Is this pcb board screwed? Blew a capacitor on this analytical balance scale.  - Page 1
Forum section: electronics / repair

author: artvandalai
author_rank: Regular Contributor
timestamp: December 24, 2024, 01:17:05 am
content: Blew this capacitor plugging in wrong power plug on this analytical balance scale. Nothing else looks blown or burnt. Is this analytical balance scale salvageable once i replace the capacitor or is the pcb board most likely screwed?. I could not locate any fuse to protect the pcb board from over voltage.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 24, 2024, 01:27:48 am
content: One experiment is worth 1000 expert opinions. Replace the capacitor and see if it works. Was the wrong supply the wrong voltage or wrong polarity? Maybe that capacitor acted as a fuse and saved the rest of the board.

author: artvandalai
author_rank: Regular Contributor
timestamp: December 24, 2024, 01:37:19 am
content: Hey thanks for your opinion. I will definitely be replacing the capacitor, just wanted to get further opinion from knowledgeable members if there might be further damage to the board.

author: inse
author_rank: Super Contributor
timestamp: December 24, 2024, 01:45:57 am
content: I agree to Jpanhalt.Caps don’t blow immediately, leaving a chance for other stuff to get destroyed.There appears to be a step down converter right hand of the blown cap, hopefully this has proteced the precious electronics.Remove the cap and measure if the supply is still shorted, if so also remove SMPS controller, if still, deeper investigation will be necessary.Wait a little with replacement ordering, maybe more adds to the shopping cart…

author: tggzzz
author_rank: Super Contributor
timestamp: December 24, 2024, 01:47:07 am
content: Which capacitor?What is the difference the two plugs: polariy, voltage, current capacity?

author: inse
author_rank: Super Contributor
timestamp: December 24, 2024, 01:49:01 am
content: Quote from: tggzzz on December 24, 2024, 01:47:07 amObviously top center of the first photo.

author: fzabkar
author_rank: Super Contributor
timestamp: December 24, 2024, 02:23:53 am
content: https://www.analog.com/media/en/technical-documentation/data-sheets/117012fi.pdf

author: wraper
author_rank: Unknown
timestamp: December 24, 2024, 02:41:10 am
content: What is PSU output voltage? I don't see any voltage regulators other than opamp bipolar supply. So I suspect digital ICs may be powered directly from PSU. If that's the case (5V), then yeah, I think replacing the cap and applying power would be correct thing to do. If there are VREGs, then I would check first if they don't have shorted in-out to be safe.

author: u666sa
author_rank: Frequent Contributor
timestamp: December 24, 2024, 03:03:04 am
content: Several things look suspect on this board.

author: artvandalai
author_rank: Regular Contributor
timestamp: December 24, 2024, 04:36:59 am
content: Ill check again but some of what your pointing is from the blown capacitor. It spewed some kind of liquid when it blew.

author: artvandalai
author_rank: Regular Contributor
timestamp: December 24, 2024, 04:47:38 am
content: I removed the capacitor and there seems to be continuity to the components down the board from the power plug

author: inse
author_rank: Super Contributor
timestamp: December 24, 2024, 05:08:46 am
content: Sorry, I didn’t get it… Is the power supply input shorted?Then remove the SMPS chip on the right side of the transformer

author: wraper
author_rank: Unknown
timestamp: December 24, 2024, 01:01:40 pm
content: Quote from: u666sa on December 24, 2024, 03:03:04 amIC is suspicious. But those are just flux residues from hand soldering around the transformer.

author: DaJMasta
author_rank: Super Contributor
timestamp: December 24, 2024, 08:45:54 pm
content: There look to be some singed vias lower right of the cluster of capacitors, haven't seen that before, maybe it's a figment of the lighting. It's entirely possible something else is a problem, but the capacitor is the place to start.If you have a lab power supply, remove the cap and connect the power supply with a severely limited current (100-200mA maybe) and check for heating of parts, that could be done before a replacement is available. If you've got a parts bin with a somewhat comparably rated capacitor, you could put it in temporarily and see if it comes back to life.

