Need help to identify burned smd component  - Page 1
Forum section: electronics / repair

author: Alex_ulli
author_rank: Contributor
timestamp: October 31, 2024, 01:43:59 pm
content: I have a tennis ball machine working from 18V battery. It doesn't switch on anymore, I opened it and there is one burned component on the PCB (top right corner of the board, next to the power input), it seems like it should be some kind of stabilizer, but I can't see what was the marking on it - just the remains of the last two digits - "43"(not sure about it). So if anyone can help me with identifying that component or a replacement - it would be great. Thank you!

author: picburner
author_rank: Frequent Contributor
timestamp: October 31, 2024, 02:26:38 pm
content: The silkscreen says "Q10" so it is not an IC but probably a mosfet in SO-8 package.To have a clearer idea of ​​the type of device you should draw a rough schematic of that section.

author: Alex_ulli
author_rank: Contributor
timestamp: October 31, 2024, 03:27:28 pm
content: This is a multilayer pcb, so I can't see connections between elements. I only can measure resistance between some points, not sure if this will help:(The only thing I can say for sure - the first 3 inputs to the missing element (mosfet?) are connected to +18DC directly.Any thoughts?..

author: picburner
author_rank: Frequent Contributor
timestamp: October 31, 2024, 03:40:16 pm
content: That connection could indicate a P-channel mosfet.But to be sure, you would need to investigate the connections further.

author: picburner
author_rank: Frequent Contributor
timestamp: October 31, 2024, 05:57:04 pm
content: I was just only focusing on your request before.Now, looking at the rest of the board, I see that Q41 and Q42 also have burn marks on them.Unless it's just an optical effect, it might be a good idea to check for other damage before doing any replacements.

author: Alex_ulli
author_rank: Contributor
timestamp: October 31, 2024, 06:30:44 pm
content: Yes, I didn't notice that they are probably burned, thank you. At least they have some heat damage. But that's easy - I can read marking on them. And anyway, they are in the circuit of one of the motors, without them I should see the board is alive. At this moment, it is fully dead, I believe because of the Q10.

author: unseenninja
author_rank: Regular Contributor
timestamp: October 31, 2024, 06:51:11 pm
content: What are all the green fibres all over the board about?

author: Alex_ulli
author_rank: Contributor
timestamp: October 31, 2024, 06:53:32 pm
content: Those are fibers from tennis balls.

author: pcprogrammer
author_rank: Super Contributor
timestamp: October 31, 2024, 06:55:31 pm
content: Quote from: unseenninja on October 31, 2024, 06:51:11 pmSome rub off from tennis balls most likely.Quote from: Alex_ulli on October 31, 2024, 01:43:59 pm

author: pcprogrammer
author_rank: Super Contributor
timestamp: October 31, 2024, 07:00:46 pm
content: The death of Q41 and Q42 is most likely the cause that Q10 died as well.Make sure that what Q41 and Q42 are driving is in proper working order again. Maybe a wedged ball led to a current spike that killed those MOSFET's

author: unseenninja
author_rank: Regular Contributor
timestamp: October 31, 2024, 07:03:12 pm
content: LOL, I missed the "tennis ball machine" part of the story!Thankfully, this doesn't seem like an application where leakage is critical.

author: Alex_ulli
author_rank: Contributor
timestamp: October 31, 2024, 07:28:11 pm
content: Yes, maybe that was the reason. Q41 and Q42 are driving the bottom motor for the balls. It feels and looks good right now, but maybe some ball stuck while somebody from the family was using it.So since the machine is already broken anyway - I will try to guess what to put instead of this Q10. If anybody can make a suggestion - I will have a shot. Right now I ordered this onehttps://www.ebay.com/itm/134450995007

author: fzabkar
author_rank: Super Contributor
timestamp: October 31, 2024, 07:28:51 pm
content: Quote from: Alex_ulli on October 31, 2024, 06:30:44 pmSTL56N3LLH5https://www.st.com/resource/en/datasheet/stl56n3llh5.pdf

author: picburner
author_rank: Frequent Contributor
timestamp: November 01, 2024, 04:40:28 am
content: Quote from: Alex_ulli on October 31, 2024, 07:28:11 pmIFR7404 has a Vdss of -20V, a too narrow margin for a 18V battery supply.I suggest you look for a device with 30V Vdss like the rest of the power mosfets mounted on your board.

author: pcprogrammer
author_rank: Super Contributor
timestamp: November 01, 2024, 07:07:17 am
content: And one that can handle a lot more current. The STL56N3LLH5 can handle 56A. This does not mean that this current is actually flowing, but they did choose these MOSFET's for a reason.The Vishay SI4497DY-T1-GE3 might be a better match.https://www.vishay.com/docs/65748/si4497dy.pdf

author: Alex_ulli
author_rank: Contributor
timestamp: November 01, 2024, 02:17:48 pm
content: Quote from: pcprogrammer on November 01, 2024, 07:07:17 amThanks, ordered them also.

