@Learn Electronic Repair I wanted to say Thank YOU! for all the very informative videos you've blessed us with, especially the GPU specific ones. You've more than earned a life long subscriber here. You've inspired me, more than i can relay without getting all sentiMENTAL here LOLL. Thank you, sir.
Hey Rich, another top video! Just wanted to take time out and thank you for consistently putting out such great material. I started watching your channel a couple years ago as it would help in my day to day work as a systems technician within the medical robotics field. Fast forward two years, and I'm now being put through university by my employer to become an engineer (something I could've never imagined happening). I firmly believe this is in large part to the knowledge I've gained from watching the content you've put out. Again I just wanted to say thank you, watching and learning electronics with you has been great fun and has helped to change my life. Stay safe, and I'll be waiting eagerly for the update to this mini series! Cheers
Given the lack of a schematic, I thought you might have traced that issue progressively backwards from the protection mode light to find out what component/s provide it with power and why/how.
That is another way. I think starting by checking for voltage rails then referring to the amplifier IC datasheets was a reasonable way too. There is no right way or wrong way IMHO
@LearnElectronicsRepair yes! But that may be not clear to everybody. Finding faults in equipment without schematic is sometimes very hard. Right now I am chasing a no camshaft sensor signal in a 2002 Lupo. I even opened the ecu to trace the signals to the ecu print. It appears to be corroded ecu connector: I connected the ecu print without the housing and the error is gone.... cheers!!
Had me up half the night watching. Would be very interested to see the result of switching the chips. I’d have looked for a fault on the thermal sensor because that’s what I’ve been told goes on some hk gear, but I’d still have no idea what I was looking for… perhaps a little better informed after watching your vids
At some point you have to lean back and wonder if you can fix it. Been there, tried it, several times. You need to do something entirely different for a couple of days, then return to the problem. Then I'd start by tracing the fault lamp backwards and try figure out which circuit turns on the lamp. Then take it from there. Guarantee this will lead you on a new track.
Hi Richard, love your content and the way you explain things. I have a problem with a power supply. I accidentally shorted the positive of bridge recifier to a heatsink while testing voltages. Obviously went bang. Now every time i plug it in there is a 400v 4.7uf capacitor that explodes and a diode that shorts thru. I cant for the life of me work out why this is now happening. The cap is by itself after 2 big 200v 470uf caps. Basically the trace comes from the positive side of BR and into the diode and 400v cap. It does branch of to a triac and 2 mosfets also. Any advice would be very much appreciated. Thank you for all you do.
Nice job Richard. Interesting find. It's like 2 separate diodes have shorted internally in series or something. Creating a double diode reading of 1.2 vs .6 weird! I wonder if you just remove the chip, would the unit start up.
Hi, good and lenghty / informative video thank you for your great patience. However, before ending the video I personally woud have unsoldered the op amp and power up the unit to see it the protection light is back to normal before deciding to oder the cip. Another way in my opinion would have been to look to see you might have had another type of op amp ( any other quad op amp) that has the same pinout and takes the same voltages just to try to see if the unit wants to come back to life and then....order the proper cip. my 2 cent.
LM13700 is not a quad op amp it is a rather specialised dual opamp. Removing the IC would not necessarily cause the protect LEN to go green, in fact I very much doubt that is what would happen, it most likely needs the opamp to be functioning to do that.. But there are various ways to tackle this sort of repair, and in this case checking the inverting and non inverting inputs in reverse polarity diode mode is a good test. All(?) opamps and many other chips will have clamping diodes to prevent the input going below the negative supply rail and this is exactly what I am checking here. If the diodes are blown we can say the chip is toast. No question about that 😉
Hi Richard from Sydney Australia. In relation to the electrical activity of the chip pins SOIC. When applying power in the board intially, would isopropyl alcohol spray evaporate slower/ faster as an indicator of a chip fault. Secondly would a "hot chip' show using infa red camera? (Just spit balling) Thankyou for showing how to order chips online and pay with credit card. ◾🛐
Haha, I did the order bit just to show the parts were cheap enough, and that I was going to continue with the repair. Whether the likely faulty LM13700 dual op amp would also show up on the thermal camera or not I don't know, sorry I could have quickly tested that, but at that point I felt I had seen enough evidence to tell me there is something wrong with that chip, and from what I had already figured out about how protect mode works on this speaker it is in about the right place on the PCB to be involved. 😉
At 24:43 you wonder why the standby signal is sent up the ribbon cable... I think you've already seen why... it's to drive the red/green standby indicator. Fingers crossed the faulty chip you found fixes the issue... I await the next part with bated breath ;-)
Wow! the LM3700 is an impressive chip indeed for audio work. there are application notes from simple amps to VCOs and super accurate stereo volume controls. I would love to know what this setup is using them for...cheers.
