The battery charge circuit of the GBA SP is controlled by the dedicated battery charger IC on the earlier boards, and integrated into a smaller package (not yet reverse engineered) on later versions.

TODO: Image of both here

We will focus on the earlier 16 pin charger IC circuit for now.

TODO: Image of charger on PCB with pin names.

To diagnose the charger circuit we want to make sure mainly two things are present and valid, which are also the two things that mostly fail.

The first test is insert the charger cable into the EXT2 port of the console, and measure with your multimeter on a main PCB ground to the 5V test pad by the charger IC and measure for 5V being present.

TODO: Image showing measuring 5V.

If 5V is present you can move on to Battery Voltage To Charger checks further down. If not, continue with the diagnostics below.

Firstly, we should receive the EXT_VIN signal from the charger port (or USB-C modified port). This comes in from the port itself, through the EM8 filter (both ground and 5V), through F1, and to EXT_VIN.

Most commonly the EM8 filter blows, and disconnects the ground side (pin 4 and 3 of EM8) which disconnects pin 6 of the EXT2 port from ground. The 5V side can also fail but its usually the ground.

To test EM8, Simply get your multimeter and probe over the top and bottom pins both sides of EM8 to make sure you have continuity.

TODO: Image

If you do not have continuity from the top to bottom, both sides (so pins 1 to 2, and pins 3 to 4) then you can just remove the EM8 filter and bridge them with wires for now. You might get a little audio noise when charging doing this and you can replace EM8 at a later date with a new filter.

TODO: Image of bridged EM8

Next check the fuse F1 has continuity (0R resistance), and if it does not, again you can temporarily bridge it or replace it with a resettable fuse.

TODO: Image of fuse

Once you know you have a good EM8 filter and good fuse, insert the charger cable to provide 5V into the port, and measure from a ground point on the main PCB (after EM8) and to the 5V input pad of the charger IC.

TODO: Image of probe points.

You should receive 5V down to that point. If you do not, put your black probe on pin 6 of the EXT2 port, and the red probe on pin 2. This is the first place 5V enters the system. If you have no voltage here, your cable or port is bad (or you have a short on your board pulling it low, so measure resistance between pins 2 and pin 6, if it is low (less than 200k resistance is not normal, and less than 500R is likely a short somewhere on the console).

Once you get it there, move your black probe to the main PCB ground and if you lose 5V, your EM8 filter is bad.

After that, move the red probe to F1 and check both sides. If you lose 5V on one side, your fuse is bad. If you lose 5V both sides the trace from pin 2 of EXT2 to the F1 fuse is broken so repair that.

Finally, move the red probe to the rectangle test pad by the charger IC and you should see 5V. If so your IC is getting 5V, but to be absolutely sure you could probe directly on the IC pin 5 which that pad connects to.

TODO: Image of test pad and 5V in pin.

If we know the charger IC is receiving 5V when the charger cable is inserted, we should next check when the battery is inserted does that battery connect to the charger IC.

The first test is you should be able to insert your battery into the console, and measure between ground and pin 13 of the charger IC to see the battery voltage appear. If you do not, follow the steps below.

With a battery inserted (I usually tape it tight to the spring connector to keep it in place while I work), first measure that the battery is entering the PCB. Measure in Voltage DC mode with your multimeter over the test points on the front of the PCB labelled BT+ and BT-.

TODO: Image

You should see your battery voltage (whatever the battery measures if you measure it directly with a multimeter while not connected to the console) over the BT+/- pins.

If you do not, check it is making good contact, and that there is no short on the GBA SP board by measuring resistance between the battery springs on the PCB and it should be in the million ohms or OL reading).

TODO: Image measuring springs

If you measure a voltage on your battery when not connected, and there is no short, and when you connect the battery it doesn't get to BT+/- then check your battery spring connector looks ok and is not faulty, and there are no torn traces/vias from the connector to BT+/-.

After the battery springs, the battery ground is directly connected to the PCB ground, and the input of the BT+ passes through the fuse F2,then into pin 13 of the charger IC.

Check your F2 fuse has continuity and if not replace it with a new fuse or bridge temporarily.

With your black probe on any ground, place your red probe on both sides of the F2 fuse and check the battery voltage is present.

If voltage isn't present on F2, then check your trace from the BT+ test pad to the fuse pads in continuity mode. If the BT+ pad is not making contunity to the the F2 fuse run a new wire to repair the trace.

TODO: Image testing from BT+ to F2

The final path is from the F2 fuse to pin 13 of the charger IC.

Keep your black probe on a ground, and the red probe on pin 13 of the charger IC while a battery is connected. You should measure your battery voltage at this pin.

If you do not, then move your red probe back to the F2 fuse, if voltage is present at F2 but not at the charger IC then run a new wire to repair the trace.

