How to check voltage level at a resistor?

[Renate]

Swinging logic sounds like fun.

It is!

Wow, you've given me a load.

In most modern SoC (system on chip) you're got a couple of hundred pins or contacts
Connections are at a premium so you want to keep that number down.
But a chip is expensive to design and it might get used for lots of different usages.
Somebody might want a LCD display with a good 20 pins. Somebody might have no need of a display.
So what you have is that any modern SoC has a "Pin Mux".
Usually that means that every single pin can be a GPIO. Some of these pins could be UARTs. Some of them could be I²C.
Let's say that you need a UART. There could be 6 UARTs built into the SoC.
You look at the documentation (hard to find sometimes) for your chip.
"Well, what if I take UART1? I can assign that to pins 25/26 or 90/91 or 124/125. Oh, wait, I'm already using pin 26 to drive the charging LED and 90 is part of my SD card interface and I've got the keyboard connected in the 125 group. Guess I'll use UART2 instead. Of the 4 possibilities for that pins 62/63 are entirely clear."
So the Pin Mux is like a switchboard for connecting functional units inside the chips to pins that connect to the output.
Unfortunately, switchboards are very expensive (in terms of silicon real estate) so we don't make it that you can connect anything to any pin.
But hopefully they give you enough possibilities that you don't get too wedged designing things.

Another job of the Pin Mux (really the Pin Pad configuration) is to set whether a pin is an input/output/both, how hard it drives an output, whether an input has resistors to pull it up or down and for some chips whether the pin works on 1.8V or 3.3V logic levels.

As far as test points go. Most circuit boards have tiny gold dots that allow for connection for testing.
For instance, you want to be able to test if the board will power on without the little button board for the power switch connected.
So they put a little dot that can be probed by a "nail" or "pogo pin", a spring-loaded contact.
You'll probably see a group of three of them around the VolUp/VolDn/Power.

The power button has to wake the device from full off, so it may be wired differently than buttons that only have to work when it's on.

You're telling me that you're measuring 3.7V on a resistor that goes to the power button?
That seems to be the full LiPo voltage. When you press the power button you see no difference in the voltage from either end of the resistor to ground?
If you can, take a good high-res photo of the area right there.

Most modern Androids do OTG just fine (with an OTG adapter).
There can be problems if the peripheral is looking to be supplied with too much current.
You can use a hub on OTG. The "input" goes to the OTG adapter, one of the "outputs" goes to the peripheral.

 

[Rizzi87]

I know. That's a chip-off procedure. But that doesn't work on devices running Android 6 and above because of hardware based encryption of storage chips. This is enforced by Google. Manufacturers must comply with Google's demands if they want to receive Android certification.

Thanks. I wasn't aware of this fact so it's a nice way to learn on the fly.

I'm sorry to hear. I know the feeling.

Yeah mate. It's almost similar to a heartbreak

That's a good indication of a short. Problem is in knowing your reference points. How much is too much? Similar to voltage, how high temperature is too high? How low temperature is too low? If you don't have a reference, it doesn't tell you much. Unless it's in the extreme. Extremely low, or extremely high. Reference point for that might be if you get a burn mark if you touch it or a frost bite. But in general, abnormal temperature is a good indication of a short circuit. If you can rule out overheating.

The difference in the temps of the area that gets heated versus the rest of the board is apparently enough to realise that it's not normal. I have found 2 capacitors near the processor that are not giving out any readings in either direction.

What equipment is that? What components have you tested if you have not removed the shields yet?

The manual mentions some kinda jig that Samsung service tech uses for diagnostics and repairs. Also to measure the frequency of the oscillator, one needs an oscilloscope which I do not have access to currently.

I have been referencing the boardview in the manual and checking the resistors, diodes and capacitors all over the board. The caveat here is I do not know which components are to be tested in forward bias or otherwise (i.e. red probe on ground vs. black probe on ground). Moreover, I'm yet to learn how to measure/test SMD inductors so as to find out any possible shorting of those components.

EMI shields? Is that what those things are called? I hate those. They are troublesome to remove. Some of them have a top cover that can be lifted and put back on, others don't. I knocked off a tiny capacitor on one of my test boards while removing the shield with pliers (expensive precision pliers for electronics by Knipex, "Made in Germany"). That board took a turn for the worse because of it. But I have saved the tiny capacitor. Good thing is I saw it and didn't digest it or something, it's almost invisible, it's like 1 mm x 0.5 mm.

Yeah, I reckon that's what they are called from the tutorials/guides I have been perusing.
I get what you are saying with 'invisible' capacitor. I realised about some of those being on the board only after zooming in on some macro pics I'd taken of the mobo!

Does it have power? The first thing you should get in terms of equipment is a USB power meter.

Yes it has power. I see the menu and back keys light up in addition to the service/charging led and vibration. It's just that the display doesn't show s**t.

Don't rush to send it in to a "specialist". I guess it doesn't matter much in your case, since your phone runs on Android 4 and any data recovery/microelectronics "specialist" should be able to do the job. But in general, and especially in case of Android 6 and above, I suggest you try to find someone who knows how to do repairs, first and foremost. Not data recovery.
All of this is very involved, I'm aware of it. It's not for the faint of heart or for people without stamina to continue when it gets difficult. I have the curiosity, drive and energy to pursue this. Little by little, I'm improving every day.

Believe me, I'm in no rush but as blackhawk advised, it's better to be safe than screwing it up further. I will still continue to complete the testing procedure and give it to a 'specialist' only if I come across something which is beyond my current knowledge (very basic, I might add) of electronics and micro-circuitry.

There is one or two pages dedicated to listing only the components. Not sure if that's what you mean. A parts list? There is no exploded view, but there is a picture of the phone on one or two of the pages, with everything marked up for overview (anatomy). Then there is also board views, front and back, and also each side of the the sub-board (I think it's called). I don't know if I'm allowed to post it here? But you can find it online. What would you like to know from it? I can check it and get back to you.

The manual usually has two sections for parts - Electrical and Main body/Housing and I'm talking about the latter.
The anatomical view shows all the phone parts (body, housings, LCD, battery, covers, etc.) marked up with codes that correspond to the product numbers on a different list. For eg., in the pics below, you can see that the digitizer/touchscreen is marked as 'QME03' and the Parts List allows one to find out the product code for that part. In the manual I have for the G930F, it just shows the anatomy but not the actual parts list itself.

 

[Renate]

I think this component level troubleshooting may be a bit premature.
If some navigation keys are lighting up, something active is going on.
Have you definitely checked that the USB interface is totally dead?

 

[R7027]

So what you have is that any modern SoC has a "Pin Mux".

In other words "pin multiplexing" or "IOMUX"? This reminded me of "signal multiplexing". It's the same kind of idea, right? This is some old knowledge I recalled from my school days when I went to become an electrician. I don't know exactly what you call it in English, we call it "gymnasium". It's the later years of high school, it's what you might call "secondary education" I think, but instead of going for theoretical and prep school for university, I picked a practical path and started working right after that. Like I mentioned earlier in the linked forum post, we learned a lot of useful and practical things. One course we had was on how to set up everything, install cables, terminate cables, transmit and receive TV signals, do LAN installations, terminate fiber connections, etc. I was 17 at the time. Now it comes all back to me... I remember we blew up a lot of big capacitors for "fun"! Before the teacher comes, we would open the window to clear the air. But he always knew we've been up to no good. I'm in my 30s now and considering going for electronics engineering.

So what you have is that any modern SoC has a "Pin Mux".
Usually that means that every single pin can be a GPIO. Some of these pins could be UARTs. Some of them could be I²C.

As I recall it, I2C is what allows us to flash or reprogram BIOS chips in-line on Gigabyte PC motherboards without having to de-solder them, right? This is like the replacement for UART? There is one more new standard I don't remember the name of now. Can you recommend some electronics kit or something where I can toy with this type of stuff?

Another job of the Pin Mux (really the Pin Pad configuration) is to set whether a pin is an input/output/both, how hard it drives an output, whether an input has resistors to pull it up or down and for some chips whether the pin works on 1.8V or 3.3V logic levels.

This was very useful information! Thank you for sharing. I mean the whole segment on pin multiplexing. I didn't know this was possible. This is nothing short of amazing!

