground (well, my gut and the tapping ), but I can't see any problems anywhere.

I think that you may have nailed it about the pill and board not being properly attached. Would explain why many of the times it cuts out is when I am switching modes...the momentary puts pressure on it and then lets it back off allowing the break/bad contact.

Guess there's no harm in pulling apart the drop-in (with the "such useful strobe modes") that I will most likely not use...well unless I grab a host cheap somewhere.

Back of light to front: Loose nut or ring on clicky. Poor solder joint on spring. Spring needs to be stretched a little. Dirty spring contact. Dirty end of light where tailcap screws on.

Loose pill/dropin. Dirty spring. Poor/no/broken solder joints on spring and/or pill-to-ground contact. Poor solder joints on driver board, or lousy wire to LED.

Battery too short-stretch springs in light if tension poor. Clean both ends of battery with Deoxit or pencil eraser. Battery itself has intermittent somehow.

Keep us posted!