Some extra info : - The charger identification signal is processed by the EC, then the EC talks to the charger IC through SMBUS to enable charging (battery is involved too). - Lenovo also has a charger identification mechanism. It's of the voltage divider variety (like HP, just reversed). On their cheap consumer laptops (IdeaPad…) there's no protection at all so if the same happens it kills the EC. - The @ symbol with no identifier next to it means means "no stuff", so for example PD2 is not populated. If it was, its role would be to clamp PS_ID between 0 (- diode Vf) to 5V (+diode Vf). @ symbol with an identifier next to it, like PSID, is a BOM option that may or may not be populated. In proper schematics they are listed in the BOM option table. Here PSID is populated of course. - The PSID signal has a 3.3V level, so the TVS diode needs to be specced higher than that, but the lowest possible so that it can avoid too much overvoltage to the rest of the circuit. The "TVN ST523 02 AB0" is rated for up to 5V working voltage. Its breakdown voltage is 6V, and its clamping voltage is up to 13V at 1A or 17V at 7A, so that's a few parameters to take into account when designing the circuit, as well as the capacitance which can limit the speed of the signal it protects.
Ah, maybe the 2-2.5v I had in my head was an average that you'd see if you try to measure it with a DMM... Great info for the specifics, I especially didn't know about @ being a designator for No Stuff.
@@Adamant_IT The transient diode is more likely for ESD protection (static etc). The power from the charger has no trouble destroying it. There should be a current limiting resistor or fuse to protect the diode from continious overvoltage.
especially the lenovos with the square charger and the middle pin,are designed to fail sooner or later and kill your EC.thats what i call planned obsollence.And to think that they could just use a zener diode to protect the middle pin...
Nice job and explanation! I would have measured the second diode and if it survived I would have probably soldered that on (flip it over and press the pins down)
I asked that same question on the badcaps forum. The reply was that the surge usually kills both diodes in the package. Graham demonstrated for us that the body of the SOT523-3 chip was already disintegrating. The schematic makes it look like the diode package is larger than it really is. In reality, SOT523-3 is a very tiny chip.
@@danarepouille1381 I agree, that’s why I said I would have checked if it survived first then probably (depending on how bad it looked under the microscope) solder it on. If you have a strip of new diodes in stock you can go straight to replacing it
Graham, thank you. When I was searching for a video like this a couple years ago, the only ones I could find were not in English. This PD1 TVS diode failure was the reason I bought a hot air station and other tools. There are several discussion threads on the badcaps forum specifically about TVS diodes and the Dell PS_ID circuit.
The first Dell Inspiron that I worked on that had a faulty PS_ID circuit not only had a blown PD1 TVS diode. It also had a blown PQ1 MOSFET. Other folks have reported a blown PR1 33-ohm resistor in this circuit. I was really hoping that either PQ1 or PR1 would have failed on Graham's laptop in this video, to makes things more interesting.
Silly design… there should have been a suitably rated resistor on the signal side of the TVS so that even if the sense line gets shorted to 19V and the TVS conducts, the resistor limits the current so that the TVS doesn’t get blown, which can lead to a chain effect than can cause further stuff to blow, that the TVS was supported to protect.
Nice. My thinkpad x250 has something similar to verify the charger as well. Seen videos on USB-C modding it and you have to add a resistor on the sense pin to trick it into thinking it has a 65w or whatever wattage charger the laptop needs.
Top work as usual and great explanation. Pardon the obvious question but, given that this is a fuse, is there a reason why the diode isn't socketed for easy replacement? Other than cost, of course.
Devices aren't intended to be repaired. But TVS diodes may routinely absorb small transients (static, etc) all the time without actually blowing, they're not a one-shot.
The sense wire also connects to a data component in the charger itself; a Dallas DS2501 EPROM - or similar ( which looks like a 3 pin transistor) which holds the data identifying the charger and it's capacity to the Laptop. I have heard accounts where shorting the 19 v pin to the sense pin can blow the DS2501 as well. How did you know / decide to look at the Laptop sense wire protection rather than the charger DS2501 circuit ??
just tin the injured component with some leaded solder especially if you suspect possible damage on the surface of the pcb ,it goes off without air more often than not.Or if you insist on using the hot air for the removal process,it will be off in a second or two without messing with the resistors and the other important stuff.
TVS Diode Definition: a TVS diode absorbs surge voltage to protect other semiconductor devices, whereas a Zener diode provides constant voltage to other semiconductor devices.