I think it maybe a red herring, it looks like nothing is connected to the suspected faulty inputs. You could try swapping the chips round and compare measurements again or see if the unit behaves differently when powered on!
Yes but no but - 1. the reverse biased diodes I am looking for are in the op amp itself and they are not there which tells me damaged chip. 2. No circuit designer in their right mind leaves unused inputs to an opamp floating, therefore they connect to the other side of the PCB or to an internal layer through Vias. The opamp still tests as faulty anyway. I don't have any replacements here so had no reasonable option other that to order some
@@LearnElectronicsRepair well I don't disagree, but I'm not convinced - all seems too easy 🤣 Upon further research, with this specific opamp pins 2, 3, 4, 5 can be left floating, you just need to connect pin 1 to V-
@@Sydney268 All(?) op amps will have internal clamping diodes to prevent the inputs going below the negative supply rail. This is what I am looking for with the reverse polarity diode mode test I used. If the clamping diodes are blown/faulty then we can say the IC is toast. This will be true whether the inputs are actually used or not. The same is true for most logic IC as well.
If you haven’t ascertained whether the fault is an open or a short( if you have and i missed it, disregard), can you start with thermal imaging to see if there’s a hot spot caused by a short to power or short to ground?
From what I can see (which is only so much given the lack of schematics etc) is that the protection features of the TDA8954 Amplifier ICs are being used of course, because I don't see how you could disable them anyway, but the DIAG1 and DIAG2 pins are not being monitored by the rest of the circuit. This does not stop the internal protection from working of course. Then there appears to be some external circuitry, and one would of course expect that to use op amps, which also monitors some conditions and holds the amplifiers in standby using the MODE pin, until it is happy they can start. This circuit controls the Protect LED on the mixer panel. Some of that circuitry will control features like auto shut down with no audio after 2 hours that is mentioned in the user manual. There is a switch to disable this feature and it is disabled. This is 'probably' what the CD4536 timer IC is doing. Then other parts of the circuit will implement the Standby switch which is also on the mixer panel. So that's what it looks like we have here. I can see some very odd looking readings around one of the LM13700 dual op amps, specifically pins 3 and 4 are +/- inputs to one of the two opamps it contains and it just looks 'wrong' to me compared to the other three (two in each package). This is based partly on knowing how to quickly go/no go test op amps in circuit and partly on experience of electronics repair in general. What I don't have is any prior or specialist knowledge of these speaker systems. What I can say is that area of the PCB around the various opamps will certainly be involved in the protection mode LED, amongst other things. So my best guess based on the measurements I took as a whole, and it is just a 'best guess', is we have a fault in the protection monitor circuit itself, not actually a fault on a power rail or DC offset at the speaker terminals. What I generally call a 'phantom fault'. Of course using the thermal camera won't hurt and may help even if it just confirms what I already think. And it wouldn't be the first time I was proven wrong either and had to rethink the whole thing 😉
@@LearnElectronicsRepair It might be an interesting exercise to add pullups to the DIAG pins - to 5V of course and see what the chip itself is doing - even after fixing it. It's an interesting way to expose the internal protection features of the chip and the experience could be useful for when you (we!) come across circuits that do make use of them. Personally I would have swapped those two op-amps (are they the same??) but that's just me :-). It's nice way to check the circuit though, a useful technique.
