Troubleshooting Nitecore MH25S

Hi guys I have good and bad news

Good: I just received my brand new Nitecore MH25S

Bad: it’s misbehaving

Both in daily and tactical mode it doesn’t do anything when the back button is pressed. It only kinda works if I press both the back and then the mode button, then I can cicle trough the modes, but tactical mode is the worst, momentary illumination doesn’t work, half pressing should give momentary on but nothing happens, doing the same routine of fully pressing the back button and then the mode button it turns on in low mode but tactical should turn on in turbo or strobe.

What I tried and didn’t work:

Fully charging the battery

Checked the plate inside the tailcap but it wasn’t loose.

Tried changing between daily and tactical modes

I didn’t remove the head because from what I know it is glued, and I don’t want to disassemble it because I may have to use the warranty.

I have a MH12S and the tailcap is the same so I tried changing the tailcap and it didn’t work

Could anyone help ?

Dual-tube design, right? Edges might need to be cleaned.

Thank you Lightbringer for answering, could you help me understand that?
Sorry, I’m new to the forum, previously I didn’t do any maintenance on flashlights so I’m not familiar with the terms. Could you talk to me as a dumb newbie? What edge could be the problem and how should I clean it?
Also I’m not sure how to check if it is dual tube, do you mean there’s a double wall in the tube? Like an inner and outer tubes ? From the back without the tailcap the tube seems to have only one wall, I can’t find any visible dirt or debris. I’ll try to learn how to post pictures so I can send anything that could help.
Sorry to bother you

Clean the edge of both ends of the battery tube, the place where there’s no black anodizing. Could be a poor connection, if not that then I suggest sending it back

No bother. There might be a sleeve which fits inside the battery tube that carries the signals from the tailcap (vs the body itself which carries the main current).

They gotta be clean to give good contact on both ends.

Ain’t got the light, so am only guessing if it’s a dual-tube design.

What battery are you using?

I cleaned the back end of the tube with isopropyl alcohol, no effect, the front end of the tube is glued to the head so I don’t want to dismantle in case I need to send it back.

Thank you Funtastic

Thank you Lightbringer for explaining, I get it now, unfortunately cleaning didn’t help but it was a great tip

I’m using the battery it came with in the box Nitecore NL2150
Thanks for your help

I didn’t realize until now (because I don’t use it much) but the strobe, beacon and SOS modes don’t work.
According to the manual they should work by long pressing the mode button when the light is on.
Don’t now if it helps diagnosing the flaw but, I thought I should mention it.

Just goggled it, seems the mode button is on the side, not a 2-switch tailcap, so likely no dual-tube design.

Sounds like it might be the switch or the driver. Whenever a light goes mental, I always blame the driver, which is most likely, but no momentary points to the switch.

In short, no idea.

I’ve accumulated three of the newer “i” lights (have two older models too) and the only issue I’ve had was with the older model that’s been in my messenger bag for years that I had to clean the contacts off with. Maybe shine a light down into the tube and see if the contacts for the positive side has any smudges on them. You can dip a Q-tip (or something similar) in alcohol and try to clean it.

If you purchased this from a reputable seller, I might suggest contacting them seeing if you can get a replacement. Hopefully the shipping isn’t too much. Hopefully this is just a rare lemon and you can get up and running soon.

Thanks for all the effort Lightbringer

Hey Scotty, thank you for your input
I have looked inside, all looks clean but I tried using isopropyl alcohol with a cotton tip to clean it anyway, unfortunately no luck

I have bought a few Nitecores recently, P30i, MH12S, P20iX and this MH25S, only the MH25S had been giving me headaches so far
I believe it’s an isolated case
I’ve bought from Nitecore’s official AliExpress store, so I’m waiting for their response.

Thanks for all the help

My flashing blue battery indicator button quit woriking just the other day.

Hey guys thanks for all the help, just an update, I had bougth the MH25S from the Nitecore official store on AliExpress, they offered a partial refund, after some negotiation I bought a P20iX (I was going to buy anyway) and they agreed to send a working MH25S in the same parcel. When they arrive I’ll update this thread. :smiley:

Was it a MH25S?

Update: unfortunately Nitecore didn’t send the replacement with the new order, they said it was a mistake. I’m forced to open a dispute in AliExpress before the time to dispute runs out.
Very sad to see this happening as I’m a big fan of the brand

Hi Renato. It’s bad when that happens, but fortunately, you had bought it from AliExpress, so they will send a new light or your money back.
Glad to see another Brazilian guy here :slight_smile: