As a relative noob I did have to go back over the section where you homed in on the resistor but this was incrediby useful both from using the 'scope to see the difference on inputs and the voltage tracing to show the differences between good and bad channels. Kinda lucky having working channels to compare against though!
I had a lucky guess when you were measuring the resistors in circuit, but it wasn't until you drew it out that I understood why, I think 😜, so your time was very well spent and made all the difference for me. Thank you 😊
I think you spent the exact correct amount of time explaining the diagnosis... Even if I was screaming "YOU CAN'T HAVE A ZERO VOLTAGE DROP ACROSS A POWERED RESISTOR" at my screen for 5 minutes starting at 10:28.
Good fix and fault finding, i appreciate the drawing you make to explain the fault at least with an open resistor you can read its value unlike a burnt resistor and it came up easily with a soldering iron even from one end
Well done Rick. When you started writing the voltages on the schematic I was fooled to think that the lowside mosfet was somehow shorted. It seems that experience and perseverance always wins over clever newbies like me. On the other hand the owner reminds me of hundreds of other dudes of the same kind that I met year after year installing audio and lighting systems. They never change.
20:10 - 33:08 This is classic troubleshooting technique from knowing nothing to locating the fault. I’m happy with the way you troubleshoot out loud. Your thinking processes are laid on the table for all to see! I don’t work on amplifiers; but, I can use your techniques to get a better understanding of circuit analysis methods to help me troubleshoot many of the things that hit _my_ bench without schematics! Thank you for showing us such detail from your work! I have learned much from you in the short time I’ve known about your channel and I’ve been doing electronics repair for many years by the seat of my pants!
Awesome work on explaining that. I was even able to follow you, not understand everything, but at least follow. I am sure the depth you go into explaining something is annoying to some, but for someone like me it's essential and assists so much more than you imagine. Keep them coming!!
As always another fantastic tutorial. Thank you for sharing your expertise with us. You are a gifted instructor. Hope you revisit your PWM lesson soon. I know you mentioned going into further detail with schematic drawings and such.
This was very cool as your title says if you see something that doesn't make sense read what your meter is saying and think about it. That resistor chain was so obvious. Well done great fix....cheers.
Cheers Paul. This the whole point of repair work, if you take measurements you have to analyse what the results are actually telling you otherwise they won't help you much, This kinda comes down to knowing what you expect before you take the reading and working out what the problem is if the readings don't match your expectations,
Just a quick question about measuring the duty cycle at the mosfets... as you're using your hand held oscilloscope it's obviously fully isolated. I only have my bench oscilloscope which isn't. Can you tell me it this would be a time that it would be necessary to use differential probes given the ground connection to the amp's negative rail? I'm trying to teach myself to repair electronics and obviously don't want to fry my oscilloscope by putting current down the ground connection! Excellent lesson in diagnosis of the fault and explanation of how the amp actually works.
timestamp 12:44 on the bad one when you have a higer voltage then the good ones on one side of the resister and no voltage on the other side of the resistor on the bad one ... then the resistor is open as there is no load.... it looks to be a voltage devider so with no voltage the chip can not run
Correct. I laboured the point a bit but that was for educational purposes. it was also worth checking tos ee if a short on the other end of the resistor had caused to to go open (though you may reasonably expect that to cause it to burn up too)
Hello, I'm happy to see the FNRSI portable oscillosope at work. 😁 You are lucky becouse that channel is broken, if it was one to the right or left .... . A lot of work must be done. Thanks for video.
Hi Richard, I was wondering if you could make a video on understanding net names/signals on boardview software, e.g, I2C, PPV3H, etc. because I don't understand what these mean
Nice workthrough... Said it'd be a resistor on that bloomin' daughterboard :) Can you try measuring the dead one now it's out of circuit and had some heatsoak from desoldering? Not sure if was just crappy components or dodgy soldering/end caps !
@@LearnElectronicsRepair the 3x10K replacement will be just fine, probably better than the others 😀The one I repaired 10 or so years ago in a similar fashion is still fine as I also didn't have exact SMD parts at the time, I said to myself I'll do the swap for SMD if it ever comes back in for repair again, and so far so good 😉
Yeah it was, it's 8 ohms. The amp was also tried with another 8 ohm speaker on the bench. Mismatched speaker impedance can damage an amplifier for sure, but it wouldn't cause this sort of failure.
Hi there, another great video from your academy....could you please explain why we measure higher voltage on the output of rectifier (without filtering capacitor) than we measure on the output of AC transformer? Thanks a lot.
You are seeing the higher voltage because of spikes and depending on if there is a load or not on your output the voltage will be higher then the rating.
If the output of the rectifier is connected to the large smoothing capacitor(s) then the voltage on the transfomer output is the 'average' or rather RMS voltage of the AC voltage and what you read across the output of the nridge rectifier is the peak voltage (Dc) as the capacitors will charge up to peak. So the output of the bridge DC is going to be around 35% higher than the AC voltage coming out of the transformer.
