Help figuring out electronic part

Thread Starter

jaberz

Joined Oct 18, 2023
9
Hello, I have a subwoofer that stopped working, one of these two parts has failed, the big one I have found as there are markings on it, the little one I have no idea, can anyone help me identify it?
1000006294.jpg
 

bertus

Joined Apr 5, 2008
22,264
hello,

next to the part is written FB901.
the part could well be a ferrit bead.
when you measure the resistance, the value should be very low.

bertus
 

Thread Starter

jaberz

Joined Oct 18, 2023
9
hello,

next to the part is written FB901.
the part could well be a ferrit bead.
when you measure the resistance, the value should be very low.

bertus
Thanks a bunch Bertus, I already searched about the fb901 without any luck as I have no idea what kind of part this could be. If it's a ferrite bead, could this even be the part that failed and caused the short-circuit?
 

ZCochran98

Joined Jul 24, 2018
303
The 901 refers to a particular instance of that part (a label). For example, if you had several resistors they would be labeled R1, R2, R3, etc. Or, if the device has multiple boards, sometimes they're labeled with a board number and then a part. If the resistors in my example were on the same board, except the third one, then they might be labeled R101, R102, and, say, R305.

Without further info, you're not likely going to find an "exact" ferrite bead replacement. Depending on the application, ferrite beads tend to be used to block high-frequency signals or noise from passing through, so if you find a low-resistance ferrite bead, you might be able to use that.

Now, for your specific problem, it's possible the bead is damaged, but I would hazard a guess that the "big one" in your picture (most likely a MOSFET or similar) is probably what's gone bad.
 

MrChips

Joined Oct 2, 2009
30,488
Ferrite bead FB901 is exactly that, a piece of wire with a ferrite bead around it. It should measure 0-ohms. It is very unlikely that this has gone bad.
No, it did not cause a short circuit. It is supposed to be a short circuit at zero frequency.
 

Thread Starter

jaberz

Joined Oct 18, 2023
9
Thanks so much guys. I'm going to order and replace the "big one", and fingers crossed my woofer will work again.1000006296.jpg
 

Audioguru again

Joined Oct 21, 2019
6,610
When an electronic part has a short-circuit then it usually does not get hot, instead another shorted part causes this SARS10 diode to get over-heated.
 
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Tonyr1084

Joined Sep 24, 2015
7,777
I'm going to order and replace the "big one", and fingers crossed
Would recommend against that approach. Something blew this part out. Putting a new one in is like standing in front of a speeding freight train. It's going to get hit and likely destroyed. Looking at the board and adjacent jumper wire, there's been a tremendous amount of heat. A failed component fails and quickly cools. That part has suffered a duration of over current causing the part to burn the board. Before replacing anything fully diagnose the problem. Otherwise you're just spending your money to toss new parts in the trash.

A full diagnostics of the board needs to be done by someone who knows what they're looking at. All we can see is a few components, no circuitry, no schematic, no component values and no voltages. From where I sit - diagnosing the problem is not possible. Again, "From Where I Sit".
 
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Tonyr1084

Joined Sep 24, 2015
7,777
By the way: Those markings on the board are put there by the manufacturer. According to the Bill Of Materials (BOM) those components are identified as to what they are and their values. Without the BOM we can't know the values without being able to read them directly. FB901 simply is the component found on the BOM. The BOM will tell you specifics about it. And no - ferrite beads do not go bad. They can break, but they don't go bad. That's one component you don't need to replace. Not unless heat has caused it to crack.
 

Thread Starter

jaberz

Joined Oct 18, 2023
9
I'm in no way a specialist and don't know what I'm doing, hence this post. But I'm afraid that anywhere I would bring it to, they would just tell me to toss it in the trash even though I'm (hopefully) sure it is possible to repair..
 

MrChips

Joined Oct 2, 2009
30,488
Bonjour. You came here for guidance. That is a good start.
The first thing you need to do is to tell us the make of model of the subwoofer. There is always a chance that we can locate a circuit schematic. A circuit schematic is the electronics engineer's roadmap of what is going on and where we need to go to look for clues. Anything outside of that is just guesswork. We solve problems like this one by looking at functionality and purpose of components within the circuit.

As stated already, there is short on your board. What we need to do is locate that short, not just replace components at random.
 

Thread Starter

jaberz

Joined Oct 18, 2023
9
Here you go, thanks a lot already for the help. You'r too kind good sir. If you need some close up, ask away
1000006488.jpg1000006487.jpg
 

MrChips

Joined Oct 2, 2009
30,488
Disconnect the unit from AC power.
With an ohmmeter, measure the resistance across GND (pins 1-4) and VPDD (pind 6-8).
Reverse the ohmmeter leads and measure again.
 

MrChips

Joined Oct 2, 2009
30,488
Here is the SMPS schematics.
I am going to make a guess that the problem lies on the primary side of transformer T901.
Possible suspect is IC901 for starters. Bonne chance.

LG woofer SMPS circuit schematics.jpg
 
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