Hello. I have pcb from a mercedes viano, door controller unit. They are quoting £2000 for a new one. Any chance I can pay you to look at it? It had a visual water damage in the lower section- cleaned it away with isopropanol, and tried but no luck. I have resistance through most of the board, but my electronic knowledge isn’t that good🙂
40:17 -- Many years ago I went to the Canary Islands and did not find a canary. Then I went to the Virgin Islands and couldn't find anything there either. Then a neighbor went to a local pet shop and said to the store keeper: " I want a canary that;s a good singer ' The store keeper brought back a small box - saying - " Inside is a a canary that is an excellent singer " So the buyer took the canary in the box and brought him home -- letting him into the cage - only to discover that the canary had only one leg. Becoming upset at this swindle - the following day - he took the canary back to the pet store and confronted the owner ; "" This canary has only one leg "" he said. To which the Store Keeper replied" "" You said that you wanted a good singer - you did not say that you wanted a dancer ""
@@JonnyMac351 Yes Exactly 🙂. They are there to prevent the inputs going below the negative supply rail. This is why I do a reverse polarity diode mode test
I have an active speaker which has a dc offset on the tweeter output of -23 volts, it obviously burns the tweeter out but also the IRF530N supplying it, I can't figure it out, I'm leaving it to one side now with an amplifier until I have learned more and have a better understanding! gone through 2 tweeters and 5 fets now 😒
@@LearnElectronicsRepair I was about to comment this on the first video . The light bulb went on and you switched it onto direct anyways, which I found strange. I have an ATX power supply. The light bulb only detects the "short circuit" when output current increases beyond a value. In lower currents (higher resistance on the load) it runs just fine. I suspected something wrong with the sense system of the PFC, since the PWM IC seems fine to me.
So I bypassed the light bulb and... nothing happened. The PSU works just fine. And I thinking there was some weird failure somewhere... But live and learn. Took the hint from the previous video, where Richard mentions that since the fuse didn't burn, it should be ok to bypass the light bulb. This ATX is a small one, with lots of smd in the PWM and PFC control signal circuits. So it was fun to work with, as least. :P
@@LearnElectronicsRepair you could have pulled the part off the board and tested it. I don't know how logical that is, but it's possible. Getting parts off ali it might be smart to test those before you try to fit them. They could be anything really. What they're most likely not is authentic. But at least make sure they're functional.
You don't suppose one of the main amplifiers could be shot do you? I hope you're right about the op amp. It seems like a nice unit. You do get a lot of that sort of equipment. The Island must be Party Central.
The honest answer is, I don't really know. With this sort of repair you just keep going until you find something obviously wrong, which in this case I did, but it is always a kinda mystery you just have to apply what you know and try to fix it
Regards Party Central, check out some of our videos on Gran Canaria Uncovered channel Here's a good example th-cam.com/video/nxtUY5GtgOQ/w-d-xo.html especially from 04:30 onwards
Hi Richard 🤗 One question, ähhh.. or more🤣 From what,trough is the indicator led driven ?? What is the reason part?. I mean not the reason. Go back one by one. Who is the fault detector?? Did you meassure the output stage from the audio power ic's to plus or minus ??(remember the voltage converter, high side , low side mosfet's ) The D amplifier work like a psu but the other way around. The output signal looks like a AM modulation.
![ลองสุ่มไอโฟน 990 โกงมั้ย? [ โกงมั้ยครับ ep.101 ] | DOM](http://i.ytimg.com/vi/bfsWe0j492k/mqdefault.jpg)
@Learn Electronic Repair I wanted to say Thank YOU! for all the very informative videos you've blessed us with, especially the GPU specific ones. You've more than earned a life long subscriber here. You've inspired me, more than i can relay without getting all sentiMENTAL here LOLL. Thank you, sir.
Hey Rich, another top video! Just wanted to take time out and thank you for consistently putting out such great material. I started watching your channel a couple years ago as it would help in my day to day work as a systems technician within the medical robotics field. Fast forward two years, and I'm now being put through university by my employer to become an engineer (something I could've never imagined happening). I firmly believe this is in large part to the knowledge I've gained from watching the content you've put out. Again I just wanted to say thank you, watching and learning electronics with you has been great fun and has helped to change my life. Stay safe, and I'll be waiting eagerly for the update to this mini series! Cheers
Thank you. You made me blush 🤭 But thank you anyway 😁
Heya, I hope your right that would be amazing can't wait till the parts arrive
Given the lack of a schematic, I thought you might have traced that issue progressively backwards from the protection mode light to find out what component/s provide it with power and why/how.
