I am trying to repair an AEG AL1218 (Ni-Cd, NiMH, Li-Ion) cordless drill battery charger. The part number on the PCB is: 260019004/05/06



The switched-mode power supply isn't working. I have by chance identified an open circuit 4.3M Ohm resistor (R6) which connects to a 5 pin IC (U1) that is attached to a large metal heat sink:



The other end of the resistor connects to another 4.3M Ohm resistor in series, which is connected to one of the primary bridge rectifier diode's cathode.

I was measuring voltages on the PCB with a multimeter and happened to touch the probes between the IC pin (which has the open circuit resistor attached) and a coil pin on the primary side. The power supply started working! I assume the high resistance of the meter was enough to take the place of the open-circuit resistor?

What would have caused the resistor to fail and what purpose does it have to operate that 5 pin IC? Could I substitute it with 2x 2.2M Ohm resistors?

Thanks.

 

We need a closeup of the five pin IC, and it's part number. Can you get that?

 

I am trying to repair an AEG AL1218 (Ni-Cd, NiMH, Li-Ion) cordless drill battery charger. The part number on the PCB is: 260019004/05/06

View attachment 98425

The switched-mode power supply isn't working. I have by chance identified an open circuit 4.3M Ohm resistor (R6) which connects to a 5 pin IC (U1) that is attached to a large metal heat sink:

View attachment 98424

The other end of the resistor connects to another 4.3M Ohm resistor in series, which is connected to one of the primary bridge rectifier diode's cathode.

I was measuring voltages on the PCB with a multimeter and happened to touch the probes between the IC pin (which has the open circuit resistor attached) and a coil pin on the primary side. The power supply started working! I assume the high resistance of the meter was enough to take the place of the open-circuit resistor?

What would have caused the resistor to fail and what purpose does it have to operate that 5 pin IC? Could I substitute it with 2x 2.2M Ohm resistors?

Thanks.

These things get thrown around a lot. Are you sure it is the resistor that has gone bad or could it be a solder connection or a copper trace? You can touch a solder tip to the pads to reflow the solder to see if that fixes the issue.

Otherwise, yes, 2 x 2.2M ohm will be the same (and within tolerance in most cases).

 

Here is a close-up photo of the IC - unfortunately, the transformer is in the way so I cannot remove the screw:



I have desoldered the resistor and it is definitely open circuit. The colour coding on the resistor is (Yellow Orange Green Gold).

Looking at the IC closer, it seems as though it has 6 pins?

 

Some SMPS use 2 resistors in series around that value to kick start the powersupply. Just replace them & see if it works. Yes you could use 2x 2.2M resistors in series if that's all you have.