Romisen RC-F4 Dimming Problem

frankiej · Mar 1, 2008

I recently received a Romisen RC-F4 from DX. When i first fire it up, it emits a intense, bright beam. After about 5-6 seconds, it dims down to about 50% of its original output. If i immediately fire it back up, it comes on at about 50% brightness, but if i leave it off for a few minutes, it will come on at full brightness, then dim after 5-6 seconds. It's like something is getting hot and has to cool down before it goes back to full brightness.

I've tried several different brands of batteries, and it still does this. Is there anything that i can check on it to fix this problem before I start with the hassle of sending it back? I thank everyone in advance for the replies.

meuge · Mar 1, 2008

frankiej said:
I recently received a Romisen RC-F4 from DX. When i first fire it up, it emits a intense, bright beam. After about 5-6 seconds, it dims down to about 50% of its original output. If i immediately fire it back up, it comes on at about 50% brightness, but if i leave it off for a few minutes, it will come on at full brightness, then dim after 5-6 seconds. It's like something is getting hot and has to cool down before it goes back to full brightness.

I've tried several different brands of batteries, and it still does this. Is there anything that i can check on it to fix this problem before I start with the hassle of sending it back? I thank everyone in advance for the replies.

It sounds like you're having heat problems. Try to take the pill out and make sure the star hasn't come off the heatsink, and is glued well... and see if there isn't a gap between the emitter and the star.

Does it turn bluer too?

Vikas Sontakke · Mar 1, 2008

frankiej said:
I recently received a Romisen RC-F4 from DX. When i first fire it up, it emits a intense, bright beam. After about 5-6 seconds, it dims down to about 50% of its original output. If i immediately fire it back up, it comes on at about 50% brightness, but if i leave it off for a few minutes, it will come on at full brightness, then dim after 5-6 seconds. It's like something is getting hot and has to cool down before it goes back to full brightness.

I've tried several different brands of batteries, and it still does this. Is there anything that i can check on it to fix this problem before I start with the hassle of sending it back? I thank everyone in advance for the replies.

First try to short the battery tube to the battery negative i.e. take the switch out of the equation. If it stays at the original output, then you know that the switch is the culprit. Mine had similar problem and I fixed it yesterday. It was not doing that before but started this behaviour or my newly acquired 17670 battery.

- Vikas

frankiej · Mar 1, 2008

meuge said:
It sounds like you're having heat problems. Try to take the pill out and make sure the star hasn't come off the heatsink, and is glued well... and see if there isn't a gap between the emitter and the star.

Does it turn bluer too?

I'll try this. I haven't checked that area. The light won't even come on full brightness now, so maybe something is already fried in there. I think it does possibly turn a bit bluer when it dims, btw.

Vikas Sontakke said:
First try to short the battery tube to the battery negative i.e. take the switch out of the equation. If it stays at the original output, then you know that the switch is the culprit. Mine had similar problem and I fixed it yesterday. It was not doing that before but started this behaviour or my newly acquired 17670 battery.

- Vikas

I tried this suggestion. It does not affect the brightness of the light when I short out the switch, so I guess that would eliminate that area as a problem.

Thanks to you both for your suggestions of what to check. I really appreciate the help.

frankiej · Mar 3, 2008

Well, just an update: the light doesn't even get to full brightness now. Apparently something fried in there. It is always about half of the original brightness now. I checked that the LED board is glued down, and it seems okay, and the switch isn't the problem.

It sounds like returning things to DX is a PITA, so I'm thinking about trying to fix it myself. Given my original description of the problem, do you think that the LED is bad? I'm assuming that there is some kind of circuitry inside of the little module that the LED is mounted to:could something in there be bad?

I'm thinking of ordering one of the 16mm Cree Q5 emitters from DX. I'd just pop the old one off, glue the new one in with some heat conducting epoxy, then solder it in place, correct? Sorry about all the stupid questions, but I'm a noob to flashlight modding. Is there some kind of "flashlight modding for dummies" tutorial on here somewhere?