That is another way. I think starting by checking for voltage rails then referring to the amplifier IC datasheets was a reasonable way too. There is no right way or wrong way IMHO
@@LearnElectronicsRepairyou have to somehow eliminate possible causes to end up with the root cause.
@@therealspixycat Isn't that basically what I did? 😉
@LearnElectronicsRepair yes! But that may be not clear to everybody. Finding faults in equipment without schematic is sometimes very hard. Right now I am chasing a no camshaft sensor signal in a 2002 Lupo. I even opened the ecu to trace the signals to the ecu print. It appears to be corroded ecu connector: I connected the ecu print without the housing and the error is gone.... cheers!!
Had me up half the night watching.
Would be very interested to see the result of switching the chips.
I’d have looked for a fault on the thermal sensor because that’s what I’ve been told goes on some hk gear, but I’d still have no idea what I was looking for… perhaps a little better informed after watching your vids
At some point you have to lean back and wonder if you can fix it.
Been there, tried it, several times.
You need to do something entirely different for a couple of days, then return to the problem.
Then I'd start by tracing the fault lamp backwards and try figure out which circuit turns on the lamp.
Then take it from there.
Guarantee this will lead you on a new track.
Yes that also works for me sometimes. Put it down for a while and you may get some inspiration
Hi Richard, love your content and the way you explain things. I have a problem with a power supply. I accidentally shorted the positive of bridge recifier to a heatsink while testing voltages. Obviously went bang. Now every time i plug it in there is a 400v 4.7uf capacitor that explodes and a diode that shorts thru. I cant for the life of me work out why this is now happening. The cap is by itself after 2 big 200v 470uf caps. Basically the trace comes from the positive side of BR and into the diode and 400v cap. It does branch of to a triac and 2 mosfets also. Any advice would be very much appreciated. Thank you for all you do.
Nice job Richard. Interesting find. It's like 2 separate diodes have shorted internally in series or something. Creating a double diode reading of 1.2 vs .6 weird! I wonder if you just remove the chip, would the unit start up.
10:47 Hi Rich, I'm wondering why you soldered on this random resistor, which you did in episode 1. Cheers Darren
Hi, good and lenghty / informative video thank you for your great patience. However, before ending the video I personally woud have unsoldered the op amp and power up the unit to see it the protection light is back to normal before deciding to oder the cip. Another way in my opinion would have been to look to see you might have had another type of op amp ( any other quad op amp) that has the same pinout and takes the same voltages just to try to see if the unit wants to come back to life and then....order the proper cip. my 2 cent.
LM13700 is not a quad op amp it is a rather specialised dual opamp. Removing the IC would not necessarily cause the protect LEN to go green, in fact I very much doubt that is what would happen, it most likely needs the opamp to be functioning to do that.. But there are various ways to tackle this sort of repair, and in this case checking the inverting and non inverting inputs in reverse polarity diode mode is a good test. All(?) opamps and many other chips will have clamping diodes to prevent the input going below the negative supply rail and this is exactly what I am checking here. If the diodes are blown we can say the chip is toast. No question about that 😉
Hi Richard from Sydney Australia.
In relation to the electrical activity of the chip pins SOIC. When applying power in the board intially, would isopropyl alcohol spray evaporate slower/ faster as an indicator of a chip fault. Secondly would a "hot chip' show using infa red camera? (Just spit balling) Thankyou for showing how to order chips online and pay with credit card.
◾🛐
Haha, I did the order bit just to show the parts were cheap enough, and that I was going to continue with the repair. Whether the likely faulty LM13700 dual op amp would also show up on the thermal camera or not I don't know, sorry I could have quickly tested that, but at that point I felt I had seen enough evidence to tell me there is something wrong with that chip, and from what I had already figured out about how protect mode works on this speaker it is in about the right place on the PCB to be involved. 😉
At 24:43 you wonder why the standby signal is sent up the ribbon cable... I think you've already seen why... it's to drive the red/green standby indicator.
Fingers crossed the faulty chip you found fixes the issue... I await the next part with bated breath ;-)
Another great, egde of the seat video!
