Philips Razor Circuit Diagnosis (Disassembled)

[gathermewool]

I disassembled the razor because the battery was dead and the charger showed bad battery. I force charger the battery for five min at 4VDC using a bench-top power supply, which resulted in around 0.7A. The battery now shows 3.477VDC. I get the same voltage on the other side of the board, at the soldered locations.

The issue is that when I check the tabs that actually connect to the charger I get nothing at all. I had to actually pull the cover off and connect alligator clips to the tabs directly attached to the battery to force a charge.

So, the large solder on each side of the board shows battery voltage (it’s soldered through the board to the tabs directly connected to each side of the battery. The solder on the left side of the pic (reverse side of the board to the battery), near the button, is positive. On the opposite side, the large solder AND the smaller bits that are labeled pos and neg also show full voltage. Ie, positive full voltage is shown with positive lead on the left solder and the negative lead on any of the three on the other side.

What the heck am I missing?

 

[ka9mnx]

There may be reverse polarity protection diodes between the charger connection and the battery. One of these diodes may have failed open.

 

[Exit32]

It's likely there's some fairly sophisticated battery-charger circuitry between the pins into which the charger plugs and the battery itself. This is to ensure that the lithium cell is not overcharged by the external charger if you leave it connected for an extended period.

If your shaver's charger itself is working correctly, then your problem is likely with the battery-charger circuitry.

 

[gathermewool]

There may be reverse polarity protection diodes between the charger connection and the battery. One of these diodes may have failed open.

when I check either way it shows pod and neg, if that matters. I would think a diode would only show voltage in one direction.

 

[gathermewool]

It's likely there's some fairly sophisticated battery-charger circuitry between the pins into which the charger plugs and the battery itself. This is to ensure that the lithium cell is not overcharged by the external charger if you leave it connected for an extended period.

If your shaver's charger itself is working correctly, then your problem is likely with the battery-charger circuitry.

My first thought was a battery charging circuit safety feature that prevents charging if the voltage drops too low. 0.9VDC is pretty low. I monitored the temp and stood well away while charging it.

It didn’t heat up and still shows voltage. I’m just not sure how to reset the safety feature. I’d have to break the tabs off and then solder them back on if thats what’s required to reset the system. I’ve never soldered to a battery before, but I could manage. I’d just rather not have to do that.