Blew MOSFET in amplifier, but don't know what to replace it with - Page 1
Forum section: electronics / repair

author: ErinBob
author_rank: Newbie
timestamp: February 24, 2024, 11:42:30 am
content: This car amp got fried and im hoping to fix it.. the amp is a 1 channel 1500w, model TSG-1100.1D, made by "TopStrongGear". anyone see anything i should check out closer?? I've still got the component, burnt though. It was labeled simply "B1". I can't even find any data on such a simple label...I know that often times in amps Mosfets and transistors are designed in pairs.. i know someone out there can figure it out,, but id like to learn how also!...or just give me the answer if its too toughSo there could be more wrong possibly...and I'm not even sure what it was... thanks for at least reading this far! The top row of components has 3 legged things labeled "B1" in the first 3 places. The forth, is the missing one and the 5th labeled "2312 S4". The last one is similarly labeled "2306 S3". Those two are labeled S4 and S3 on the PCB also though. The board is too scorched to read what it called the missing one.. can I just assume that it was the same as the first 3, and if so, how do i map/measure one of those?? The first 3 in the row are labeled Q10 Q11 and Q12 on PCB...all the ICs on here are simply labeled C or C3, or C8....

author: ErinBob
author_rank: Newbie
timestamp: February 24, 2024, 11:45:53 am
content: Some other shots...

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: February 24, 2024, 01:29:15 pm
content: Yes its the same as the other three, BUT B1, B2, B3, B4... are custom numbers used by cheep manufacturers usually in country starting with a B.....First, you can use the other parts to test and spec a replacement part with the proper tools and equipment.Second, you can guess and try subs for the part/s (depending on amp design) you may have to replace the oposite side also, all with matched parts.A picture of the whole amp might help if someone has run into this before and found replacement parts as these are sold under many names.Jeff

author: ErinBob
author_rank: Newbie
timestamp: February 25, 2024, 08:54:38 am
content: Here are more pictures if this helps

author: ErinBob
author_rank: Newbie
timestamp: February 25, 2024, 08:55:38 am
content: And more

author: ErinBob
author_rank: Newbie
timestamp: February 25, 2024, 08:59:39 am
content: ....and more. So after removing one of the others labeled the same, how exactly do I test for finding a replacement? Do I need a oscilloscope or a cathode ray component tester....I know I can get it if it involves enough tequila and soldier!Thanks again

author: DavidAlfa
author_rank: Super Contributor
timestamp: February 25, 2024, 09:10:48 am
content: They have been relabeled.... Search "MOSFET 60v" in AliExpress, anything capable of driving >50A will probably do the job here.The IRFB3206 is capable of 210A continuous.

author: markusdd
author_rank: Contributor
timestamp: February 25, 2024, 01:29:47 pm
content: agree with this take.it's probably not worth it to even try to replace these relabeled 'junkers' (they even could be some hidden quality type FET, but certainly not top of the range).Just get a set of e.g. the suggested IRFB3206 and be done with it.

author: ErinBob
author_rank: Newbie
timestamp: February 25, 2024, 10:36:16 pm
content: Thanks, I will just do as you say and replace them, do you think in a circuit like this there are any other parts "coupled" to these ones that I ought to replace while I'm at it? I might just use the IRFB3206 you mentioned to eliminate that being a risk anymore. Thanks again!

author: markusdd
author_rank: Contributor
timestamp: February 25, 2024, 11:29:26 pm
content: I wouldn't suspect there is a need for anything else right now, I mean the failure mode is pretty clear, that FET blew out its gutsThe recommended FET is not of any 'special' nature, it just ideally 'just work' in this scenario.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: February 25, 2024, 11:44:15 pm
content: Quote from: markusdd on February 25, 2024, 11:29:26 pmI wouldn't buy it from Ali Express though, they will more likely be similar to the original that blew up.

author: markusdd
author_rank: Contributor
timestamp: February 26, 2024, 12:01:51 am
content: absolutely true. Aliexpress is hit and miss.I got lucky though. Wanted to replenish my random parts pile a bit and got some 'universal' replacement components and e.g. the IRLZ44N that I got ar egenuine International Rectifdier ones, also the measured values all check out.The reviews often actually can help. I went through the practice of actually saving the stores that I had good experience with in my account, so I can come back to them later. Has worked well so far.EDIT: Just checked: I got my last transistor deliveries from "Kechengwei Store" and they were all genuine.They also have some amazing SMD assortment kits in stock for a great price. I just basically got all their 0402/0603/0805 and 1206 kits for resistors and capacitors a while ago and now I never have to worry about having a fitting SMD part in stock, quite handy. And loads cheaper than those assortment books.

