A loud bang that did nothing? - Page 1
Forum section: electronics / repair

author: Artlav
author_rank: Frequent Contributor
timestamp: September 01, 2015, 10:31:56 pm
content: Here is an average noname small monitor.It's rated for 12V DC.I screwed up and plugged it into 24V.Surprisingly, it worked without a problem for several minutes.But then there was a loud bang.At which point i unplugged it, looked around and realizedwhathave i plugged it into.So far, typical.But the strange part is, it still works just fine.There wasn't any smell of the magic smoke escaping, all the functionality is still there, there are no glitches or anything.The survival is not too surprising - the power input is going straight into a pair of ACT4060A DC/DC chips, and they have 28V absolute maximum and up to 24V nominal.The thing is supposed to go into a car, so i guess they expected some transients.The question is - what made the bang then?I suspect it might have been a capacitor venting, but i checked them all and they all appear to be fine.Can anyone see anything blown or whatever could have made a bang?Hi-res main board:Back:Front:The screen part contain only the panel and a PCB strip with buttons, nothing else.Backlight supply is on the main board, and is after the input DC/DCs.

author: xrunner
author_rank: Super Contributor
timestamp: September 01, 2015, 10:36:35 pm
content: Did the external power supply go bang?

author: Deathwish
author_rank: Unknown
timestamp: September 01, 2015, 10:38:04 pm
content: Top right hand corner of the front of the pcb next to the 27 Ohm resistor, the cap looks like it has vented at the pin leads.

author: kingofkya
author_rank: Regular Contributor
timestamp: September 01, 2015, 10:45:51 pm
content: Yeah i agree cap looks like it blew out the bottom.

author: Artlav
author_rank: Frequent Contributor
timestamp: September 01, 2015, 10:57:25 pm
content: Quote from: Deathwish on September 01, 2015, 10:38:04 pmQuote from: kingofkya on September 01, 2015, 10:45:51 pmIndeed it is... And i was only looking at the tops.Thanks!Quote from: xrunner on September 01, 2015, 10:36:35 pmNo, the bang would have been from a completely different direction then.

author: EEVblog
author_rank: Unknown
timestamp: September 01, 2015, 11:15:48 pm
content: Quite funny that it blew the bottom instead of the top vent. Poorly designed cap!

author: tautech
author_rank: Super Contributor
timestamp: September 01, 2015, 11:22:12 pm
content: Quote from: EEVblog on September 01, 2015, 11:15:48 pmI've seen this a few times from over-voltage events to the extent flying cans could take an eye out.

author: TSL
author_rank: Regular Contributor
timestamp: September 02, 2015, 05:35:34 am
content: Quote from: tautech on September 01, 2015, 11:22:12 pmNot wrong there! - Many years ago when I was repairing old Taxi radios, the hybrid type with valves in the output stage, I mistook a 6.3V cap for a 63Vcap to be replaced in the driver stage.I was leaning over the radio when I powered it up and the resulting bang sent the cap up and ricochet off my chest.It left a nasty bruise & scared the crap outa me. It popped like one of those party streamers! - what a mess.I blame it on the bourbon the night before

author: vk6zgo
author_rank: Super Contributor
timestamp: September 02, 2015, 06:08:57 am
content: Replacing Electros in a -24 volt supply---lost track of what I was doing,& wired them -ve lead to ground.Turned it on,and,"Bang!!"The Transmitter Speech Input room looked like it was snowing capacitor guts!On another occasion,a Trainee was building up a Dick Smith kit.He gave it to me to check he had all the caps the right way round---all good,according to the silkscreen.He connected power -----------BANG!Dear old "Dicky" had printed the silkscreen wrong!It happens in the best of families,though---Sony did the same with a 14" Broadcast Standard Picture Monitor.Only on one side,though---it was marked on both.More recently,I was using a Noise Bridge,& somehow forgot what I was doing & transmitted into it.Expecting the worst,I checked it,& it still works-----the windings on the "binocular" ferrite look a bit singed,though!

author: timb
author_rank: Super Contributor
timestamp: September 02, 2015, 09:01:41 am
content: Quote from: TSL on September 02, 2015, 05:35:34 amDid the same with a 1960's era Fluke calibration standard. Replaced an electrolyte on the chopper amplifier board with a 6.3V by mistake.Amazingly it ran for nearly 10 seconds, making this pulsing noise. The pulses got quicker and quicker until I heard (what I thought) was a gunshot. Then the side of my head started to burn, after touching it and seeing blood all over my hand I was pretty sure I *had* been shot.Nope. Capacitor shrapnel left a small cut on the top of my ear. It wasn't even a small cut, tiny better describes it, but by the amount of blood coming out you'd have thought someone glued a grenade to my ear and pulled the pin.Sent from my Tablet

author: tautech
author_rank: Super Contributor
timestamp: September 02, 2015, 11:36:08 am
content: Quote from: TSL on September 02, 2015, 05:35:34 amI had a cap pop in an old ATX PC PSU and on investigation the insides where unrecognisable due to the mess.Quote from: timb on September 02, 2015, 09:01:41 amBut I shouldn't laugh, this stuff is a serious risk to us hobbyists and technicians.We're the lucky ones IMO to have escaped with minor injuries, one must be bloody careful with caps when undertaking repairs and servicing.I've taken to NEVER having a part of me directly above a PCB after repairs, it's not worth the risk.I do know that since I've been using a dim bulb tester I've never had a cap blow, faulty or freshly installed.

author: mikerj
author_rank: Super Contributor
timestamp: September 02, 2015, 02:51:08 pm
content: Quote from: EEVblog on September 01, 2015, 11:15:48 pmProbably not so surprising with the cap mounted sideways like that. If it was mounted as intended the PCB would prevent rubber seal from being pushed out and the scored end of the can would probably have ruptured instead.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 02, 2015, 03:05:30 pm
content: Quote from: EEVblog on September 01, 2015, 11:15:48 pmMost small caps are intended to fail that way (hence the rubber base insert, and lack of relief on top), but this one even had the relief pattern...I'm surprised it didn't let out the confetti though.Tim