sub board when charged shows that voltage gets in, but none out (A70)

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Samsung Galaxy A70

Commercialisé en avril 2019. Numéro de modèle : A705FN/DS.

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Elijus Skersys @elijusskersys

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Publié: 28 mars 2025

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sub board when charged shows that voltage gets in, but none out (A70)

So I'm Having problems with charging my A70. I am checking voltage everywhere, I know it's not the flex cable because power goes through it, and the next thing I'm trying to understand, when I'm checking whether the power from the charger reaches further than the inlet. I get 5.23V when I test the positive side, but when I try the negative side, it doesn't even show -0.001, only 0.000.

Is the problem me or something on the sub board? (I took out the sub board from the frame, put the charger in while all the connectors were taken off and then measured

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jayeff @jayeff

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Publié: 28 mars 2025

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Hi @elijusskersys

Here's the troubleshooting section from the service manual for the phone.

Go to Sect. 8-4-6. Cable Charging Part on p.12 (of 40) and follow the flowchart to see how far you get.

Use the search function in your pdf browser (Ctrl + f?) to search for the component's designation to find their location on the board layout diagrams in the guide. You will have to zoom in a lot to see them.

Unfortunately there's no parts list in the manual so if a component is faulty e.g. capacitor or IC then it will be very difficult to find a replacement as their specifications most probably aren't shown on them

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Hello, but isn;t this too far for a beginner? My father is saying that this is too complicated and I should check the sub board's voltages, which I have, multiple times.

30 mars 2025 par Elijus Skersys

@elijusskersys

Check the voltages is precisely what the flowchart is telling you to do. They may not all be on the sub board though. It is telling you where and what value voltage to check, it saves guessing where and making assumptions what is should be.

It is hard for a novice, but you're trying to find a problem at component level on a board. Why would you think that it would be easy?

At least you have the flowchart telling you the checkpoints to test and the board layout diagrams telling you where they are.

Using the search function will show you the location of the components mentioned in the flowchart, in the board layout diagrams in the manual.

Unfortunately if it is a faulty component and it is not on the sub board but on the mainboard then there's no parts list which you help you to just change the component and not the whole board. Then you would need to have smd (surface mount device) soldering skills and tools as well

It would be a lot more complicated if you didn't have this information.

30 mars 2025 par jayeff

@jayeff so I still need to take off the shield that guards all of the components, am I correct?

31 mars 2025 par Elijus Skersys

@elijusskersys

If that's where the components mentioned by the charge problem flowchart are located then yes.

There may come a time during the repair that you may have to decide whether or not to continue with the repair.

For example:

If you find that the problem is a faulty component then as most have no identification on them and there's no parts list (or schematic) to identify them it will be difficult to find a replacement part.

If the problem is due to an open circuit between two of the components mentioned i.e. voltage is correct at one test point but not at the following test point in the flowchart then as the board is a multi layer board you may not be able to find where the problem exactly is unless it is an obvious break in the board (has the phone been dropped or gotten wet, shortly before the charging problem started?), so you may not be able to fix it either.

Not trying to deter you, just pointing out the realities of home electronics repair.

1 avr. 2025 par jayeff

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Hello, but isn;t this too far for a beginner? My father is saying that this is too complicated and I should check the sub board's voltages, which I have, multiple times. — Elijus Skersys
@elijusskersys

Check the voltages is precisely what the flowchart is telling you to do. They may not all be on the sub board though. It is telling you where and what value voltage to check, it saves guessing where and making assumptions what is should be.

It is hard for a novice, but you're trying to find a problem at component level on a board. Why would you think that it would be easy?

At least you have the flowchart telling you the checkpoints to test and the board layout diagrams telling you where they are.

Using the search function will show you the location of the components mentioned in the flowchart, in the board layout diagrams in the manual.

Unfortunately if it is a faulty component and it is not on the sub board but on the mainboard then there's no parts list which you help you to just change the component and not the whole board. Then you would need to have smd (surface mount device) soldering skills and tools as well

It would be a lot more complicated if you didn't have this information. — jayeff
@jayeff so I still need to take off the shield that guards all of the components, am I correct? — Elijus Skersys
@elijusskersys

If that's where the components mentioned by the charge problem flowchart are located then yes.

There may come a time during the repair that you may have to decide whether or not to continue with the repair.

For example:

If you find that the problem is a faulty component then as most have no identification on them and there's no parts list (or schematic) to identify them it will be difficult to find a replacement part.

If the problem is due to an open circuit between two of the components mentioned i.e. voltage is correct at one test point but not at the following test point in the flowchart then as the board is a multi layer board you may not be able to find where the problem exactly is unless it is an obvious break in the board (has the phone been dropped or gotten wet, shortly before the charging problem started?), so you may not be able to fix it either.

Not trying to deter you, just pointing out the realities of home electronics repair. — jayeff

Samsung Galaxy A70

sub board when charged shows that voltage gets in, but none out (A70)

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