If the above is all good and you are getting 5V into pin 5, and a battery voltage into pin 13, the next step is checking we are actually getting a charge going into the battery.

There are several ways to check this.

If all is well, the charge LED should come on orange and stay on. If it goes off after a second its usually because the charger IC has not detected a battery voltage so check the steps above again.

The charge LED is also just an indication and might be blown, or even work but not to be trusted (it can come on but not actually be charging the battery) so you should still perform one of the other checks below.

If you have an upgraded USB-C charging port, you can connect a USB current meter inline with the charging lead and monitor the current being drawn when you plug it in.

The battery should charge at about 200 to 400mA depending on current charge level of the battery.

If you have a Bench Power Supply you can inject 5V into the 5V test pad by the charger IC and observe for a current draw of between 200 and 400mA depending on the current charge level of the battery.

If you only have a multimeter, you can put the multimeter into Voltage DC mode and measure the battery voltage. Once you insert the charger cable the battery voltage should jump up by approximately 0.1V, and as you wait, the voltage should continue to slowly rise.

Although much less common, if all the above is ok yet you get no charging, its worth measuring the supporting components to make sure they are ok, and look for any obvious signs of damage or trace rot.

The diode D1 can be checked with a multimeter in diode mode, and should test OL one way and about 0.2V to 0.3V the other way.

If it is OL both ways or shorted both ways, it needs replacing.

Once removed before installing another, measure the pads where the diode installs with diode mode, to make sure the charger IC itself is not shorting those pins.

The next easy step is to measure all the resistors shown in the schematic.

For clarity that will involve putting the multimeter into resistance mode and measuring over each resistor (R21/22/23/25/26/27/28 and R47).

R23 is the same side as the charger IC, the rest are on the other side of the PCB right underneath the charger IC.

Each resistor should measure what it shows in the schematic, with the exception of R25 which on some boards in-circuit will measure around 5.4k instead of 18k. This is perfectly normal.

The same with R27/R28 measures around 6.3k instead of 10k on some boards. Again this is within spec and due to being in-circuit.

Although the capacitors are not requires for correct operation of the circuit (although it won't run fully correct), it is still worth checking them.

Place your multimeter into Diode Mode, and your red probe on ground, then with your black probe touch both sides of each capacitor (C28/29/30/31 and C68/71).

C28 and C71 are to the left of the charger IC, C29/30 are just above them, and C31/68 are on the other side underneath the charger IC.

One side should beep to ground (with the exception of C68, test this differently), the other side should show a voltage or OL. If both sides beep to ground, then it is likely faulty.

Here are the voltages of one side of the capacitors, read from a known working board.

If your voltage on a capacitor is well outside of this range or is OL when it should have a voltage, it could be faulty.

C28 = 1.54V C29 = OL C30 = OL C31 = 2.58V C71 = OL

We test C68 slightly different as it as no path to ground. Instead put your multimeter into Capacitor Mode and just probe over the capacitor directly.

You should get a reading of between 0.1uF and 0.3uF depending on the quality and accuracy of your multimeter.

If it reads 0L then it is likely faulty.

If all checks above run true and you are still not getting a charge, or perhaps something obviously like the charger IC getting hot / shorting, then your last step is possibly a faulty charger IC. If so you will need a donor board to hot swap the charger IC from.

If you battery is charging but you have no LED there are some basic checks to do.

Put your multimeter into diode mode and probe over the charge LED pins.

The charge LED is the bottom of the 3 LEDs on the left of the A/B buttons.

While you are there check all 3 LEDs work. Put your black probe on the right of the LED, and red probe on the left. The LED should light up.

The top LED is green (power on), the middle LED is red (low battery) and the bottom is charge (orange).

If all three do not light up I would suspect you are not probing correctly so check your multimeter is set in diode mode and your probes are the right way around.

If you find the charge LED does not light up, it is blown so replace it.

If the LED is good, measure the resistor R24 in resistance mode and that is measures around 1.1k.

R24 is located on the front of the board to the right of the A button, next to Q2 transistor.

If it measures OL or 0R then it is bad and needs replacing.

The Q2 transistor is responsible for passing the current from EXT_VIN (the pin 2 of the charger port where 5V enters the system) to the LED when the pin 7 of the charger IC sinks to ground.

The transistor has an internal pull-up resistor inside keeping the base pulled up to the 5V and keeping the LED turned off.

The quickest check is to put your multimeter into diode mode and put the red probe on the right single pin of the transistor, and the black probe on the left top and bottom pins of the transistor one at a time.

As you do this the charge LED should turn on, and your diode reading should be around 2.7V for both pins.

If your diode readings are correct, but your LED does not light up, its likely a damaged trace between the transistor and ground, or EXT_VIN, or the resistor R24. Check that in continuity mode.