As far as test points go. Most circuit boards have tiny gold dots that allow for connection for testing.
For instance, you want to be able to test if the board will power on without the little button board for the power switch connected.
So they put a little dot that can be probed by a "nail" or "pogo pin", a spring-loaded contact.
You'll probably see a group of three of them around the VolUp/VolDn/Power.

I don't know about These test points look like soldering pads, right? I have not examined the board in great detail, I will have to look at it again to be sure. But now that you mention this, you remind me that I was unable to find one specific test point on this board that it's supposed to be there. Could it be that test points are these flat contact points that have been painted over or covered by the blue stuff that the top cover of a PCB is made of, and that it needs to be scraped or scratched to make contact? Like a contact point that's protected and only made to be scratched to make contact when needed, like the emergency window breaker hammer on a train or tram? I can upload a picture so you can see what it looks like. I should probably make it a new post so we don't derail this post completely. Only signal name is given in SCREAMING_SNAKE_CASING_STYLE_LIKE_THIS (is this a thing for signal names?) but I think I have located the corresponding test point TP123456 (some number, I don't have the name right now). But I can't probe it with my multimeter test leads. I will show you.

You're telling me that you're measuring 3.7V on a resistor that goes to the power button?
That seems to be the full LiPo voltage. When you press the power button you see no difference in the voltage from either end of the resistor to ground?
If you can, take a good high-res photo of the area right there.

Reading from my notes now. When I press the button, I see 3.55 V. If I let go of the button, it goes back to 0 V. This is on battery power, and battery measures 3.76 V. I'm not sure what side of the resistor I put the test lead on. I will do a new test and report back. This was done on board number 2. I have 4 of these boards, 1 of which is in a fully functional phone that will be disassembled soon (the others are all broken to some degree but they all died in the same way).

Most modern Androids do OTG just fine (with an OTG adapter).
There can be problems if the peripheral is looking to be supplied with too much current.
You can use a hub on OTG. The "input" goes to the OTG adapter, one of the "outputs" goes to the peripheral.

I found a discussion about the compatibility of Seek Thermal Compact camera on EEVblog forum. People were discussing different models, but the conversation started off with the Compact XR model and its lack of compatibility with Galaxy S9 Plus. From what I understood, the American version and Asian version of this device was somehow designed or wired differently, different from the global version and European version, which made it useless as a companion for various thermal cameras, including those from Seek Thermal.

Many found the solution in using some type of OTG dongle/adapter, and making sure to connect the adapter first, and then the thermal camera to that. The original poster reported also some funny finding, where he could sort of pre-heat or kick-start that thing in a different phone to get its juices flowing, and then moving it over to Galaxy S9 Plus and it would work just fine.

So I think you're right about current draw. Looks like they require more startup current than the phone can deliver. They used old model of camera with microUSB connector, mine is USB-C so it should work OOB but it doesn't. So I will try some kind of OTG solution before I return it.

 

[R7027]

Thanks. I wasn't aware of this fact so it's a nice way to learn on the fly.

Yup! I think it's called flying by the seat of one's pants.

I know I was a little mad when I first learned about this, because this enforced encryption significantly reduced my chances of data recovery, and nobody asked me if I want this or not. They just assume I'm a secret agent and I need double encryption on my phone. They didn't do that on Android 5 even though FDE (full disk encryption) was added already in Android 4.4 if my memory serves me right, but it was never mandatory, you had the choice to enable it if you wanted to. But not anymore, not since Android 6. It's completely done in the background and without your knowledge. Even if you don't have a PIN or password on you phone, it's still encrypted, it uses it's own internal encryption keys that are generated during production of the phone at the factory. I did a whole write-up on this over on Reddit. I think it was on Android 8 they made it even more difficult by switching from FDE to FBE (file based encryption) where every single file is individually encrypted. And there is no option to turn this off, not unless you root your device or something (and maybe not even then).

The difference in the temps of the area that gets heated versus the rest of the board is apparently enough to realise that it's not normal. I have found 2 capacitors near the processor that are not giving out any readings in either direction.

