Does A Short Circuit Mean Something Is Faulty? When is a short not a SHORT.
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- Опубліковано 10 лис 2023
- Often when fault finding, your mulitmeter will read short. Sometimes this indicates a faulty component, but sometimes it doesn't. How to work out if the short is really a short? Watch this video and you will learn how I often work out what the multimeter is trying to tell me
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Thank you
Richard
*I spoke with Dan over in Lanzarote this morning (he sent me the amplifier). After watching the video he tested the speakers. So the bass driver speaker coil had basically melted, it had welded itself into the magnet. The tweeter coil has blown apart. We had a chat about what could have caused this, apparently he got the speaker new from Thomann. kept it in stock for about six months and had only been installed and in service for a couple of nights. They have an audio level limiter in the bar so it could not have been driven too hard. It's hard to work out what caused the fault, apparently it was making strange sounds intermittently before it failed*
Just thinking out loud, but maybe a speaker ohm mismatch? Thx.
Since you are located near equater, popping set into & out of cool gig locales probably allowed condensation to form. You showed odd moisture marks on PC board.
@kendoty2463 And if it came from the other side of the equator, the current would have flowed in the opposite direction, like flushing a toilet ;)
@@mikecro1111 , maybe hemispheres... 🙂
You can not teach experience you have to earn it by lots of practice and recognising circuits. You make perfect sense with that board and explain it well.
Thanks Tony 😄
You've gotta great British teaching technique, believe me😉
Exactly how I like it.
Down to earth, confident & fantastic fault finding style 😎😉
Can't thank you enough for these videos ive probably watch around 60 hours of videos so far. Its really excelled my confidence in electronics.. I've brought a graphic card to work on its the same model as mine so i have something to compare with, will do that till im confident to work on different cards thanks again Richard
Thank you very much from Sweden!
I want to thank you for your videos. I've been out of touch with electronics for quite awhile.
I was a robotics tech for Seagate. I'm retired now from construction/handyman/Railway Fireman.
I appreciate reacquainting and bringing me up to date!
Have a good one,
Mark
You're welcome. enjoy
The title of this video really caught my eye.... I watch your videos very carefully especially when you are probing around components, and I really am studying the resistance readings you get... And I'm trying to gain experience based upon those numbers for learning what the next step might be when you find suspicious or curious readings. And it looks like at some point when you think you might have discovered the problem it's time to go look up the component in question and use that information to see if the readings are what they should be based upon the internal structure of the component or is that component defective based upon reading the components inputs and outputs. I think you know what I'm getting at, as far as fixing something quickly I think overall... what we do here that's not particularly important, what is important is over time developing good techniques that will get the device being repaired diagnosed and fixed. Also I am constantly seeing components that I haven't seen before and learning the purpose of that component being designed that way and how it is used in a circuit. It's Great information.
Thank you. Yeah basically it's a mixture of
1. understanding what the basic layout of the circuit will be ,based on what it is (in this case two class D amplifiers it turned out)
2. Using datasheets to know what components you are looking at when you have some 'suspicious' readings
thank you for your videosthey reaally help me alot
Amazing explanation!
Great video. Thank you
Brilliant, thank you so much for sharing your knowledge and experience. For me that was very easy to follow.
I saw on the PCB the marking "94V-0". Ends up it's a rating ... "meets the highest flammability standards and can withstand harsh environmental conditions. I wonder if anyone has every confused that with 94volts?!! Thx for the video. Love it when you draw/explain the circuits. Cheers.
Yeah first time I noticed that was on an old motherboard, I went onto Vogons (retro PC forum) and asked for a user manual for 94V-0 😂
As you rightly say, it's a fire safety rating, a bit like IP66 is a water/dust proof rating. I suspect someone sometime did mistake it for 94 Volts.
Thanks for the videos you make, I work with electronics, but I have the luxury to replace each board if I don't know where the fault is going on. I hope some day I would learn the fault finding skills that you have. When I listen to you explain it all makes sense, but on paper I have hard time getting around those + and - and ground, can't figure out why they are the way they are on the board. Anyways hats off, your skill is insane and your channel a hidden gem!
