BLF17DD Troubleshooting

So you get this result on the bench as I read your post.

This is just an idea.

Maybe try to test for continuity from various points on the driver to where there should be none. Sounds to me like you may have a leak current somewhere. Operative word: may

Obvious ones are:

from spring to negative ring

From negative led pad to negative ring

From gate to negative ring

But sooner or later someone has to get a dud. Sorry if it turns out it is you.

Thanks for the tips led… I put power direct to the gate though- it should have opened and didn’t. I’ve even tried with a brand new driver and ic clips to the fet. Same results. It’s just a dud :frowning: They’re cheap though only a buck each on mountain- already ordered. Picked up some efest batteries too, fry me another chicken.

But really I haven’t had a problem with that buck on the yezl. I braid the diode to the pill wall and it handles 6 amps with 2 batteries in series without breaking a sweat. One’s being used nightly by my redneck kin. I’ll fix this but I’m not too confident it will hold up. Be nice to compare the efest to the mkne. I have a feeling it’ll be the same though. Oh well :slight_smile: Live and learn.

So it did not open at all?? Then I did not read that post right. Sorry for the confusion then.

Yeah thanks for the tips though. Not sure what happened really if it’s uncommon.

I think RMM gave me a dud! j/k I’ll update when it comes in. Why I outta! *shakes fist

Fellfromtree mentioned this thread & problem over in the BLF17DD Info Thread - Reference (post #142) and I thought I’d chime in. Fellfromtree mentioned a suspicion that the gate drive resistor might be incorrectly spec’ed, but I don’t think that should be the problem. AFAIK the gate drive resistor is simply there to protect the MCU from a potentially heavy drain on it’s little 20mA-per-pin sourcing ability - NOT to protect the FET from anything at all. Besides just getting a bad FET, I think the most likely thing sounds like a sudden open circuit during operation.

Offhand I’m not sure if turning off the tail clicky should be able to cause a voltage spike, but disconnecting the LED definitely should be able to do that. (Due to the inductance in the wires to the LED.) Here it sounds like the LED was already securely wired in, so I suppose that we can assume the LED was not suddenly disconnected it. In that case I guess the tail clicky did it? Hmm.

BTW fellfromtree… you have confirmed that the LED is OK, right? EG at some point after this incident occurred you wired this LED up such that you saw that it is capable of lighting up at the normal maximum which you are accustomed to?

Yeah it’s good. I even took it all apart and used another led.

So a disconnect from the LED could cause the FET to go? That’s interesting stuff. I dunno what happened- I’ll replace it though and hopefully doesn’t happen again :slight_smile: It doesn’t light up to the normal through the FET, the gate is just stuck

Thanks Wight… I’ll double check all my connects to the LED next time. I didn’t know a disconnect could cause something like that

I’m pretty sure it’s possible, but I wouldn’t really expect it to happen under normal circumstances either. More of a hypothetical problem. Long heavy gauge wires would probably make it more likely to happen, maybe especially if they were looped around a certain way (like an inductor).

If the FET is running cool then current flow isn’t bothering it. So while the FET is running cool the only potential problem is voltage spikes, and voltage spikes come from the inductive stuff going on in your wiring as the FET switches on and off.

I feel like you’ve probably hit the nail on the head when you say that you might have gotten a bum FET.

In bench testing I've done all kinds of unapproved stuff like that - holding the emitter leads to the driver pads instead of soldering, just to get a quick reading on something, fingers slip, wires come loose, etc. If there's a wrong way to do it, I've done it, but no dead FETs.

Fair enough. My own behavior along those lines is what I was thinking of when I typed #11. I haven’t done a fraction of the fooling around with FET drivers that you have, but I’m sure that if suddenly disconnecting the LED normally killed FETs we’d know by now.

So, that said… what’s your theory on what did kill the FET? Fellfromtree has done the requested checks as far as I can see and the FET sounds like it is in fact dead…

When there's no rational explanation, blame it on ESD. :D

Even though ESD happens with robust parts like this about as often as a rogue cosmic ray strike, you get taken seriously if you blame ESD.

