Weird components

[TheGenesis]

Hi everyone,

my chinese RC-Charger died while it was discharging my lipos (for storage) with a rate of 0,8a @12v.
Seems that the internal powersupply has failed on the secondary side.
I suspect 2 components but i have trouble to identify and measure them.

First component that makes me nervous is marked with K100A10N1 ... looks like a Mosfet but google only finds a thoshiba with an additional "T" in the part number.
On aliexpress i found some similar looking chips described as "100V Silicon N-kanal MOS". I'd rather like to put some known branded chips in the thing because it died just after 20h.

The second component looks like and is identified as a capacitor using my chinese component tester. But why on earth my multimeter is not able of measuring the resistance of the thing and shows open circuit? And why does it have an ESR of 18 Ohms? Is this because it has failed or could this be normal?

On the PCB, the "capacitor" is marked as Y1 ... according to wikipedia this should be an crystal or oscillator ... i'm totally confused.

Can someone bring light into my darkness? 

Thanks in advance!

[Jwillis]

First component is indeed a MOSFET .  https://www.mouser.com/datasheet/2/408/TK100A10N1_datasheet_en_20140128-1915930.pdf  AKA  K100A10N1
Capacitors will show a very high resistance "open circuit" when charged . The ohm meter applies a small voltage to do it's measurement . Therefore charging the capacitor.
The tester will show the correct or very close value of the capacitor.
As for the designation I don't have an explanation . Unless someone else has seen a crystal that looks like what your describing. 

[Manul]

There is such part as toshiba TK100A10N1 100V mosfet. The capacitors is probably marked like this, because it is an Y safety capacitor. It is probably crossing isolation barrier in the circuit? The ESR measured is plausible, we dont know measurement frequency. Also such meter is expected to be quite off in some cases. Capacitor should show open circuit while resistance measured, this is normal.

[TheGenesis]

Ok thanks. Yes, the capacitor inded is crossing the isolation barrier. It is connecting the mosfet on the primary side of the transformer with the mosfet on the secondary.
I'll go and replace the mosfet while leaving the capacitor alone.
But shouldn't the capacitor shows an increasing ohm value while charging (like the electronlytics)?

[Manul]

But shouldn't the capacitor shows an increasing ohm value while charging (like the electronlytics)?

The value of capacitor is just ~2.3nF, such capacitance charges up much faster then the meter can react. Or if the meter could react, you would not be fast enough to see with your eyes. Increasing resistance is observed on much bigger capacitors, like 1000 - 10,000 times bigger and up.

[TheGenesis]

Just want to give an update.

I replaced the mosfet and resoldered the capacitator and the charger is now working like a charm.

Thanks for the help guys!