by the way- I have no idea why my posts show different fonts!
q1 is my prime suspect.check between the group of 3 leads and the group of 4.
the one by itself is the gate.
most likely the resistor mod did it in as it was already on the edge.
post part number.you need a higher current/lower rdson rated part if you want to push it.
Thanks Snakebite, Keep in mind that I am in over my head here, so would you please keep suggestions geared towards idiots like me? What is, and how would I test Q1? I have ran this light for months since the resistor mod, without problems. This time it was in my bag, covered with clothes, so the massive heat build-up must have done it in.
Q1 is a mosfet.
post the numbers on it.
see if you read a short/low resistance between source and drain.
gate is the pin by itself
Ok checked Q1 and it shows continuity (1 probe on the 4 pin side and 1 probe on the single pin on the other side). Part number is as follows;
S426
AN
T28M
This is the order that they are listed on the mosfet. Should also note that there are some strange symbols on both sides of the center AN letters. 1 looks like a delta sign.
Should there be continuity across this component? Did I check the right pins?
One other thing that should be noted, I hooked 8.34v directly to the positive and negative wires running to the LED’s and all three emitters lit.
Is it this:
Hey Jim, That was fast! That may be it. I just scanned that whole document, and the only thing I understood was the sentence that stated this component should no be soldered with an iron…lol. Hopefully someone with the right expertise will chime in here.
If it’s a MOSFET as snakebite indicated, and if it’s the part in that PDF, then it’s probably used as a power switch.
If you look at the small drawing on the upper-right of the PDF 1st page, there’re functionally 3 pins:
(S)ource
(D)rain
(G)ate
i think the gate pin is the control pin. If that’s the one, it has 8 pins, and several of them are tied together, I guess to have lower resistance and be able to carry more current.
But like you found when testing the capacitor, if some other part has the pads that go to the MOSFET shorted, measuring it while it's still soldered to the board will do no good. Also, since it's basically a relay, if something is commanding it to turn on at all times, that will also cause the short. In that case, the MOSFET would test perfectly fine off the board, and the short would be gone with the MOSFET removed, but reinstalling it again would cause the short to come right back. Also, on a multi-pin part like that, the only way to remove it without cutting the pins is with hot air. In your situation I don't think there's much sense in removing components until it's known which exact one is causing the problem.
For applying power from an unprotected cell, what I mean is to tap the wire onto the driver contacts for a small fraction of a second, then wait 1-2 seconds, then tap again, until the problem area makes itself known.
What is Q1, anyway? Reverse polarity protection? If it's truly sitting between B+ and GND, I can't think of anything else it could be. If that's what it is, and it turns out that's what is causing the short, just remove it and leave it off. You'll only lose the reverse polarity protection, and in a light with a carrier and cell layout like the TK-75, it would be rather difficult to hook it up backwards anyhow.
q1 drives the big inductor.
its a buck converter if leds are paralell boost if series.
its definately bad.
has to be removed/replaced with a hot air pen.the metal runs deep under the package and it uses the board trace as the heatsink.
i could do it with a soldering iron but its easier with the airpen.
with your lack of experience i dont recommend you try.
the datasheet seems to be the one.i can look for a better replacement.
if nobody local can help you i can swap it out if you mail it to me.
hopefully the gate driver is ok.they usually are.
Hi,
That is a very generous offer! This is why I love BLF :)!
...huh?
What do you mean by 'drives the inductor'?
Q1's four drain pins connect to the output (left) side of the inductor, with the BAT+ input to the inductor's right side. What does Q1's three source pins connect to? Ground? It connects the inductor's output to ground when triggered?
Ohaya, you’re right that is a generous offer. Just wanted to say thanks again to everyone that are the time to help me here!
yes.it feeds the inductor pulses which create higher voltage spikes during turn off.like an ignition coil.q1 is the”points”a solid state switch.
d1 rectifies them and c3 and the one above it in paralell filters the output.
a simple smps.
the low value resistor is a reference.thats how the regulation is done.the smps chip/micro monitors the drop across the resistor.
oh and DO NOT try the “smoke test” mentioned.
you may get to see a nice fireworks show if those yellow caps go.will make a big mess of the board.
If the problem is the one in the PDF above, it seems not hard to find in the U.S., e.g., Digikey:
digikey is the way to go.
can even do 1st class mail.
I know. Isn’t that amazing? That (the cost of shipping from them) used to be a big obstacle, but I’m finding that I’m buying more stuff from them nowadays, thanks to the USPS first class shipping. Plus, they ship super fast, and pack stuff like there’s no tomorrow:
The above was a package I received with ONLY two tiny cut-tape strips of resistors (pen is for size comparison)!