author: Alex_ulli
author_rank: Contributor
timestamp: November 01, 2024, 03:26:39 pm
content: Quote from: fzabkar on October 31, 2024, 07:28:51 pmYeah, and can somebody advise where I can buy them? I found on ebay from 1 seller for 10$ each, I need 2 and it seems like too much for an experiment.first 20 links in google - they are not sellers actually, I even made an order herehttps://www.newark.com/stmicroelectronics/stl56n3llh5/mosfet-n-ch-30v-56a-150deg-c-62/dp/69AH2760?CMP=e-email-sys-orderack-GLB,but it turned out that they don't have item in stock, and it can be shipped only next year;)

author: Sensorcat
author_rank: Regular Contributor
timestamp: November 01, 2024, 09:42:23 pm
content: Quote from: Alex_ulli on November 01, 2024, 03:26:39 pmhttps://www.digikey.com/en/products/detail/stmicroelectronics/STL56N3LLH5/2756447?s=N4IgTCBcDaIMoBUAyBWAbAOQMxKQCRRAF0BfIAQuote from: Alex_ulli on November 01, 2024, 03:26:39 pmGoogle search is not ideal if you already know manufacturer and part number, better go directly to a distributor, like in the example link above. Using an industry distributor has the advantage that you can be quite sure to get the genuine part, unlike ebay and other platforms where anybody can set up a small business to sell anything.

author: Alex_ulli
author_rank: Contributor
timestamp: November 01, 2024, 10:30:34 pm
content: Quote from: Sensorcat on November 01, 2024, 09:42:23 pmYes, thank you. I already placed an order here. Earlier today, I had some trouble with them; for some reason, they were canceling my orders. But I resolved it over the phone. I was hoping there was a faster way, than a week of expectation.

author: Alex_ulli
author_rank: Contributor
timestamp: November 05, 2024, 07:22:29 pm
content: Good news, guys!Thanks everyone for help one more time!So, I received first ordered item - IRF7404 Mosfet P-Channel 20V 6.7A. Yes, I understand that 20V is too close to 18, and I will replace this Mosfet after I will receive the recommended one. I just wanted to test without full load, and I assumed it should work. And it did!Now, I can switch on my machine and everything seems to be working, except, of course, one bottom motor, which I didn't connect.What I've noticed is that in this circuit for the bottom motor - something is heating very fast, in one second after switching on. It seems like this part, that I circled on the photo. What might it be? Do you think it is because of the burned components in this circuit? Don't want to have new components to burn again.

author: pcprogrammer
author_rank: Super Contributor
timestamp: November 05, 2024, 07:37:32 pm
content: Looks like a capacitor. Can you figure out how it is connected in the circuit?

author: Alex_ulli
author_rank: Contributor
timestamp: November 05, 2024, 09:20:24 pm
content: Quote from: pcprogrammer on November 05, 2024, 07:37:32 pmI am afraid it is impossible to find out how it is connected. So only to hope that everything is ok, except those mosfets. Anyway I ordered 4 of them, just in case

author: u666sa
author_rank: Frequent Contributor
timestamp: November 05, 2024, 11:12:08 pm
content: Those mosfets are shorted to ground, that's why that cap is getting hot. Remove mosfets, check cap for short.

author: fzabkar
author_rank: Super Contributor
timestamp: November 05, 2024, 11:42:12 pm
content: Quote from: u666sa on November 05, 2024, 11:12:08 pmIf a capacitor is heating up, it's because it has become ohmic. I would measure its resistance in and out of circuit.

author: picburner
author_rank: Frequent Contributor
timestamp: November 06, 2024, 05:50:01 am
content: In addition to the capacitor problem, replacing the STL56N3LLH5 burned mosfets will be a complicated undertaking if you don't have the right equipment (hot plate, hot air/IR desolder) as they have a large pad underneath them soldered to the PCB.All the close-packed components further complicate the task, you will need to isolate the part you are replacing with Kapton tape to prevent other nearby components from flying off.Anyway, at least, the device is turned on now!

author: Alex_ulli
author_rank: Contributor
timestamp: November 06, 2024, 03:50:48 pm
content: Quote from: picburner on November 06, 2024, 05:50:01 amI've noticed that too, but thank you for mentioning it. While I'm waiting for the MOSFETs to ship, I'm checking Facebook marketplace to buy a used soldering station with hot air. I've already ordered solder paste with a melting point of 138°C (do you think it's suitable for this job?)https://www.amazon.com/dp/B0BLSKZ6W1?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1.It's been a while since I was into this stuff, and technology and soldering equipment have advanced a lot, so thank you again for all the advice, I really appreciate it!

author: Alex_ulli
author_rank: Contributor
timestamp: November 10, 2024, 03:39:39 pm
content: So,I desoldered the capacitor that was previously heating up and checked it with an ohmmeter—everything looked good. I reinstalled it and then desoldered those burnt MOSFETs (which wasn't easy, by the way).After reassembling everything, it worked! However, I noticed that both circuits for the main motors are heating up slightly, the current might be too high by design. Not sure how long it’ll keep working, but we'll see. I have some spares ready for replacement if needed.As for the power input circuit, I left a 20V MOSFET in place because it's working fine and isn't heating up, so I decided not to touch it for now.Thank you for your help!