Looks like youre onto a winner here🙂
Wow! the LM3700 is an impressive chip indeed for audio work. there are application notes from simple amps to VCOs and super accurate stereo volume controls. I would love to know what this setup is using them for...cheers.
LM13700
Yeah, my bad! same OTA and still a fascinating chip cheers!@@LearnElectronicsRepair
W❤W! That’s Tremendously Awesome! Have A Great Weekend! 🤗❤️✨
Would this be a good case for testing around the op amps with something like the Huntron Tracker?
I think it maybe a red herring, it looks like nothing is connected to the suspected faulty inputs. You could try swapping the chips round and compare measurements again or see if the unit behaves differently when powered on!
Yes but no but - 1. the reverse biased diodes I am looking for are in the op amp itself and they are not there which tells me damaged chip. 2. No circuit designer in their right mind leaves unused inputs to an opamp floating, therefore they connect to the other side of the PCB or to an internal layer through Vias. The opamp still tests as faulty anyway. I don't have any replacements here so had no reasonable option other that to order some
@@LearnElectronicsRepair well I don't disagree, but I'm not convinced - all seems too easy 🤣 Upon further research, with this specific opamp pins 2, 3, 4, 5 can be left floating, you just need to connect pin 1 to V-
@@Sydney268 All(?) op amps will have internal clamping diodes to prevent the inputs going below the negative supply rail. This is what I am looking for with the reverse polarity diode mode test I used. If the clamping diodes are blown/faulty then we can say the IC is toast. This will be true whether the inputs are actually used or not. The same is true for most logic IC as well.
If you haven’t ascertained whether the fault is an open or a short( if you have and i missed it, disregard), can you start with thermal imaging to see if there’s a hot spot caused by a short to power or short to ground?
From what I can see (which is only so much given the lack of schematics etc) is that the protection features of the TDA8954 Amplifier ICs are being used of course, because I don't see how you could disable them anyway, but the DIAG1 and DIAG2 pins are not being monitored by the rest of the circuit. This does not stop the internal protection from working of course.
Then there appears to be some external circuitry, and one would of course expect that to use op amps, which also monitors some conditions and holds the amplifiers in standby using the MODE pin, until it is happy they can start. This circuit controls the Protect LED on the mixer panel. Some of that circuitry will control features like auto shut down with no audio after 2 hours that is mentioned in the user manual. There is a switch to disable this feature and it is disabled. This is 'probably' what the CD4536 timer IC is doing. Then other parts of the circuit will implement the Standby switch which is also on the mixer panel.
So that's what it looks like we have here. I can see some very odd looking readings around one of the LM13700 dual op amps, specifically pins 3 and 4 are +/- inputs to one of the two opamps it contains and it just looks 'wrong' to me compared to the other three (two in each package). This is based partly on knowing how to quickly go/no go test op amps in circuit and partly on experience of electronics repair in general. What I don't have is any prior or specialist knowledge of these speaker systems. What I can say is that area of the PCB around the various opamps will certainly be involved in the protection mode LED, amongst other things.
So my best guess based on the measurements I took as a whole, and it is just a 'best guess', is we have a fault in the protection monitor circuit itself, not actually a fault on a power rail or DC offset at the speaker terminals. What I generally call a 'phantom fault'. Of course using the thermal camera won't hurt and may help even if it just confirms what I already think. And it wouldn't be the first time I was proven wrong either and had to rethink the whole thing 😉
@@LearnElectronicsRepair It might be an interesting exercise to add pullups to the DIAG pins - to 5V of course and see what the chip itself is doing - even after fixing it. It's an interesting way to expose the internal protection features of the chip and the experience could be useful for when you (we!) come across circuits that do make use of them.
Personally I would have swapped those two op-amps (are they the same??) but that's just me :-). It's nice way to check the circuit though, a useful technique.
Maybe if you connect a diode to sub you can bypass mute unmute and basicly disable it
Hello.
I have pcb from a mercedes viano, door controller unit. They are quoting £2000 for a new one.
Any chance I can pay you to look at it?
It had a visual water damage in the lower section- cleaned it away with isopropanol, and tried but no luck.