I connected a power supply to the power input on my MSI gaming laptop. I founf the 19v rail and ground. I just wanted to see how much current it would take. And I noted the the current was zero. I the realized that the thin middle pin in the charger was a digital signal. I found schematics online. Is their any way to make the laptop accept input from a power supply other than the original? When I watch the Electronic Repair School on UA-cam he never seems to have any problem to power his laptops with his box of power connectors!
Pro tip: If you install the full version of Acrobat (or some other brand similar software) you can select the guff/text watermark/logo/whatever and press delete to remove it, then re-save the pdf. For a repair vid it looks a lot better without that stuff blocking the view.
Got a build video in the pipeline, but no Windows content planned. My general rule of thumb for windows setups is 'as little as possible'. I try to keep things stock wherever I can, so there's less to change on every setup - so not particularly interesting.
Good fix Graham but also puzzling. That TVS diode is only there to clamp transients, it certainly can’t handle getting a constant 19v on the psid pin. If it hadn’t failed short (rather than open) the next stage would have been taken out too I expect. And after that who knows. It must have been the charger seeing an overcurrent that saved that laptop.
Graham, you could have easily simulated the fault by replacing the blown TVS diode with a wire to ground. Then you could have shown the classic Dell message on the screen "The AC power adapter wattage and type cannot be determined".
An option to save on buying new tweezers is to get a "tweezer sharpener", which is an abrasive with a groove in it (I haven't tried one), or get a set of "red ruby sharpening stones"-they are about 3000 grit-and inpect the tweezer points under a microscope as you get them back into shape. I guess a lot of the price of decent tweezers is the cost of the time for someone to sharpen them. The red ruby stones are really handy for any job that needs a hard, fine abrasive-you can do things like blunting chipped edges of ceramic plates or glass, taking a sharp edge that shouldn't be there off a new tool, that sort of thing, so look for a set with different shapes if you think about getting some.
Exactly the same same thing happened to my Dads laptop, board looks identical in the PD1 area, removed the diode and ordered replacements but never got round to fitting them - probably should or it won't be so easy to repair next time!
2:19 My bro just called Acer * dumb * ☠ somehow that felt personal 😅 💔 kidding aside, yeah its kind of a handy feature that sense pin but at the same time an slight annoyance whenever its a straight up quick repair.
For that motherboard here in North America: PD1 = D5VOL2B3T-7, PQ1 = DMG301NU-7 & PQ2 = MMBT3904-7-F. All three from the manufacturer Diodes Incorporated. Very economical in mouser. All the best. PS: I like Dell too.
Done watching, thank you very much for the informative repair video. I have learned significantly more troubleshooting & repair lessons in this tutorial video and to your other repair videos as well compared to my ENTIRE 4 YEARS OF COLLEGE due to the rotten & outdated standards of education here in the Philippines. I hope you will soon have a mini-series for Schematic & Boardview-free Voltage/Power Rail Tracing[12V/18-20V Main Voltage Rail, 5V, 3.3V, CPU/GPU Core Voltage Rail, DRAM Voltage Rail, IGPU Voltage Rail, System Agent/Northbridge Voltage Rail, PCH Voltage Rail, BIOS Voltage Rail, Battery Power Rail], Proper method of testing/checking of potentially faulty MOSFETs & ICs/Controller Chips, CPU/GPU/PCH Reballing and BIOS Bin File Editing.
Some extra info :
- The charger identification signal is processed by the EC, then the EC talks to the charger IC through SMBUS to enable charging (battery is involved too).
- Lenovo also has a charger identification mechanism. It's of the voltage divider variety (like HP, just reversed). On their cheap consumer laptops (IdeaPad…) there's no protection at all so if the same happens it kills the EC.
- The @ symbol with no identifier next to it means means "no stuff", so for example PD2 is not populated. If it was, its role would be to clamp PS_ID between 0 (- diode Vf) to 5V (+diode Vf). @ symbol with an identifier next to it, like PSID, is a BOM option that may or may not be populated. In proper schematics they are listed in the BOM option table. Here PSID is populated of course.
- The PSID signal has a 3.3V level, so the TVS diode needs to be specced higher than that, but the lowest possible so that it can avoid too much overvoltage to the rest of the circuit. The "TVN ST523 02 AB0" is rated for up to 5V working voltage. Its breakdown voltage is 6V, and its clamping voltage is up to 13V at 1A or 17V at 7A, so that's a few parameters to take into account when designing the circuit, as well as the capacitance which can limit the speed of the signal it protects.
Ah, maybe the 2-2.5v I had in my head was an average that you'd see if you try to measure it with a DMM...