What should the reading be? Do you have a reference value? I'm not sure about capacitors, but resistors can behave differently when they are measured in the circuit vs. when measured out of circuit. So to be absolutely sure you have to remove them and measure. Maybe it's the same with capacitors. I'm not sure.

The manual mentions some kinda jig that Samsung service tech uses for diagnostics and repairs. Also to measure the frequency of the oscillator, one needs an oscilloscope which I do not have access to currently.

That "jig" might be a reference to Samsung's magical/mythical "Anyway" box. You can buy those now on Ebay, so they are no longer that secretive. There was a nice report on this on XDA actually, that's how I learned about it. Then I learned some more and learned that I can make my own UART cable without any box, and that there are other, better boxes available that can do the same thing that box does. Anyway!

I have been referencing the boardview in the manual and checking the resistors, diodes and capacitors all over the board. The caveat here is I do not know which components are to be tested in forward bias or otherwise (i.e. red probe on ground vs. black probe on ground). Moreover, I'm yet to learn how to measure/test SMD inductors so as to find out any possible shorting of those components.

Same thing here. It's like walking blind through a mine field. I put the red on ground first, in continuity/diode mode, I probe with the black, and then I switch around and put black on ground and probe with red in voltage mode once I know (or think I know) which point is ground on the component. I think this is the right idea. Flying by the seat of my pants here. I've been learning mostly from YouTube guides. There is one guy from England that I think is excellent at explaining things. His channel is called Adamant IT. Check him out.

I get what you are saying with 'invisible' capacitor. I realised about some of those being on the board only after zooming in on some macro pics I'd taken of the mobo!

Yup! I still don't have that microscope I was going to order. With holidays closing in and all that things have slowed down. I may try to hot air that capacitor back on dry, without a microscope. Before my cat sniffs it up his nose or something.

It's important to have good lighting. One thing that many overlook I think. I take help from my expensive Olight Seeker Pro 2 flash light, which is very strong. By pointing it at different angles and bouncing the light off the walls, I was able to snap some pretty impressive pictures with my new Galaxy S22. Pictures look like they were taken by a microscope. Lighting can mean the difference between being able to read the fine print on the chips and only seeing a black square. I also use a Energizer headlamp, cheap but strong and useful.

Yes it has power. I see the menu and back keys light up in addition to the service/charging led and vibration. It's just that the display doesn't show s**t.

It might be the secondary power supply for the display that's gone? There is at least two power rails and each has its own power IC, there is one for main power and one for display. This is according to my limited knowledge of mobile phone circuits.

 

[Rizzi87]

Yup! I think it's called flying by the seat of one's pants.



What should the reading be? Do you have a reference value? I'm not sure about capacitors, but resistors can behave differently when they are measured in the circuit vs. when measured out of circuit. So to be absolutely sure you have to remove them and measure. Maybe it's the same with capacitors. I'm not sure.

I'm not referencing any values to measure them yet. I'm simply testing them for continuity using the multimeter. Those 'dead caps I mentioned did not show any readings and associated continuity buzz in either direction. If I'm doing something wrong, kindly advise.

That "jig" might be a reference to Samsung's magical/mythical "Anyway" box. You can buy those now on Ebay, so they are no longer that secretive. There was a nice report on this on XDA actually, that's how I learned about it. Then I learned some more and learned that I can make my own UART cable without any box, and that there are other, better boxes available that can do the same thing that box does. Anyway!

Yeah, I got to know about the mystical jig just a few days back. I haven't bothered much about it yet since I think the probable cause is some component shorting out.

It might be the secondary power supply for the display that's gone? There is at least two power rails and each has its own power IC, there is one for main power and one for display. This is according to my limited knowledge of mobile phone circuits.

With due respect, I'll not derail your thread further with discussion of my busted Grand Neo (will continue it on my thread)
Will talk about G930F here although it will have to wait.

Btw, were you able to check out the manual for the Parts list?

 

[R7027]

I'm not referencing any values to measure them yet. I'm simply testing them for continuity using the multimeter. Those 'dead caps I mentioned did not show any readings and associated continuity buzz in either direction. If I'm doing something wrong, kindly advise.