@@LearnElectronicsRepair Thanks, but I was talking about rectifier without filtering capacitor....even then is measured rectified voltage higher than secondary transformer voltage
@@petopeter4832 I don't know the exact reason for that but I suspect you have the same voltage on the output of the rectifier as you do have from the output of the transformer but your multimeter, which is probably 'true RMS' for AC is showing you a different reading to the one it shows you for full wave rectified DC as an artifact of the way the multimeter itself works. You scope would probably show you the same reading (less 2x voltage drop across the silicon rectifiers in the bridge. Take a dual channel scope, use one probe on the output of the transformer and the other probe on the output of the bridge and superimpose the two traces. Make sure you only connect scope ground to one point!
I often just put a "whatever, it's close enough and I have it on hand" component like a resistor while waiting for an order to arrive, because it's so common that it was another part that caused the resistor (or whatever) to blow that half the time I expect the replaced component to immediately blow again. No point in waiting for the perfect/correct part to come in the mail when you can keep diagnosing. I mean, use common sense and don't put a 1/4w resistor in place of a heatsinked wirewound power resistor, but there's nothing wing with parallelling 10 1-ohms together while waiting for that specialty 0.1 ohm to arrive.
So is the scope ground on the negative supply you said? I became worried about the shorting of the supply? I need to think further.... Your previous video somewhere was on the hot side- is that the difference?
Yes, on the negative side. This is chassis ground, not hot ground. In a previous video I proved that this amplifier (and probably all Class D amps) will have a single supply rail, in this case 150V, th-cam.com/video/qpY91f7OqNY/w-d-xo.html
that is why you need hot tweezers then you got that resistor off of there in seconds without damaging anything close to it !!!!!!! ... I keep telling get hot tweezers they are the tools of heaven !!!!
As a relative noob I did have to go back over the section where you homed in on the resistor but this was incrediby useful both from using the 'scope to see the difference on inputs and the voltage tracing to show the differences between good and bad channels. Kinda lucky having working channels to compare against though!
Usually with an amplifier you will have more than one channel so it's not as kinda lucky as you say 😉
I had a lucky guess when you were measuring the resistors in circuit, but it wasn't until you drew it out that I understood why, I think 😜, so your time was very well spent and made all the difference for me. Thank you 😊
I think you spent the exact correct amount of time explaining the diagnosis... Even if I was screaming "YOU CAN'T HAVE A ZERO VOLTAGE DROP ACROSS A POWERED RESISTOR" at my screen for 5 minutes starting at 10:28.
Yeah it wasn't quite zero but it wasn't very much
:)
Good fix and fault finding, i appreciate the drawing you make to explain the fault at least with an open resistor you can read its value unlike a burnt resistor and it came up easily with a soldering iron even from one end
Will have to watch this one again to fully appreciate the diagnosis, great to see it fixed.
Thanks. And I hope you enjoyed the lesson too 🙂
Well done Rick. When you started writing the voltages on the schematic I was fooled to think that the lowside mosfet was somehow shorted. It seems that experience and perseverance always wins over clever newbies like me.
On the other hand the owner reminds me of hundreds of other dudes of the same kind that I met year after year installing audio and lighting systems. They never change.
20:10 - 33:08 This is classic troubleshooting technique from knowing nothing to locating the fault. I’m happy with the way you troubleshoot out loud. Your thinking processes are laid on the table for all to see! I don’t work on amplifiers; but, I can use your techniques to get a better understanding of circuit analysis methods to help me troubleshoot many of the things that hit _my_ bench without schematics! Thank you for showing us such detail from your work! I have learned much from you in the short time I’ve known about your channel and I’ve been doing electronics repair for many years by the seat of my pants!
True, these techniques apply to just about anything you are tring to repair without (or even with) schematics, Thank you 🙂
Great explanation and deduction.
Awesome work on explaining that. I was even able to follow you, not understand everything, but at least follow. I am sure the depth you go into explaining something is annoying to some, but for someone like me it's essential and assists so much more than you imagine. Keep them coming!!
That was a good one from an educational standpoint Rich.
As always another fantastic tutorial. Thank you for sharing your expertise with us. You are a gifted instructor. Hope you revisit your PWM lesson soon. I know you mentioned going into further detail with schematic drawings and such.
This was very cool as your title says if you see something that doesn't make sense read what your meter is saying and think about it. That resistor chain was so obvious. Well done great fix....cheers.
Thank you for sharing your knowledge & findings .. it’s very helpful..
good to see it is finally fixed .... and to use the 3 resistors that is no biggy that will hold for a long time.....
I am so impressed with your abilities to diagnose such an issue, i too will watch this video again, Paul USA
Cheers Paul. This the whole point of repair work, if you take measurements you have to analyse what the results are actually telling you otherwise they won't help you much, This kinda comes down to knowing what you expect before you take the reading and working out what the problem is if the readings don't match your expectations,
Bravo!
I wonder if the resistor is open circuit?
@13:25 Those are some very aggressive lock washers under the screw heads!