Great info for the specifics, I especially didn't know about @ being a designator for No Stuff.
@@Adamant_IT The transient diode is more likely for ESD protection (static etc).
The power from the charger has no trouble destroying it.
There should be a current limiting resistor or fuse to protect the diode from continious overvoltage.
If Graham had searched the schematic for PS_ID, he would have seen that it goes directly to a pin on the EC chip. On the MEC1416, it is pin 36.
Ironically on Lenovo Legions, it kills the EC anyways, even if the protection is there
especially the lenovos with the square charger and the middle pin,are designed to fail sooner or later and kill your EC.thats what i call planned obsollence.And to think that they could just use a zener diode to protect the middle pin...
I think you could just use the other side of the broken diode, it should be the same value !!!
Glad you did post this as a video even if we missed the real time diagnosis. The explanation was totally worth it.
Nice job and explanation! I would have measured the second diode and if it survived I would have probably soldered that on (flip it over and press the pins down)
I asked that same question on the badcaps forum. The reply was that the surge usually kills both diodes in the package. Graham demonstrated for us that the body of the SOT523-3 chip was already disintegrating. The schematic makes it look like the diode package is larger than it really is. In reality, SOT523-3 is a very tiny chip.
@@danarepouille1381 I agree, that’s why I said I would have checked if it survived first then probably (depending on how bad it looked under the microscope) solder it on. If you have a strip of new diodes in stock you can go straight to replacing it
@@electrorep3 I did wonder why Graham did not bother to test the other side of the diode package, just out of curiosity.
Thanks for another enjoyable video.
Graham, thank you. When I was searching for a video like this a couple years ago, the only ones I could find were not in English. This PD1 TVS diode failure was the reason I bought a hot air station and other tools. There are several discussion threads on the badcaps forum specifically about TVS diodes and the Dell PS_ID circuit.
Dell are not idiots? I would do a friendly debate with you on that sometime. Cheers, thanks for a good video.
The first Dell Inspiron that I worked on that had a faulty PS_ID circuit not only had a blown PD1 TVS diode. It also had a blown PQ1 MOSFET. Other folks have reported a blown PR1 33-ohm resistor in this circuit. I was really hoping that either PQ1 or PR1 would have failed on Graham's laptop in this video, to makes things more interesting.
Silly design… there should have been a suitably rated resistor on the signal side of the TVS so that even if the sense line gets shorted to 19V and the TVS conducts, the resistor limits the current so that the TVS doesn’t get blown, which can lead to a chain effect than can cause further stuff to blow, that the TVS was supported to protect.
Nice. My thinkpad x250 has something similar to verify the charger as well. Seen videos on USB-C modding it and you have to add a resistor on the sense pin to trick it into thinking it has a 65w or whatever wattage charger the laptop needs.
out of curiosity, did you check if the unused diode in that dual-diode package PD1 (miraculously) survived? :P
Top work as usual and great explanation. Pardon the obvious question but, given that this is a fuse, is there a reason why the diode isn't socketed for easy replacement? Other than cost, of course.
Devices aren't intended to be repaired. But TVS diodes may routinely absorb small transients (static, etc) all the time without actually blowing, they're not a one-shot.
Very well explained how the circuit works
The sense wire also connects to a data component in the charger itself; a Dallas DS2501 EPROM - or similar ( which looks like a 3 pin transistor) which holds the data identifying the charger and it's capacity to the Laptop. I have heard accounts where shorting the 19 v pin to the sense pin can blow the DS2501 as well. How did you know / decide to look at the Laptop sense wire protection rather than the charger DS2501 circuit ??
It protected the circuit for what, Dell will just ask to replace the board, so it protected the circuit for dumpyard.
just tin the injured component with some leaded solder especially if you suspect possible damage on the surface of the pcb ,it goes off without air more often than not.Or if you insist on using the hot air for the removal process,it will be off in a second or two without messing with the resistors and the other important stuff.
Very thanks!, I always learn from your videos😊
This is great just had the same issue with an Inspiron in the workshop, different MB with dedicated graphics but PD1 large hole.
That is why I don't buy any laptop that wants original charger by identification.
Thanks a lot, Graham.
Thank you for a very informative video for the neanderthals amongst us (yes that's me).
TVS Diode Definition: a TVS diode absorbs surge voltage to protect other semiconductor devices, whereas a Zener diode provides constant voltage to other semiconductor devices.
The difference is context. A TVS diode is a type of zener with specific characteristics. That's why the circuit symbol is the same.