author: artvandalai
author_rank: Regular Contributor
timestamp: December 25, 2024, 05:42:13 am
content: Will any 100 µF 40 V aluminum electrolytic radial capacitors be compatible? Im unable to find a similar capacitor on digikey or mouser.

author: inse
author_rank: Super Contributor
timestamp: December 25, 2024, 05:57:38 am
content: Most probably any should fit, you can verify at the manufacturers website what series it‘s from:https://www.cosonic.com/spec-ecLooks like the orange ones are standard low leakage types

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 25, 2024, 06:10:32 am
content: The capacitor did what is written on it.Based on the issues on the board pointed out by u666sa, I would first look into the ic right next to the transformer. There is damage on the top of it. Could not find any information on either the 94Q, 940 or 1172 marking that matches this ic.Best to investigate that further before replacing the cap and applying power again.

author: inse
author_rank: Super Contributor
timestamp: December 25, 2024, 06:39:06 am
content: LT1172 switching regulator as mentioned already 😉

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 25, 2024, 07:34:13 am
content: Quote from: fzabkar on December 24, 2024, 02:23:53 amQuote from: inse on December 25, 2024, 06:39:06 amYes you are right, but a bit "under mentioned" I would say, just a post with a link, is what I skipped to look at.A bit weird that a search for "smd marking 1172" does not show anything on the LT1172.A search for "1172 switching regulator" does work wonders though.

author: inse
author_rank: Super Contributor
timestamp: December 25, 2024, 07:53:22 am
content: The LT logo is visible though 😉

author: artvandalai
author_rank: Regular Contributor
timestamp: December 31, 2024, 12:07:16 pm
content: Is the ic a LT1172cs8 model? It has the same dimensions as the one on my board. What does the 940 numbers mean on this ic? if the smd components further down the pcb board from the blown capacitor have continuity starting from the power input to those components does that mean they are not shorted or blown including this ic?

author: artvandalai
author_rank: Regular Contributor
timestamp: January 07, 2025, 12:49:05 am
content: https://www.digikey.com/en/products/detail/panasonic-electronic-components/EEU-FC1H101/266332An update on this, Ive replaced the capacitor with one of these panasonic 100 µF 50 V and the scale didnt turn on

author: inse
author_rank: Super Contributor
timestamp: January 07, 2025, 01:40:33 am
content: Quote from: artvandalai on December 31, 2024, 12:07:16 pmYes, most probablyQuote from: artvandalai on December 31, 2024, 12:07:16 pmManufacturing date code 1999/2009/2019 - week 40Quote from: artvandalai on December 31, 2024, 12:07:16 pmSorry, don’t understand.Does anything run hot?Did you check the presence of supply voltages?Make yourself a principle schematic of the power supply structure - where does the 12V input go to?Sorry, we will not be able to give a complete repair instruction from afar, you will have to investigate by yourself.Is asking the supplier for repair an option?

author: fzabkar
author_rank: Super Contributor
timestamp: January 07, 2025, 02:33:08 am
content: Quote from: pcprogrammer on December 25, 2024, 07:34:13 amSorry, I should have shown you my search methods:http://markingcodes.com/search/c/1172https://www.google.com/search?q=filetype%3Adoc+OR+filetype%3Apdf+%22absolute+maximum%22+1172+converter

author: beenai2018
author_rank: Contributor
timestamp: January 14, 2025, 06:06:08 pm
content: It may be necessary to clean out the capacitor goop that spilled out on the board. 91% IPA(or higher) works for this. Please check after cleaning and fully drying out.The LT1172 SO-8 should have a small current sense resistor nearby . Those may also provide test points to see if the converter is working .Please check the datasheet.Its hard to tell from the photos but if there are pinholes in the lt1172 then its probably gone and needs replacement.

author: artvandalai
author_rank: Regular Contributor
timestamp: January 14, 2025, 09:17:01 pm
content: I did not see any pinholes in the switching regulator but im still going to replace it once the part arrives as changing the capacitor didn't help out

author: artvandalai
author_rank: Regular Contributor
timestamp: January 16, 2025, 10:28:16 am
content: It was the voltage regulator chip. I replaced the chip and now the scale works.

author: inse
author_rank: Super Contributor
timestamp: January 16, 2025, 10:37:07 am
content: Perfect, cheers!