Beginner needs a little push: Coil/Inductor repair on LED pocket light board

[aBavarian Normie-Pleb]

Hi,

I would like to do a repair on a LED pocket light, though I'm an absolute beginner.

Observations:

- Issue: All red LEDs died at once.
- Disassembled the device and inspected the light panel, on one side there's the WWRGB matrix, on the other side there's a controller board.
- Coil with 330 written on it looks a little suspect (not as nicely aligned as other components).
- When powering the light on and applying a bit of pressure on that coil the red LEDs turn on until you remove the pressure.

I hope these details and the attached photos create a good enough basis for help.

During the pandemic I picked up some soldering equipment (regular iron, hot-air station, flux, wick) but life had some detours and I never got around to seriously train with the eqipment.

1) How easy is it to remove and replace such a coil?

2) Would resoldering it be sufficient or should I get new components?

Thanks for your assistance!

[inse]

Servus,
the coil has maybe ripped off the PCB by mechanical shock.
Simply try resoldering it with a decent sized solder tip of at least half the size of the pad width.
Having two soldering irons would be perfect to align the component conveniently.

[Ian.M]

If you zoom in on the '330' inductor in the second photo (view-a), it looks like the lead facing you has been ripped off the inductor body.  If that's the case, resoldering it wont help.  However, do try, but I suspect the lead in question will come away with minimal pressure when you reheat its joint to the pad.   I doubt there's enough exposed metal where the lead has broken to solder it back on successfully, but you might get lucky gluing the inductor in place and soldering a fine wire jumper between where the lead's broken off and the pad it originally went to.   If not, you need to carefully remove the inductor (so you can attempt to measure its critical parameters) and identify a suitable replacement, which will need to have a similar DC resistance and the same or greater saturation current.

[aBavarian Normie-Pleb]

Thank you guys for the responses!

Would it be bad to add a little flux on the inductor with the broken leg to remove any oxide layer and afterwards add some tin to bridge the gap?

Have also emailed the light's manufacturer, maybe they are kind enough and actually respond with "This exact inductor/coil is part xyz with these specifications".

[Ian.M]

It depends on how much of the broken off leg is left sticking out of the body. 'Tin' (by which I assume you mean solder, which in the case of ROHS Pb-free alloys is only a few percent away from being pure tin) doesn't bridge gaps well.  If there's enough to overlap the full width of the lead with the broken off piece and you bend it in a bit, your idea should work.  If its more or less flush, your only chance is to glue the inductor down like I suggested then use a U on its side shaped fine wire jumper, diameter the same or smaller than the lead thickness, between the lead remnant and the pad.  The broken off lead is too stiff and will just rip off again if the board flexes or is subject to impact.  The fine wire U jumper will be thin enough to flex so it doesn't rip off again.

[aBavarian Normie-Pleb]

I think don't have a certain image in my head how this kind of inductor/coil is constructed inside its little plastic housing.

- The housing has a footprint of about 6.8 mm x 6.8 mm, the distance between the contact pads on the PCB is 7 mm.

Does this hint at a certain type that has a nice schematic view of it available to help one's imagination?

[pcprogrammer]

I think don't have a certain image in my head how this kind of inductor/coil is constructed inside its little plastic housing.

An inductor like this probably has a ferromagnetic housing and not plastic, but I can be wrong.

If you have a multi meter you can check if it is still connected. With the meter set to Ohms it will report a low value if so.

When needed de-solder it from the board and take a look at the bottom side of it. You might be able to take it apart and bring out the wire of the coil.

The photo does not show it, but it can also be that it consist of two halves stuck together.

Edit: the fact that it works with pressure applied shows there is a break in the circuit, but the question is if it is outside or inside the coil. When the break is outside the coil the trick with a small wire Ian.M mentioned might fix it. Otherwise you have to open it if possible and get it back together again without changing the specifications due to a larger gap between the ferromagnetics.

[aBavarian Normie-Pleb]

[...]

Have also emailed the light's manufacturer, maybe they are kind enough and actually respond with "This exact inductor/coil is part xyz with these specifications".

The manufacturer responded:

Inductor with 330 written on it: 0605-330M (7 x 7 x 5 mm)

Can anyone recommend a retailer in Germany or the EU, am a bit worried about subpar/faked parts (while I don't have maker experience yet I know of the news about quality issues especially since the last pandemic).