With power on or power off? That's the catch. How to probe without knowing where ground is on the component? Continuity testing and resistance testing is done with power off. Voltage measurement (it's technically not "testing") and current measurement is done with power on. But you risk shorting the components to ground all by yourself if you put one of the test leads (usually the red or positive) on the wrong pin or pad. So to prevent this, most multimeters will have something called diode mode that can be used. In a diode, current can flow in only one direction, so in case you put the test lead on the wrong pin or pad, the current would not be able to flow back to ground through your multimeter. I believe this is what you call "forward bias", but I'm not familiar with the term.

Continuity is technically a measurement of very low resistance. I'm not sure how low it needs to be, but if we assume the limit is 100 Ohms, then the multimeter would buzz in continuity mode if it measures a resistance of less than 100 Ohms, and if it's 100 Ohms or above, it would not buzz or it might buzz intermittently and display the measured value. This will depend on your multimeter make and model. Many will have a combined continuity and diode mode, all in one setting. I have one of those. It's an old digital multimeter from Velleman. It's not very expensive or accurate, it doesn't even have auto-ranging, but it does the job.

So this is the general idea I believe. As an electrician I would normally only measure voltage and current in electrical installations of a building. I have a Fluke instrument for this where one of the test leads is built into the instrument so you can easily get the reading while holding it, and then the other test lead hangs loose by a wire. So I normally know where ground is, I don't have to stand there and guess. It's easier working on a big scale electrical circuit like in a building and you can see clearly where everything goes, or it's labeled appropriately. I only learned about diode mode when I started working on this phone.

Btw, were you able to check out the manual for the Parts list?

I was going to get back to you as I didn't have access to my other computer. I have checked it now. You're asking for Galaxy S7, right? I don't have the complete manual. I only have some chapters from it.

This is table of contents for the manual:

1. Safety Precautions
2. Specification
3. Product Function
4. Exploded View and Parts list
5. MAIN Electrical Parts List
6. Level 1 Repair
7. Level 2 Repair
8. Level 3 Repair
9. Reference data

I have chapter 2, 5, 7 and 8. You want chapter 4, right? I don't have it. I have looked for it but could not find a complete manual anywhere. Chapter 7 contains the overview picture I mentioned with the different components marked up, like "SIM Socket", "Motor", "Volume Key", etc. I understand now what you want and this is not it. But I have come across the exploded view chapter for the Galaxy S7 Edge phone, which is very similar. That might be helpful?

 

[R7027]

This is the overview picture from chapter 7 of Galaxy S7 (SM-G930F) manual.

 

[R7027]

I have attached a PDF containing exploded view of parts and parts list for Galaxy S7 Edge (SM-G935F). It should be almost identical to Galaxy S7 (SM-G930F).

Here is the layout of top side:

And here is the layout of bottom side:

 

[R7027]

To answer my own question now and to clear up anyone confusion anyone else might have, this is how you measure voltage at a resistor with a multimeter.




Black (negative/ground) test lead on a grounded contact point, like the metal shields in this example, or the metal surface of screw holes. Red (positive) test lead on the positive pin or contact point of the resistor. If you don't know which is which, you need to either check a circuit diagram if you have one or use diode mode and continuity test on your multimeter to figure it out.

In this situation, voltage was about 3.7 V when the power button is pressed, which is full power of the battery. It goes back to 0 V when the power button is released. You do need a power source too, like a battery or a DC power supply. This should be obvious. I don't have a battery connected in these pictures as I only took these pictures for demonstration purpose.

@Renate I didn't check both sides of the resistor as I currently can't take a good reading on this board, because I knocked off a tiny capacitor from the other side of the board as I was taking off the shields, and I'm getting bad readings all over the place. So I need to put that thing back on before I can toy any further with this, and for that I need a microscope. But I have a fresh and fully working board of the same type, in a brand new phone of the same model that I will cannibalize.

 

[Renate]

Samsung was famous for using the USB 2.0 ID pin to switch into different modes.
This was the point of the AnyWay jig.
If this is an older micro USB connector (and not USB Type C) there might be something to do in this direction.

Another useful technique is to monitor battery current.
You need to remove the battery and replace it with a current monitoring power supply.
Then you can see if your device is even trying to power on and boot.
Here's a plot of around 2 minutes of a device (which, I forget) booting up.

