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Android tablet pcb

looxuser

Dec 28, 2015
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Evening all, so i'm in the process of attempting a reapir of my android tablet that fails to startup after charging via the usb port. Before i get into that in a separate post I wanted to discuss different types of pcb used in electronics; So i've attached some images of both sides of the pcb. The components are tiny so its difficult enough to determine what components they are but establishing the connection between them becuase there are very few tracks on the board. So in relation to the images can somebody help answer these questions please:-
1. The components seem to be grounded on once side to this huge ground plane and I assumed the other end went through the board to the other side but in the position they would be only seems to be another huge area of copper. take the images below, in the first one you can see the dc supply the two wires upper left, yet on the other side of the pcb image 2 theres nothing seemingly there, no solder pads, tracks. I wondered if these are over painted but it doesn't seem so.
2. The 5 pin connector is where the lion battery connects, the centre pin being the thermal sensor for control of the battery temp, either side is two positive or negative feeds. I assumed the large resistors R020 would be involved in the power circuit given their size but these are nowhere near when those +ve & -ve would emerge from the other side of the board?
3. That chip bq7510 (and i cannot determine what its is for sure) seems to be a DC to DC regulator of some kind or a lion battery fuel gauge now that has tracks going off to the small resistors and diodes either side but then the other side of these components disappears, must be through the board but to what?
4. you can probably just make out those black components labelled f1 with two bars one end. Any idea what they are?
5. You can also see tiny dots all over the green areas which i assumed were through hole but they don't necessarily correlate to solder pads on the other side of the board. On those copper circles there are punch marks which i assume are automated test points. You've got to appreciate the technology in use here, these are tiny and it beggars belief how they make probes that small in the first place, amazing.
6 Any idea how to lookup the CHT component with such little markings?
7 just for general insight, i see these smd components can be grey, brown or black. what do the body colors mean. I assume brown is a cap, grey a resistor and black a diode but could be completely wrong.

Any insights appreciated. The slight serrated edge of the board btw is a good reference point it aligns to the +ve pad (red wire) and the multi connector.

On the repair front my first port of call was to probe around the board and see where the battery supplies were going but reluctant to do this until is established what went where through fear of damaging something. I suspect the USB charging port has overloaded something so its just determining what. I'll post the circuit diagram which is hard to follow for me in a separate post but it may instant mean something to you guys.Img_3976.jpg Img_3972.jpg
 

davenn

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Sep 5, 2009
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hi there

1. The components seem to be grounded on once side to this huge ground plane and I assumed the other end went through the board to the other side but in the position they would be only seems to be another huge area of copper. take the images below, in the first one you can see the dc supply the two wires upper left, yet on the other side of the pcb image 2 theres nothing seemingly there, no solder pads, tracks. I wondered if these are over painted but it doesn't seem so.


the first image is really dark and blurry, cant really make anything of it

only a few of the components might have one side connected to the ground plane



2. The 5 pin connector is where the lion battery connects, the centre pin being the thermal sensor for control of the battery temp, either side is two positive or negative feeds. I assumed the large resistors R020 would be involved in the power circuit given their size but these are nowhere near when those +ve & -ve would emerge from the other side of the board?

cant tell because of the bad pic

3. That chip bq7510 (and i cannot determine what its is for sure) seems to be a DC to DC regulator of some kind or a lion battery fuel gauge now that has tracks going off to the small resistors and diodes either side but then the other side of these components disappears, must be through the board but to what?

BQ7510 from what I can discover, is a charge controller IC

other components ...... this will guaranteed be a multi layer board, could easily be 3 - 4 layers and impossible to trace

4. you can probably just make out those black components labelled f1 with two bars one end. Any idea what they are?

probably tantalum capacitors .... also possibly a diode


5. You can also see tiny dots all over the green areas which i assumed were through hole but they don't necessarily correlate to solder pads on the other side of the board. On those copper circles there are punch marks which i assume are automated test points. You've got to appreciate the technology in use here, these are tiny and it beggars belief how they make probes that small in the first place, amazing.

they are plated through holes called vias, in this case they connect one ground plane with another one


6 Any idea how to lookup the CHT component with such little markings?

try googling SMD marking CHT


7 just for general insight, i see these smd components can be grey, brown or black. what do the body colors mean. I assume brown is a cap, grey a resistor and black a diode but could be completely wrong.

doesn't mean anything in particular


Dave
 

kellys_eye

Jun 25, 2010
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What make/model Android tablet? Have you Googled for common startup faults associated with your particular device?
 

kellys_eye

Jun 25, 2010
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I've come across similar problems at startup on low-end models that relate to the USB charger socket and daughter board it's all constructed on. Faults like this are quite common - enough so that after-market suppliers offer replacement boards (modules) for a straight swap-out repair.
 

looxuser

Dec 28, 2015
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Dec 28, 2015
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thanks davenn for the point for point responses, re "BQ7510 from what I can discover, is a charge controller IC" depending on cost of that IC might be worth a swap out . Heres a part of the schematics from Huawei, think middle diagramn relates upload_2017-7-14_14-19-48.png Without tracks and reference color of those SMD components its hard to know which are which and be able to test inputs to charge IC. Any ideas or indeed by-pass to force a start up of the tablet please?
 

kellys_eye

Jun 25, 2010
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Does any of the technical information you have show the parts placement?

In its simplified form, the circuitry takes the battery volts and applies it via various SMPS devices to obtain all the required voltage rails used in the device - anywhere from 1.8V to 5V or 12V - a separate SMPS device for each voltage.

Additionally to that you have the charge controller that ensures the relevant voltages are 'switched on (or off)' in the appropriate order OR 'off' if there is a short/fault somewhere.

If you identify the individual circuits you can check for the voltages that SHOULD be there and the control signals that make them turn on.

The diagram you show reveals THREE such SMPS circuits (not very clearly) and what appears to be the controller. But that doesn't necessarily mean this is where the fault is. A short-circuit (or overload) somewhere else may be shutting the thing down.

What we would need to know are the measurements you've made, where you made them and indicated on the WHOLE schematic.

That said, if a device like the charge controller needs replacing, do you have to tools/skills necessary to do that?
 
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