[fzabkar]

https://de.rs-online.com/web/
https://de.farnell.com/
https://www.mouser.de/
https://www.digikey.de/

[aBavarian Normie-Pleb]

None of them finds a result for that part number...?

[fzabkar]

It's more of a description than a part number. You need to search for a 330uH coil/choke/inductor with those same dimensions.

[pcprogrammer]

https://world.taobao.com/item/623552840213.htm

Not sure how to buy there, but this does look like what is on your board.

[Zoli]

It's more of a description than a part number. You need to search for a 330uH coil/choke/inductor with those same dimensions.

33µH, not 330µH(33*10⁰=33)

[mariush]

Maybe it's Coilmaster SEP0605 series : https://www.coilmaster.com.tw/es/product/file/655734-1

There's a SEP0605E-330M-LF  and the size is close enough for them to round it ... 7.3 x 6.6 x 5

The specs would be 3.5A Isat saturation current , 2A for Irms and <200 mOhm DCR ... so you could buy any inductor that's has better specs than this (bigger Isat, lower DCR) and similar footprint.

This would seem compatible : https://www.digikey.com/en/products/detail/w%C3%BCrth-elektronik/74437349330/2791025

i think same part is here on farnell : https://de.farnell.com/wurth-elektronik/74437349330/induktivit-t-33uh-3-5a-we-lhmi/dp/2077813?st=33uh

a potential alternative ... around 7.9mm x 6.7mm 4a saturation current : https://de.farnell.com/kemet/mplcv0654l330/induktivit-t-geschirmt-33uh-20/dp/2840083?st=33uh


this one is less than ideal at 3.2A saturation current, and 8x8 mm but you'd be able to solder it and would probably be fine : https://de.farnell.com/vishay/ihlp3232dzer330m11/inductor-power-33uh-3-2a-20/dp/2545034?st=33uh

[aBavarian Normie-Pleb]

It's more of a description than a part number. You need to search for a 330uH coil/choke/inductor with those same dimensions.

Hopefully not another ignorant question: If I understand it correctly the only electrical specification that the manufacturer gave me is the 33 µH. Should I inquire about the other details to be on the safe side or am I overthinking things here as a lay person?

Also: Could I improve the efficiency of the pocket light by replacing the inductors with "higher qualiy ones"? Or is the loss here marginal compared to the LED matrix as a whole? The entire unit's light output is around 18 W.

[mariush]

It's 33uH 

If the component is small, manufacturers generally use the short notation, where the last digit represents the number of 0s after the value.
So the 330 printed on the inductor actually means  33 x 10⁰ = 33 x 1 = 33 uH.

For decimals, you would see R used, just like on resistors... for example you have 3R3 on an inductor, that means it's a 3.3 uH inductor.

No, changing the inductor to a bigger value will not change the efficiency significantly.

Ideally, you would determine what LED driver IC  is used and you'd get the datasheet for that LED driver IC, and if you're lucky the datasheet may have explanations about how the inductor value and other parameters of the inductors should be chosen.  The chip is that 8 pin SOIC chip between the AP20N06 mosfet and the inductor  (each driver is accompanies by the mosfet which is basically an on/off switch to send pulses of electricity into the leds or inductor, and the inductor) - try reading the text on the chips ... if it's hard to read, maybe wet your finger and drag it over the chip, sometimes it helps make the text more visible.

Usually you optimize the inductor value based on how much power you give to the leds and how high or low the voltage going to the leds will be.  You would also optimize the value based on the switching frequency of the led driver ... but that's often fixed or hard to change, and it's chosen to be high enough to not cause visible flicker when you record something under such lights.

[inse]

Why not make a long story short?
Resolder the coil, if you doubt the stability, fix it with epoxy glue and you‘re good to go.
No need to make a science of it.

[aBavarian Normie-Pleb]

Made an old-fashioned scan of the board, maybe the eagle-eyed users among you can see more details here (please excuse the file size).

The reason I hesitate and don't "just do it" is that I want to be absolutely sure to be able to source the best-suited spare part if I mess up.

Is there anything obvious "not that great" PCB-design wise with that light controller board regarding its intended use case (regulary warming up/cooling down)? I'm asking since I'm about to buy more of them since they have been the only ones I'm happy with so far regarding the light properties (sensitive eyes), especially when using colored light and hope to use them for many years.