What is laptop battery charging section repair issues
In laptop chip level repair there is the main problem that comes in preparing is the laptop battery charging repair-related issues. It is one of the most reported issues by customers and enthusiasts.
The reasons can be anything but the main cause is that the laptop adapter is not able to provide 19v current to your laptop. More issues can be there like like motherboard issues. We will cover them separately in another blog.
How laptop handle laptop battery charging repair
There are two types of mechanisms used in the laptop battery charging repair section.
Let’s see them one by one.
1. Buck Converter :
Single-phase synchronous converter and has the same working. This consists of a mechanism in which one high side MOSFET and one low side MOSFET turns on-off alternatively to turn down the voltage from 19v to 12.6v which is necessary for a laptop battery.
2. Buck-Boost Converter :
There is a use of the first set of high-side and low-side MOSFETs which comes before the inductor. They can also work as a regular buck converter.
After it, there is a second set of MOSFETs which is used to boost the voltage coming from the AC adapter.
The main disadvantage is that it takes 5v to 20v to charge the battery. Which makes it very slow to charge the laptop.
Battery voltages in the cell of the laptop
Lilium cells make laptop batteries. These can be made up of either Li-ion cells which are like cylindrical shapes or LiPo cells which are flat rectangular.
The voltages of these change according to the brand of laptops. Typically Li-ion has a voltage of 3.6 to 3.7v. LiPo cells typically have voltage around 3.7v to 3.85v.
Troubleshooting charging circuit
1. No Power :
The first thing you will check is whether the main power rail in a laptop is present or not. If it’s present that means the problem is not present in the charging circuit. You can still check any short MOSFET for DC supply or changing ic having missing voltages. Because in some cases they can be root or trouble too.
Before it, you have to check you have HPB or an NVDC configuration. With HPB configuration you have to check the voltage after the second DC-in MOSFET. You have to find AC adapter voltage.
In the NVDC connection, you have to check voltages after the buck convertor coil and also after the fuse if it exists in that laptop model for location.
If the found fuse is burnt via checking before its voltage and after its voltage. Replace it and go to the next section for ‘short gound on the main rail’. resolve it before applying power.
2. Shorted DC-in MOSFET
There is also one issue that is very common. The issue is mostly faced by newbies in this field. There is a difference between MOSFET blocking the current and *failed*.
In the HPB technology method there can be the case that the main power rail will be present as the current will pass from within shorted MOSFET but there can be a possibility that some signals from charger IC may be missing which makes our platform unable to run.
Whereas in NVDC the main power rail may be missing. Check the resistance between the Drain/Source/Gate of both DC in the section for whether they are shorted or not. The resistance should be at least a few kilo-ohms.
3. There are burn-in current sensing lines in the laptop battery charging repair section
The overcurrent from battery adapter to battery gets monitored by charging IC. There can be burned in the current sensing circuit either in current sensing sensors or resisters that connect them to current sensing amplifiers. The easy way is to measure the resistance at the current sensing amplifier pin of the charger IC. The measured resister should be a summation of the current sensing resistor and resisters which connect them to IC.
This also takes care of any possible break of line that was happened due to any liquid damage.
4. Missing voltages on charging IC in laptop battery charging repair section
There are some voltages that are required to run the charging IC. The names can be vary depending upon the charger IC brand. But majorly,
- DCIN/VCC – Mostly it is close to the AC adapter. These are voltages coming from the AC adapter.
- ACIN/ACDET – Mostly it is required a voltage of more than 2.4v or 2.6v. It is dependent on charger IC and it uses the voltage divider to get the current-voltage range.
- REGN/VDD – It has internal LDO output mostly between 5v to 6v. The input for this output is taken from DCIN/VCC.
The following signals should come after coming previous signals.
- ACOK – It denotes the input voltage is good. In the case of P-type MOSFETS, it drives MOSFET gates directly.
- ACDRV – Only present in the n-channel type of MOSFETs. Mostly cases it is around 25v voltage which should minimum of more than 6v.
5. Damaged Passive Component in laptop battery charging repair section
By doing a visual inspection we can spot any damaged capacitor or missing/damaged resister in the circuit. This comes mostly in cases of liquid damage but rarely in other cases. You can follow visual hints if you know or found that there is liquid damage.
One of the issues can be gate resisters for DC-in MOSFET, which could be near it. You can always them for precaution.
6. Dead charger IC in laptop battery charging repair section
If you go by all previous issues then the issue might be that the IC itself is dead. Check for its behavior change by replacing it.
7. Battery not charging in laptop battery charging repair section
Try multiple batteries. The problems can be the battery itself for the battery not charging. Change the battery until you found the right one. because the market is filled with garbage quality batteries. 99% of problems can be due to batteries. While some new batteries are required to ‘kick-start’ via plug-in the adapter, some come filled in with 50%, 80%, or in some cases 20% too. It is important for you to know whether you have HPB or NVDC in your circuit. Your battery should start charging 100%.
8. Battery not detected
There can be an issue with the charging circuit SM-Bus. Check all voltage modes and SM bus to the ground on SMBus SDA and SCL lines.
9. Low voltage on battery charging rails
In the case of NVDC technology if on battery charging rail there is too low voltage present the battery will not start to charge. Thye gate resister of MOSFET or MOSFET itself which is situated between buck convertor output and better power rail can be problematic. Inspect it and change it if it’s found faulty.
In HSB topology battery is most connected to the buck convertor directly. The bad battery or deeply discharged battery will pull down output. One way is to let the battery charge overnight, if this does not solve the problem then replace the battery. Without the battery, the output within the output rail will be low. DC-in MOSFET or Current sensing can be a problem in this situation.
In some chargers, ic’s the ic have a ‘CELL’ pin to control the voltages applied to batteries relative to the number of cells in series in the battery. The wrong setting in ic can cause wrong output.
10. High voltage on battery charging rail in laptop battery charging repair
Shorted high side MOSFET with buck convertor on charging rail can be also caused for it. Shorted battery to system MOSFET can be problematic in HPB technology.
You can also check our other laptop preparing help guides.
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