Thinkpad a21 works only with externally charged battery

Hi @dvdmcwilliams ,

Just verifying that the laptop doesn't start with the charger connected only. Is this correct?

It may be that the DC-In jack is either faulty or has become disconnected from the systemboard.

Here is a link to the service manual for your laptop.

Scroll to p.91 to view the necessary pre-requisite steps and then the procedure to remove the systemboard. I think that this is where the DC-In jack is connected.

Once you have gained access to the systemboard you can test the jack using an Ohmmeter to prove whether it is the problem or not. You will need soldering expertise and tools to effect the test and repair.

Here is a link to just one supplier of the replacement part. it is not a recommendation to use them. it is shown to give an idea of what the part looks like and how much it costs. There are other suppliers online that may suit you better. Just search for IBM Thinkpad A21M DC-In jack part to get results

Hi @dvdmcwilliams ,

From your description it appears as though the power supply circuit from the battery to the laptop is OK but the supply from the charger to both the laptop and the battery is not. According to the service manual the laptop should start with just the charger connected (no battery inserted).

Can you see if there is anything obviously amiss on the motherboard between the fuses and the battery connector? (Assuming that this is where the power regulators would be situated - apologies if you've already been there, done that).

Also check if there is any voltage present at all when measuring between terminals 1 (+ve) & 5 (-ve) of the motherboard's battery connector (with the battery removed). Looking at the manual there should be 12.6 VDC present when testing between these battery terminals on a fully charged battery, with the battery out of circuit, so there must be a similar if not slightly higher voltage there to charge the battery.

(Proviso - it may be that there is no power to the battery connector terminals with the battery removed as the charge circuit may rely on "knowing" that the battery is inserted to start charging due to a 4K Ohm - 30K Ohm circuit requirement between terminals 4 & 5 in the battery, see p.37 in the manual. I don't know whether it will or won't)

Unfortunately IBM/Lenovo have not released any schematics for their products (or none that I can find relating to yours).

You could try searching online using the motherboard's 'board' number + schematic in the search term and see if there are any results.