I have resistance through most of the board, but my electronic knowledge isn’t that good🙂
Do you ever use thermal imaging in your diagnosis?
Yes, quite often
@LearnElectronicsRepair that's great..I need to look through your video catalogue and see. Wonderfully concise, you are. Cheers from 🇦🇺
40:17 --
Many years ago I went to the Canary Islands
and did not find a canary.
Then I went to the Virgin Islands and couldn't
find anything there either.
Then a neighbor went to a local pet shop
and said to the store keeper:
" I want a canary that;s a good singer '
The store keeper brought back a small box - saying -
" Inside is a a canary that is an excellent singer "
So the buyer took the canary in the box and brought
him home -- letting him into the cage - only to discover
that the canary had only one leg.
Becoming upset at this swindle - the following day -
he took the canary back to the pet store and confronted
the owner ;
"" This canary has only one leg "" he said.
To which the Store Keeper replied"
"" You said that you wanted a good singer - you did
not say that you wanted a dancer ""
Blimey your videos are good
hi richard from algeria , i think its not connected to other circuits this is why it made different readings .
The diodes are internal with those op amps so they should always read as a diode.
@@JonnyMac351 Yes Exactly 🙂. They are there to prevent the inputs going below the negative supply rail. This is why I do a reverse polarity diode mode test
Lift those mode pin one by one maybe one of those chips is pulling it down
That is a possibility 🙂
I fixed a monitor without any schematic, just used oscilloscope and changed one transistor.
Isn't protection most often activated when a short is detected on the output?
That, and if there is a DC offset at the output
I have an active speaker which has a dc offset on the tweeter output of -23 volts, it obviously burns the tweeter out but also the IRF530N supplying it, I can't figure it out, I'm leaving it to one side now with an amplifier until I have learned more and have a better understanding! gone through 2 tweeters and 5 fets now 😒
@@LearnElectronicsRepair I was about to comment this on the first video . The light bulb went on and you switched it onto direct anyways, which I found strange.
I have an ATX power supply. The light bulb only detects the "short circuit" when output current increases beyond a value. In lower currents (higher resistance on the load) it runs just fine.
I suspected something wrong with the sense system of the PFC, since the PWM IC seems fine to me.
So I bypassed the light bulb and... nothing happened. The PSU works just fine. And I thinking there was some weird failure somewhere... But live and learn.
Took the hint from the previous video, where Richard mentions that since the fuse didn't burn, it should be ok to bypass the light bulb.
This ATX is a small one, with lots of smd in the PWM and PFC control signal circuits. So it was fun to work with, as least. :P
Maybe the chip is bad but what killed it? You could put another one in and it could meet the same fate.
Agreed but I have no way without schematics to prove this one way or the other. Therefore the only logical option is to replace it,
@@LearnElectronicsRepair you could have pulled the part off the board and tested it. I don't know how logical that is, but it's possible. Getting parts off ali it might be smart to test those before you try to fit them. They could be anything really. What they're most likely not is authentic. But at least make sure they're functional.
@@1pcfred The diode mode test in reverse polarity proves the IC is faulty, no need to test it more.
You don't suppose one of the main amplifiers could be shot do you? I hope you're right about the op amp. It seems like a nice unit.
You do get a lot of that sort of equipment. The Island must be Party Central.
The honest answer is, I don't really know. With this sort of repair you just keep going until you find something obviously wrong, which in this case I did, but it is always a kinda mystery you just have to apply what you know and try to fix it
Regards Party Central, check out some of our videos on Gran Canaria Uncovered channel
Here's a good example th-cam.com/video/nxtUY5GtgOQ/w-d-xo.html especially from 04:30 onwards
Is it faulty or is it being used wrong, the customer has forgot to do something?
Hi Richard 🤗
One question, ähhh.. or more🤣
From what,trough is the indicator led driven ?? What is the reason part?. I mean not the reason. Go back one by one. Who is the fault detector??
Did you meassure the output stage from the audio power ic's to plus or minus ??(remember the voltage converter, high side , low side mosfet's )
The D amplifier work like a psu but the other way around. The output signal looks like a AM modulation.
I checked for any DC offset on the power amp outputs in part one. This would be same as looking for shorts to either power rail yes?