99.9% of all capacitors are directly across power rails.
In regular ohm setting on a DVM they should probably measure open.

We can see that the power switch is working.
You have to see if the USB is doing anything.

 

[R7027]

Samsung was famous for using the USB 2.0 ID pin to switch into different modes.
This was the point of the AnyWay jig.
If this is an older micro USB connector (and not USB Type C) there might be something to do in this direction.

Yes, Galaxy S7 uses micro-USB-B connector. It looks like pin number 4 is the ID pin, it sits between GND and DATA+ pin. How was this related to AnyWay jig?

Another useful technique is to monitor battery current.
You need to remove the battery and replace it with a current monitoring power supply.
Then you can see if your device is even trying to power on and boot.
Here's a plot of around 2 minutes of a device (which, I forget) booting up.

Thanks for the tip! And thanks for sharing that picture, it's really cool to see how the graph goes up and down like a beating heart.

I did actually buy a DC power supply that came with a Modbus to USB interface and a software, but I never got to use it. I don't have the special cable needed to attach to the battery connector on the board. Is this how you do it also? What cable do you use? What do you call this type of cable? So I know what to search for. I'm a bit at lost as to what to buy. There is one called "Mechanic iBoot Box" that seems to be very popular. Is this the right thing? Can you advise me on what to consider when buying one of these? Does it need to have a current limiter for example? My DC power supply already has current limiter (and voltage limiter I think), over current protection (OCP) and over voltage protection (OVP).

We can see that the power switch is working.
You have to see if the USB is doing anything.

This is something I need to explore in more detail. Again, thanks for the tip!

I will make a separate post on "AP_PS_HOLD". But this is supposed to be 1.8 V and as I understand it this is something that goes into the CPU/SOC. So maybe this is the voltage you have been asking about. I'm not sure how this works, or what this cryptic signal name means. But I suspect, that this is what sustains power to the CPU, once the power button is pressed.

 

[Renate]

Yes, Galaxy S7 uses micro-USB-B connector. It looks like pin number 4 is the ID pin, it sits between GND and DATA+ pin. How was this related to AnyWay jig?

Some(?) models of Samsung used a 5 bit ADC that measured the log of resistance to ground of the ID pin.
The range was from direct short (0 ohm, for OTG) to 980 kohm. There were different modes assigned to each ADC reading.
Lol, I just googled it and I came up with myself. https://forum.xda-developers.com/t/samsung-resistors-on-usb-id-pin.3316735/

I don't have the special cable needed to attach to the battery connector on the board.

As far as physically connecting, I've sometimes used a battery-shaped scrap of plastic and some pins.
For junk/permanent battery-ectomy I just solder.
If you are removing the battery, your solution has to support all the functions provided by the battery.
That is quite often a 10 kohm NTC thermistor to ground (just replace with a 10k resistor) and often some ID resistor that identifies the battery pack.
You can carefully measure your battery pack for resistances from any pin that is not + to the ground pin.

I will make a separate post on "AP_PS_HOLD".

I presume that is the "Application Processor power supply hold".
That is not so much an SoC signal as a usage for an SoC GPIO.

In any case, I think that you're diving in too deeply into the grass before you have an idea if this thing is even trying to boot.

 

[Rizzi87]

I think this component level troubleshooting may be a bit premature.
If some navigation keys are lighting up, something active is going on.
Have you definitely checked that the USB interface is totally dead?

Kindly excuse me if your message was directed toward me and I didn't reply earlier. I haven't delved into component troubleshooting for the S7 yet since the display problem with it is most probably due to physical damage and I will confirm it at a later stage. I was referring to testing on my GT-i9060

What should the reading be? Do you have a reference value? I'm not sure about capacitors, but resistors can behave differently when they are measured in the circuit vs. when measured out of circuit. So to be absolutely sure you have to remove them and measure. Maybe it's the same with capacitors. I'm not sure.

As I mentioned, I am just testing them for continuity with the phone switched off as this was the method shown on a couple YT videos to trace out a 'bad' capacitor.

It might be the secondary power supply for the display that's gone? There is at least two power rails and each has its own power IC, there is one for main power and one for display. This is according to my limited knowledge of mobile phone circuits.