Just a quick question about measuring the duty cycle at the mosfets... as you're using your hand held oscilloscope it's obviously fully isolated. I only have my bench oscilloscope which isn't. Can you tell me it this would be a time that it would be necessary to use differential probes given the ground connection to the amp's negative rail? I'm trying to teach myself to repair electronics and obviously don't want to fry my oscilloscope by putting current down the ground connection!
Excellent lesson in diagnosis of the fault and explanation of how the amp actually works.
Thanks!
Thak you very much
timestamp 12:44 on the bad one when you have a higer voltage then the good ones on one side of the resister and no voltage on the other side of the resistor on the bad one ... then the resistor is open as there is no load.... it looks to be a voltage devider so with no voltage the chip can not run
Correct. I laboured the point a bit but that was for educational purposes. it was also worth checking tos ee if a short on the other end of the resistor had caused to to go open (though you may reasonably expect that to cause it to burn up too)
Wow, great job.
Thanks! Very helpful.
Hello, I'm happy to see the FNRSI portable oscillosope at work. 😁
You are lucky becouse that channel is broken, if it was one to the right or left .... . A lot of work must be done.
Thanks for video.
Hi Richard,
I was wondering if you could make a video on understanding net names/signals on boardview software, e.g, I2C, PPV3H, etc. because I don't understand what these mean
Temporary fixes often are the permanent ones 😀😀 nice hob of hunting down to the point of failure
Nice workthrough... Said it'd be a resistor on that bloomin' daughterboard :) Can you try measuring the dead one now it's out of circuit and had some heatsoak from desoldering? Not sure if was just crappy components or dodgy soldering/end caps !
Yeah you did and you were right. Sorry I did measure it out of circuit and it actually read open - but I lost that bit if recording somewhere.
@@LearnElectronicsRepair the 3x10K replacement will be just fine, probably better than the others 😀The one I repaired 10 or so years ago in a similar fashion is still fine as I also didn't have exact SMD parts at the time, I said to myself I'll do the swap for SMD if it ever comes back in for repair again, and so far so good 😉
Was the impedance of the subwoofers this amp drives to make sure there’s not a mismatch that caused the damage to begin with?
Yeah it was, it's 8 ohms. The amp was also tried with another 8 ohm speaker on the bench. Mismatched speaker impedance can damage an amplifier for sure, but it wouldn't cause this sort of failure.
Hi there, another great video from your academy....could you please explain why we measure higher voltage on the output of rectifier (without filtering capacitor) than we measure on the output of AC transformer? Thanks a lot.
You are seeing the higher voltage because of spikes and depending on if there is a load or not on your output the voltage will be higher then the rating.
@@jj74qformerlyjailbreak3 some video for dumb?
If the output of the rectifier is connected to the large smoothing capacitor(s) then the voltage on the transfomer output is the 'average' or rather RMS voltage of the AC voltage and what you read across the output of the nridge rectifier is the peak voltage (Dc) as the capacitors will charge up to peak. So the output of the bridge DC is going to be around 35% higher than the AC voltage coming out of the transformer.
@@LearnElectronicsRepair Thanks, but I was talking about rectifier without filtering capacitor....even then is measured rectified voltage higher than secondary transformer voltage
@@petopeter4832 I don't know the exact reason for that but I suspect you have the same voltage on the output of the rectifier as you do have from the output of the transformer but your multimeter, which is probably 'true RMS' for AC is showing you a different reading to the one it shows you for full wave rectified DC as an artifact of the way the multimeter itself works. You scope would probably show you the same reading (less 2x voltage drop across the silicon rectifiers in the bridge. Take a dual channel scope, use one probe on the output of the transformer and the other probe on the output of the bridge and superimpose the two traces. Make sure you only connect scope ground to one point!
I often just put a "whatever, it's close enough and I have it on hand" component like a resistor while waiting for an order to arrive, because it's so common that it was another part that caused the resistor (or whatever) to blow that half the time I expect the replaced component to immediately blow again. No point in waiting for the perfect/correct part to come in the mail when you can keep diagnosing. I mean, use common sense and don't put a 1/4w resistor in place of a heatsinked wirewound power resistor, but there's nothing wing with parallelling 10 1-ohms together while waiting for that specialty 0.1 ohm to arrive.
😱
So is the scope ground on the negative supply you said? I became worried about the shorting of the supply? I need to think further.... Your previous video somewhere was on the hot side- is that the difference?
Yes, on the negative side. This is chassis ground, not hot ground. In a previous video I proved that this amplifier (and probably all Class D amps) will have a single supply rail, in this case 150V, th-cam.com/video/qpY91f7OqNY/w-d-xo.html
Learned a lot - v helpful, thanks :-)
Good work 👍👍👍
Great job Rick, You will have to frame that resistor and hang it on the wall. (Create a wall of fame haha).
Hehe yeah I should do that 😅
that is why you need hot tweezers then you got that resistor off of there in seconds without damaging anything close to it !!!!!!! ... I keep telling get hot tweezers they are the tools of heaven !!!!
You do. The BC3 tip on the soldering iron also did a pretty good job.
timestamp 31:40 ... and I was right again 🙃
31/30 ha ha the games afoot watson 👍
No, please keep laboring the point.