I have a Lenovo here that stopped charging, now the charger and the mainboard are dead, unfortunately no smoking guns.
I connected a power supply to the power input on my MSI gaming laptop. I founf the 19v rail and ground. I just wanted to see how much current it would take. And I noted the the current was zero. I the realized that the thin middle pin in the charger was a digital signal. I found schematics online. Is their any way to make the laptop accept input from a power supply other than the original? When I watch the Electronic Repair School on UA-cam he never seems to have any problem to power his laptops with his box of power connectors!
Pretty sure Lenovos with the squareish yellow charge connectors also have a data pin in the centre so probably have similar protection
Another over engineered protection circuit that does't work well.
When all that was needed was 1k resistor and 5v zener diode.
See, if this was a Lenovo, the SIO would be cooked.
Ask me how I know...
Thank you, btw you could have used the other diode in the double diode, probably this was not burned😅
The brave little tailor knows it all...
These laptops are designed and built by Compal, and they do know how to build a laptop to a budget
Pro tip: If you install the full version of Acrobat (or some other brand similar software) you can select the guff/text watermark/logo/whatever and press delete to remove it, then re-save the pdf. For a repair vid it looks a lot better without that stuff blocking the view.
good info. thanks.
Another great fix mate nice one.
Very nice info again thnx.
Great lesson ❤
Great video.
Good Stuff!🍻
great instruction
Any PC building video's coming? I really like those video's and I would like to see the way that you configure windows 11 the way you like.
Got a build video in the pipeline, but no Windows content planned. My general rule of thumb for windows setups is 'as little as possible'. I try to keep things stock wherever I can, so there's less to change on every setup - so not particularly interesting.
Good fix Graham but also puzzling.
That TVS diode is only there to clamp transients, it certainly can’t handle getting a constant 19v on the psid pin.
If it hadn’t failed short (rather than open) the next stage would have been taken out too I expect. And after that who knows.
It must have been the charger seeing an overcurrent that saved that laptop.
The next stage disconnects when >5V DC or so is present on the line, so theoretically protects everything down the line.
👍
Graham, you could have easily simulated the fault by replacing the blown TVS diode with a wire to ground. Then you could have shown the classic Dell message on the screen "The AC power adapter wattage and type cannot be determined".
An option to save on buying new tweezers is to get a "tweezer sharpener", which is an abrasive with a groove in it (I haven't tried one), or get a set of "red ruby sharpening stones"-they are about 3000 grit-and inpect the tweezer points under a microscope as you get them back into shape. I guess a lot of the price of decent tweezers is the cost of the time for someone to sharpen them. The red ruby stones are really handy for any job that needs a hard, fine abrasive-you can do things like blunting chipped edges of ceramic plates or glass, taking a sharp edge that shouldn't be there off a new tool, that sort of thing, so look for a set with different shapes if you think about getting some.
Exactly the same same thing happened to my Dads laptop, board looks identical in the PD1 area, removed the diode and ordered replacements but never got round to fitting them - probably should or it won't be so easy to repair next time!
2:19 My bro just called Acer * dumb * ☠ somehow that felt personal 😅 💔
kidding aside, yeah its kind of a handy feature that sense pin but at the same time an slight annoyance whenever its a straight up quick repair.
I guess both of us could use a haircut...
Great Lesson. Thank you.
Do you ever worry that the hot air will soften the tips of your tweezers? Thanks for all your videos. Great work.
Naa, nowhere near hot enough to do that.
For that motherboard here in North America: PD1 = D5VOL2B3T-7, PQ1 = DMG301NU-7 & PQ2 = MMBT3904-7-F. All three from the manufacturer Diodes Incorporated. Very economical in mouser. All the best.
PS: I like Dell too.
Done watching, thank you very much for the informative repair video. I have learned significantly more troubleshooting & repair lessons in this tutorial video and to your other repair videos as well compared to my ENTIRE 4 YEARS OF COLLEGE due to the rotten & outdated standards of education here in the Philippines. I hope you will soon have a mini-series for Schematic & Boardview-free Voltage/Power Rail Tracing[12V/18-20V Main Voltage Rail, 5V, 3.3V, CPU/GPU Core Voltage Rail, DRAM Voltage Rail, IGPU Voltage Rail, System Agent/Northbridge Voltage Rail, PCH Voltage Rail, BIOS Voltage Rail, Battery Power Rail], Proper method of testing/checking of potentially faulty MOSFETs & ICs/Controller Chips, CPU/GPU/PCH Reballing and BIOS Bin File Editing.