I have a 12*7135 (I stacked 4 chips) on a Convoy S2+ build I did, it ran fine for a while but now it won’t come on but in moonlight (lowest) mode for some reason

I wonder if possibly the diode feeding voltage and for reverse polarity is bad…I will have to check

I had that happen and it turned out to be a flux corrosion issue on one of the inputs to the XM-L emitter. Same deal, just a low moonlight output. Driver was fine, and the emitter was fine once removed from the MCPCB.

It’s a 3x XP-G…ran great for about 5 min testing it out, shut it down…won’t come back on, I used a prototype ramping from turbo down to high (1 tick ever .25s) vs the large step down…I think it’s the firmware…but will re-flash just to make sure

But I will definitely check the inputs just to make sure…thanks!

Well, worth remembering that ESD adds up slowly over time, it’s not like being struck by lightning.
They used to call it “wounding” in the old days. A semiconductor has a narrow range within which it changes from being an insulator to a conductor — and ESD can change either side of that range by some small amount. Once enough components have wandered slightly off spec in various ways, the sum total performance of the circuit is, I believe the technical term used to be ‘cattywampus’

But maybe things like that don’t happen any more. I recall they never happened to young people, only to older people ….

Just fixed it reflowed with a heat gun and tested- looks good

Good to know hank, I havent wore a ground strap in years, maybe that would be a good idea :bigsmile:

You fixed it by reflowing the existing FET or by reflowing to swap on a new FET?

Doh you know I gotta start checking subs… It was actually quite a crazy ride on this one. I took off the old FET with a heatgun, put on the new FET. But then I was tired and hooked up the positive and negative backwards on the bench xd The diode was bypassed because I was testing what mods I could make to the board- so I had a wire going B+ to the cap, bypassing the diode.

I wanted to see if I needed the cap or not, as I don’t monitor that or write to memory on the Tiny13a- trying to optimize it for future builds xd If you will… Anyways The whole top end of the board started smoking. So I replaced the Tiny13a (checked out dead) and put in another FET as it wouldn’t fire up anymore. The stuff on the bottom all checked out. Then this is funny. I’m tired and solder fumes are giving me a headache. I clipped the led on, causing a short and shorting out the path. Turned it on to test- fried the diode (which I had just bypassed a minute ago).

Ok now I’m running out of parts. I put in a new diode and replaced the FET again just in case- it took a lot of juice through it with that short. Now my wife comes in and is like- what chu doing willis… Well Fing up

So I learned a lot that night, I really didn’t lose out. I learned what blows in reverse polarity. I learned what blows on a short. So now I have a deep understanding on what not to do and hopefully wearing a mask will let me undo the rosin flux damage to my brain

Hmm.

  • Can you use pastebin or whatever you want to share the code you’re using which you think does not write to the flash?
  • The C1 cap is always required, it’s called a decoupling capacitor or bypass capacitor - it has nothing to do with memory or the flash. The offtime cap is only required for offtime firmwares, not ontime or momentary. (I do not know if the offtime cap is used for dual-switch firmwares.)
  • You fried the diode while it was bypassed?
  • …or you unbypassed the diode and then fried it? Frying the diode with a dead-short from LED+ to LED- shouldn’t be possible I think.
  • Rather than a mask for those fumes, ventilation is the normal solution. Also called fume extraction. soldering ventilation - Google Search
  • Good thing these parts are cheap, right? :wink: :stuck_out_tongue:

It’s all working now. Only fried the diode after I took out the bypass… Which is funny cause I had it bypassed a minute before clipping the leads to the led without a isolator put on the bottom of the noctigon xd

Yeah reverse fried the mcu with the bypass… Glad parts are cheap, and I learned a lot in the mess. Basically stupid stuff- I’m usually careful but get careless when I’m tired…

Thanks for the link on that cap wight :)… Was wondering if I could get rid of it. The code I used STAR Firmware by JonnyC - Source Code and Explanation

EDIT I see it the OTC would be under Star 3 OSH Park ~

  • I still really have no idea what you are trying to describe. I’d like to understand how the diode got fried and nothing you’ve mentioned so far actually says what you did in order to fry it. :~
  • I know (and hate) the feeling of making those stupid, careless mistakes while tired. You’d think we’d learn to avoid it! For my part I probably continue to venture into that territory because I’m stubborn.
  • Ah, that’s right you did post it there! A momentary flashlight is really the only way you can have more than a single mode and refrain from writing to the flash.