author: MathWizard
author_rank: Super Contributor
timestamp: February 26, 2024, 03:17:02 am
content: Mosfet's in audio, that's some type of class-D amplifier thing right ? I can't remember how class-D works, but yeah if you take cheap, low power jellybean mosfets, like even a 2N7000, how good/bad are they for audio, say vs jellybean BJT's like 2N2222, 3904, BC547 ?

author: DavidAlfa
author_rank: Super Contributor
timestamp: February 26, 2024, 05:06:10 am
content: Class D is basically high frequency PWM (Normally 250KHz+) driving the speakers.So they just switch on/off, no ohmic/active region here.

author: ErinBob
author_rank: Newbie
timestamp: February 26, 2024, 05:34:21 am
content: So I'll ask here only because it's relevant to what I'm doing but If I only have multi meter and common electrical stuff how do I determine N or P type MOSFET? And 250khz? Are they all that fast or do I need special type there?

author: ErinBob
author_rank: Newbie
timestamp: March 04, 2024, 06:24:48 am
content: Would this one work to replace it?Bridgold 10pcs IRF3205PBF IRF3205 3205 N Channel Power MOSFET Transistor,110 A, 55 V, 0.008 ohm TO-220AB

author: Jwillis
author_rank: Super Contributor
timestamp: March 05, 2024, 12:00:01 am
content: Quote from: ErinBob on February 26, 2024, 05:34:21 amFor testing Through Hole Power Mosfets. For small MOSFETs the pin orientation may be different. To determine orientation, with multimeter in diode test, connect the probes to different pins until you get a voltage reading of the body diode.Body Diode reading can anywhere between 0.3V to 1V depending on MOSFET. Those 2 pins are the Drain and Source Small MOSFETs the gate is usually the centre pin.Set your multimeter to diode. With the pins toward you, Power MOSFET pin orientation will be from left to right Gate Drain Source. For this test "Clip" = "Probe"Take appropriate ESD precautions.N-ChannelAttach the Multimeter Positive to Drain and Negative to Source.For N-Channel you should get a reading OL . If you get a reading then it's the body diode and it a P-channel. Go down to P-Channel testingWith Negative Source clip attached move the Positive Drain clip to Gate. This will charge the gate. Then move that clip back to Drain. You should get a voltage reading at 0V or near 0V. With finger and thumb, touch the gate and source pins. Reading should go to OL again.P-ChannelAttach the meter clips Positive to Source and Negative to Drain.For P-channel you should get a reading OL. If you get a reading then it's the body diode and it's N-Channel. Go to N-Channel testing.With Positive Source clip attached, move the Negative Drain clip to the Gate. This will charge the gate. Then move the clip back to Drain. You should get a voltage reading of 0V or near 0V. With finger and thumb, touch the Gate and Source pins. Reading should go back to OL againFor very large MOSFETs you can use a 9V battery to charge the gate. A used 9V battery will also work.Simply determine what polarity the Drain and Source clips should be attached to pins according to the previous test. Take 9V battery and touch the Gate and Source. By changing the orientation of the battery, the transistor will turn On or Off (OL) when you observe the multimeter.Do Not use a 9V battery on small MOSFETs as some have very low VGS and could be damaged. For small MOSFETs, simple using your finger and thumb from gate to either the source or drain is plenty enough to charge and discharge the gate.If any of these procedures fail then recheck with the Ohms setting to see if the MOSFET is shorted.I train many people in my field and tend to be very precise and repetitive. Don't take it the wrong way.

author: MathWizard
author_rank: Super Contributor
timestamp: March 05, 2024, 02:34:46 am
content: IDK any safe or easy way to test up to 110 amps, that's some pulse current I guess too. IDK what the stereo really needs, but if you aren't cranking the power up too high, there's probably a lot of mosfet's that would be fine as a stand-in, at least for a while, or just as a test. But yeah you would probably want something with similar small signal characteristic's, especially if it's driven at up around 250kHz. Some of the mosfets should say "for audio" too.Some of the test circuits for testing mosfets might be worth a try, just to see what the other mosfets act like. To you have a scope or any hobby/repair parts to make a little circuit, even just to see the gate-source turn-on voltage, that's a pretty easy circuit.There's lot IDK about mosfet's still. Like 1 time, when testing mosfet's, with a good bench PSU, I've had a hard time getting the current in them, to decrease, even after turning the gate voltage way down. Probably for some semi-conductor physics reasons, I don't think it was the PSU.

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 05, 2024, 05:20:15 am
content: Probably yes. I don't think that device uses state-of-the-art transistors.