Thanks again for all the help.

meuge · Mar 3, 2008

frankiej said:
Well, just an update: the light doesn't even get to full brightness now. Apparently something fried in there. It is always about half of the original brightness now. I checked that the LED board is glued down, and it seems okay, and the switch isn't the problem.

It sounds like returning things to DX is a PIA, so I'm thinking about trying to fix it myself. Given my original description of the problem, do you think that the LED is bad? I'm assuming that there is some kind of circuitry inside of the little module that the LED is mounted to:could something in there be bad?

I'm thinking of ordering one of the 16mm Cree Q5 emitters from DX. I'd just pop the old one off, glue the new one in with some heat conducting epoxy, then solder it in place, correct? Sorry about all the stupid questions, but I'm a noob to flashlight modding. Is there some kind of "flashlight modding for dummies" tutorial on here somewhere?

Thanks again for all the help.

It would work... but only if the problem is the LED, and not the circuit board. Unfortunately, in my RC-F4, the pill is glued into the body, so while swapping the LED is possible (just a little awkward), swapping the driver module is not possible, unless the pill can be unpotted.

frankiej · Mar 3, 2008

I took the pill out of mine, so it's not glued in place. No problem there. Is there any way to tell if the problem is in the LED or the driver, other than trial and error? If the problem was in the driver, could I order a new one from DX? I looked at the ones listed on their website, and i became confused as to which one matches it. Thanks again so much for dealing with my uneducated questioning.

meuge · Mar 3, 2008

frankiej said:
I took the pill out of mine, so it's not glued in place. No problem there. Is there any way to tell if the problem is in the LED or the driver, other than trial and error? If the problem was in the driver, could I order a new one from DX? I looked at the ones listed on their website, and i became confused as to which one matches it. Thanks again so much for dealing with my uneducated questioning.

If you have a CR123 or RCR123 battery, you should be able to directly drive the LED (just use a 1ohm resistor not to overload it).

The circuit would be:
+ terminal battery -> 1 ohm resistor (rated 5W+) -> + terminal LED -> - terminal LED -> - terminal battery

I am not sure if 3V would light the LED, so it would be better if you had an RCR123 to do this test.

You can just do this circuit using the surface contacts of the emitter... and it'll tell you whether the problem is the emitter or the driver.

Vikas Sontakke · Mar 4, 2008

I have noticed that there are many failures of F4 being reported. Is it just because *lots* F4 have been sold and percentage wise the reported failures are still on the low end as compared to others lights?

My F4 failure is on the "good" side; it has made it even brighter than the stock F4; nevertheless it should still be counted as a failure.

- Vikas

frankiej · Mar 4, 2008

Yeah, I'm kind of wondering about this model myself. I bought it because I previously purchased two of the Romisen RC-G2's. They turned out to be awesome lights. The RC-F4, not so much. Guess you get what you pay for, I suppose. It was an awesome light when it was at full brightness, all 6 seconds of it!

As an update, I've decided to try to give DX a chance to make it right (I also was missing the Romisen RC-I3 that was supposed to be in my order). I'm okay at soldering, but it looks like tight quarters in there, and I'm afraid I might fry something. I think it's ridiculous that you have to give DX pictures before you can start the refund process.

RecycledElectron · Mar 4, 2008

I've ordered and received 12 RC-F4's and only had one problem. One of my black RC-F4's was missing the clear plastic washer under the reflector, and the flashlight wouldn't work. I made a plastic washer and the light fired right up.

Maybe I've been lucky, I've had mine for over 3 months or more, so these are older manufacture.

I know that there have been some structural changes (perhaps depending on what vendor supplied the parts) and there are differences between the gray and black lights.

Alan · Mar 5, 2008

RecycledElectron said:
I've ordered and received 12 RC-F4's and only had one problem. One of my black RC-F4's was missing the clear plastic washer under the reflector, and the flashlight wouldn't work. I made a plastic washer and the light fired right up.

This is 8.3% DOA rate!!! I wonder how Romisen could still be running

Alan

Vikas Sontakke · Mar 5, 2008

Because I suspect UltraFire has even worse rate than that.

Romisen RC-F4 Dimming Problem

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