zebra H501 flickering

I have an h501 that is about a year old and flickers very slightly when on. It only seems to be noticeable in high mode and it often stops if I just tap the light a couple times. cleaning it doesn't make a difference. Any ideas?

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Try a different battery. If that doesn't work then I'd send it to ZL for repair.

I sometimes get flickering from one of my (many) ZLs. So far it has always been either a low battery or a poor contact somewhere (ie easily fixed). Did you clean the +ve contact up in the head end ? (I use a hard eraser on the end of a pencil for that one, it is a bit hard to get at)

+1 Gregozedobe's comment.

If you're getting flickering with a solid state device and the flickering changes when you tap it then the problem is probably in the non-solid state areas, namely the interface between the battery and the terminals or the interface between the shiny aluminum ring at the end of the flashlight body and the gold ring down in the tailcap.
-the only other non solid part should be the 200,000 cycle rated switch, which is an electric switch and shouldn't be any factor with flickering, it would either send a signal or fail to send a signal.

I have the same problem with my H501w. I have cleaned it with DeOxit, and also spray electrical contact cleaner. Nothing I do can completely eliminate the flickering on high. I have multiple Eneloops that are all new and properly maintained. I also have other rechargable LSD nimh around. For me at least, it is definitely not the batteries. I also tried resoldering the spring in the tailcap to see if that was the weak link. Nothing consistently works for me, so good luck to you!

wow. Mr. Tone, sounds like a thorough intervention.
Have you also tried a lithium battery with the same results? I don't understand all about the electronics involved, but I've been able to consistently see flickering with my AA zebralight when the battery is nearly depleted and I assume that it has something to do with voltage being stepped up to supply the led and the depleted battery not being able to keep up, and so the voltage stepping up in little pulses instead of a steady flow.
Maybe there is some critical variance in components that will let some of the lights pass QC while being unable to supply max power in some conditions, but it seems much more likely for it to be a moving part issue.

Can you replicate the problem with the tail cap off, bridging between the battery and the base with a penny or something?

I have not tried to completely take the tailcap out of the equation. I will have to try bridging it to see if it happens. I have had my Zebralight flicker even when the Eneloops are hot off the charger. They come off the charger between 1.45 and 1.5 volts. The voltage holds up well under load with the Eneloops as most of you know. I guess that it is either too much resistance somewhere in the electrical path or a problem with the regulation circuitry. It never flickers on medium or low modes, only high. FYI I have the older model before they had the moonlight mode. Mine has low, medium, high, and hidden strobe.