My S7 is dead... Can anyone help?

[automobilklub]

Hello again. I know it's been a while since my last post. I managed to replace the power management ic (PM7540) but that did not change anything. Still no power or charging indication. I have checked the power on status and cpu voltages and all seem to be fine. So power manager is ok I presume.
Is it possible to brick the Huawei S7 by improper software upgrade attempt? I mean, to overwrite the NAND memory so it has wiped the bootloader and power table? That's the only thing I can think about at the moment. Every single component seem to be ok. If you have any suggestions, please do not hestitate to write it down here. Thank you!

 

[automobilklub]

Ok. Finally, after few months of the battle with physics/electronics and bad luck, I decided to take apart my S7-103 and sell it for spares. I think, someone with manual/troubleshooting could repair it (I have not messed it up inside-no damage or missing components). But as I fed up-it goes as it is. Tried to find appropriate category here, but I couldn't. Can someone guide me to buy/sell thread, if it exists?
If not, I will sell the complete lcd/touch module in very good condition, no scratches etc, new battery and faulty mb. Psu also ok, but I have cut the cable to measure consumption-works well though. Or maybe all together, if someone wish to try to fix it. I'm in UK by the way.
Sorry mods if this is wrong place for this-please move it to correct topic if you don't mind.
Thanks

 

[cadiman]

One thing I have learned on these is the battery should be fully charged. Most will power up with the charger plugged in but sometimes the charger sends junk in along with the charge voltage (poor filtering on a switching power supply messes with the processor).

I check battery voltage with the power pack plugged in and make sure it is getting voltage above what the battery was reading before plugging in the charger.

Like on sylvania 7" tablet there is a 3.3volt regulator that runs the main board. These will fail and go low (2.7v) The device needs 3.3v and will not run on 2.7volts.

These look like a miniture transister and are surface mounted. (found all over flat panel tv boards)

Also check the surface mount fuse (follow power adapter input and use your meter set to ohms) and should not be open.

The fuses are hard to spot if you are not used to looking for them. Follow the positive lead in (from power adapter) and look for white rectangle surface mounted object on the board.

Next to it the board will be marked "F101" or something like that.

The batteries on these are single 3.7 volt (5volt charger) or two 3.7 volt batteries in series (9 volt charger).

If that doesn`t help I start looking at diodes. These short out and bring the whole system down.

The larger tablets may have capaciter issues (found in everything else. Why not tablets?)

I am still learning these but I get a little better each day.

I am more familiar with coby 7015s for now.

Again, I am new here and still finding my way around. If this is the wrong place for this topic, Sorry.

 

[automobilklub]

Hi there. Thanks for your answer. I can tell you that I have tried literally everything. Checked smallest components on mb (I repair mobile phones at work), have access to every equipment I need. There are some voltages on mb so I have eliminated fuses and diodes failure. Battery voltage does not go higher when plugged in, in fact it slowly discharges over the time. I have charged it externally to 3,9V and left it in tablet over night. In the morning was only 3,5V. So short circuit I would presume. But when measured the current taken from battery in tablet, it was like 0.03A, so nothing basically. Battery is new btw. The only thing i'm not sure about is testing capacitors while they still soldered to the mobo. Even if those are not shorting, there is no certainty they ok, right?
Thanks again and will see if I can do anything else with it.