Electronics > Repair

Kia car keyless entry battery draining

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boo9:
I have kia keyless entry what drains battery after 2 weeks.
There is a 46k resistance on +/- battery pads (when + MM probe on + battery pad), and 16k when probes are reversed.
I lifted C1, C8 caps and top tact switch and the resistance on +/- battery pads still there.
I suspect top left element (yellow arrow), looks like sc-70-5 outline from the measurements (2x1.3mm)

What elements that might be ?
Some folks suggested LDO regulator like http://www.s-manuals.com/pdf/datasheet/r/t/rt9013b_richtek.pdf  but IMO the pins dont fit into existing circuit.

when looking at attached picture

right top (+) connects to battery +  (EN pin in PDF)
right middle goes to KeeLoq chip (GND in PDF)
right bottom - ground (VIN in PDF)

left bottom not connected (VOUT in PDF)
left top - to circuit section left of main chip (NC in PDF)

Anybody has  any idea what that element that might be ?

cheers

SeanB:
Wild guess RF transistor. Try to reflow it, and clean the board properly. If you cannot get one use a donor remote to get a similar transistor.

boo9:
This is two sideded board with smd elements on both sides. Can I reflow one side safely ? will elments facing down not fall off during reflow ?

tautech:
Fixed a very similar after-market car key-fob for a mate recently.
One of a pair, but this one had exactly same symptons from new. Worked fine but it ate batteries.
In-circuit tests of all passives indicated they were all OK.
There is always multiple current paths for in-circuit tests, so one must use best judgement and experience.
Very carefull magnified examination revealed a tiny solder ball bridging a trace to a pin on an IC.
Flicked it out with a very pointed scalpel blade.
Fixed, no more problems.

Manufacturing QC had not even checked the current drain after assembly.  :palm:

wagon:
I've repaired literally hundreds of remotes.  Clean the board thoroughly.  Also, check (replace!) the two switches.  Contaminants get into the insides of the switches, causing enough current to flow to flatten the battery, but not transmit a signal.  Measure the voltage across the switch contacts without the switch being pressed : it should be the same across both switches.  If the measured voltage is too different, you have a bad switch.  Really, the voltage across the open switch contacts should be about equal to the battery voltage.

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