Sorry for not mentioning the physical damage on my S7 screen earlier, which I believe, is the cause for the screen not powering on.

To answer my own question now and to clear up anyone confusion anyone else might have, this is how you measure voltage at a resistor with a multimeter.

View attachment 5777521
View attachment 5777523

Black (negative/ground) test lead on a grounded contact point, like the metal shields in this example, or the metal surface of screw holes. Red (positive) test lead on the positive pin or contact point of the resistor. If you don't know which is which, you need to either check a circuit diagram if you have one or use diode mode and continuity test on your multimeter to figure it out.

I am currently perusing a couple of boardview/schematic softwares and while I haven't been able to utilize even a fraction of its potential, I have been able to determine ground contact points for components on the mobo and the associated 'net' for each component. From there, I have been able to partially understand schematic diagrams.

Which brings me to my next project-in-queue. Well, it was sort of dumped onto me!

I've got a Samsung Galaxy A10 which shows signs of boot-up (vibration and battery charging sound notification) but the display doesn't turn on. The phone has no apparent physical damage although the LDI has turned pink hinting at water ingress. Today, it even sounded the alarm (f***ing 5 in the morning!) which may have been set before the display went blank proving that the phone is in working condition except the display.

**NOOB ALERT**

I pulled up the service manual/schematic for the A10 and with my limited knowledge, started off with troubleshooting the LCD display connector as per the manual:

Now, I've identified the pin for VDD_LCD_1P8 on HDC7003 and the capacitor connected to it but I have no clue how to measure 1.8v on that line. Do I measure it from the pin to the capacitor or from the pin to ground? OR is it supposed to be measured elsewhere?

Like always, any help is greatly appreciated

 

[blackhawk]

Meh, unless you're doing it for education or amusement it's more productive to treat it from a block rather than component level prospective. Replace the defective switch assembly, etc or pcb.
A parts queen is nice to have...

Mind your ESD protocols as individual out of circuit pcbs can be very suspectable to ESD damage. The less invasive and prolonged the repair effort is, the less the possibility of you causing unintentional collateral damage...

 

[Rizzi87]

Meh, unless you're doing it for education or amusement it's more productive to treat it from a block rather than component level prospective. Replace the defective switch assembly, etc or pcb.
A parts queen is nice to have...

Mind your ESD protocols as individual out of circuit pcbs can be very suspectable to ESD damage. The less invasive and prolonged the repair effort is, the less the possibility of you causing unintentional collateral damage...

Yes. Apart from the satiating feeling of understanding how these things work, the educative aspect entices me just as much. This phone, the S7 or the GT-i6090, though not being primary, serve as temporary replacements so I intend to try to fix them.

Owing to the above reason, I'm trying to figure out why the lcd isn't working rather than replacing it outright unless I'm sure that it's beyond repair. Hence the component level approach.

ESD damage was among the first things that I discovered when trying to dig out information on repairing mobile phones. An anti-static ESD mat is my next purchase; I already have the wrist strap.

 

[blackhawk]

Yes. Apart from the satiating feeling of understanding how these things work, the educative aspect entices me just as much. This phone, the S7 or the GT-i6090, though not being primary, serve as temporary replacements so I intend to try to fix them.

Owing to the above reason, I'm trying to figure out why the lcd isn't working rather than replacing it outright unless I'm sure that it's beyond repair. Hence the component level approach.

ESD damage was among the first things that I discovered when trying to dig out information on repairing mobile phones. An anti-static ESD mat is my next purchase; I already have the wrist strap.

In that case carry on...

Using an earth grounded mat and strap help reduce the voltage potential but not eliminate it.
The idea is to quickly bled off charges but with some resistance to avoid causing excessive current through what you're trying to protect as a direct path to earth ground would do.

Raising the RH to beyond 40% will help dissipate charges faster. So a boiling kettle of water in the room... In a dry room the static potential builds quickly and lingers, even crunching a sheet of paper can generate a couple hundred volts. Anti static plastics also build a charge. With a static meter it's rather surprising to see how prevalent static electricity is. It's all around us. Any motion can potentially produce it. Human threshold of perception of it is about 400 volts, already more than enough to cause damage.