It's not hidden anymore! eveyone knows now
@@roseelectronics4582 Yeah, It has been noticed LOL 🤣
Thanx Sir
Outstanding, sir. I'm trying to repair a newer subwoofer amp with no schematic & this helps me a lot. It's essentially the same design as what you have there but of course only one output. Thanks for sharing your work.
good video
Please give us more knowledge about active speaker, how to find faulty parts
@ 1:04 ok ill comment Richard lol
Heya, oke the mosfet is short but how does that blow the fuse ? low and high site are separated by the isoptilazer and the transformer
Whatever wattage is dissipated in the low voltage side will also be dissipated in the high voltage side (assuming 100% efficiency). So a high current due to a short on the secondary side causes a high current on the primary side, hence the fuse blows
Keep in mind Rick that all these biamped powered stuff have (almost always) a single volume knob. This specific item is an RCF product. A good choice for your client but needs to be protected from moisture and salt. A newer model this one. I've used older models of RCF for years in nasty environments and hard work, no problems.
I have an issue with a similar board setup, there's a -24v reading on the tweeter terminals, the mosfet keeps blowing for that amp or that mosfet and the SMPS power fets blow, there's no shorts and the driver chip is working????
hello Richard, you have Avast wealth of knowledge which has experience with the trade and capable of tackling large tasks. gained through experience i have none you are a good teacher.?
Why does the fuse on the primary side blow if the short is on the secondary side? Aren't they electrically isolated? Cheers
How can he be measuring voltage when its not connected to any power bench supply?
All that white residue on the board seems weird, a foam party or two way too much maybe 😄
@ 39:00 you are thinking the same is me same mind set
@10:04 bit of both I think but lets caal that luck 🙂
@6:43 ayayay looks like it had a river flowing inside did he use it in the swimmingpool ?lol
Amazingly it's a brand new speaker. Maybe 10 hours use inside. Have no idea how the board looks like that. No moisture residue anywhere else.
My biggest issue is my memory. I think I have forgotten more than I remember over the years and then don't come across a similar issue again for years; and I have to re-teach myself over and over again. Multilayer boards are also the bane of my existence these days.
I followed the video well. I am not sure though (and I may be wrong) if you have done a beginners video where you talk about the classes of amplifier circuit and how to quickly identify them - this might help to bridge the slight gap in knowledge for those who are newer to amps.
Also, As you get more and more videos on your channel it may become more advantageous to break the playlists down into smaller sub-categories. 👍
I think the video you are referring to is 'All You Need To Know About Amplifiers To Fix Stuff'. My memory is about as good as yours 😅
@5:38 A fuse does not blow without a reason so something more is going on... lets see if you think the same Richard
There may be some teaching value to know that if I don't find a short in the primary power supply side I jump straight to the power transistors, then the secondary power supply side. But I suppose with the deeper understanding you provide, your "pupils" will soon come to the shortcuts themselves.
How about the speakers? Should your customer measure them before he reconnects the amp?
Spoke to the owner. See the pinned comment for an update
yup you did think the same hahaha
Plz make some videos on telephone repair (land line phones not mobiles...)
To be honest I don't even have a land line to work on them.
@@LearnElectronicsRepair 🙂
Watched again. Got confused around ~38mins when you determined that the speakers were being driven by inductors ... inductors resist change (AC), so that's odd to me as speakers should receive AC ... and so I'm lost.
Ahh yeah. So the class D amplifier is not like a linear Class AB amplifier. It's much more like a switch mode power supply and uses PWM (pulse width modulation) to drive the speaker. The PWM is modulated by the audio signal, so what comes out of the pair of mosfets are high frequency square waves (hundreds of KHz) that 'carry' the audio signal. The inductors then filter out the high frequency carrier and what you are left with is audio frequency signal up to about 22KHz. The advantage of this method of amplification is that the mosfets are only ever on or off, so you don't need large heavy heat sinks and cooling fans. Does that help you understand it better?
@@LearnElectronicsRepair , yes indeed! TY! I am weak on amplifier classes, so need more study. I'm going to look for an oscilloscope screen video showing the PWM carrier with the audio signal in tow for better understanding. But, very helpful. Thx! Cheers
29:57 it is a amp LOL
When it's a long 😂
Yeah really when is it a "long"
@@roseelectronics4582 When it's hard to find 🤣 Do you know how to keep some one in suspense too ?
where is MR.Bleep to look for shorts ?
Ok so it was me who sent in the amp. It was from a brand new speaker that had done at most 10 hours work inside. How the board got in that state i have no clue but there is no evidence of moisture anywhere on the speaker. I have now checked the drivers and both are blown. The low frequency voice coil is melted together. HF is blown apart. Customer said it started cutting out then went off. The other speaker is still in service and has had no problem.
They have the fire extinguished with lots of beer