GE / Jasco z-wave switch failure (internal LNK304 power supply pulsing)

Thread Starter

Lifeisfun

Joined Feb 17, 2023
92
Hi folks,
I got tremendous help before her so I like to ask for more help again.

I got couple zw4005 switches that failed.
This is fairly common problem and capacitor replacement usually fixes the problem but not all the time.
Usually they start clicking on and off and stop responding to anything. There is YT video about this issue.


switch power.jpeg

Symptom is that the LNK304 based power supply in the switch will not start up and it's pulsing instead.
Common culprit is the c3 cap 10uF but even after I replaced all of them, the switch still doesn't work properly.
It powers up fine but within several minutes it starts turning on/off or sometimes the relay shivers and then gets quiet.
If I unplug it and plug it back in later all this repeats it self.
When I desolder those 2 boards a part looks like the power supply is working fine without the 3.3V load.
Problem is probably not caused by the zwave board itself since when I inject 3.3V to the controller board it works perfect. 3.3V/30mA
The 12V relay is also fine.
Tested for short on the board, tested ceramic cap, all looks fine.
Strange things I found:
On one of these switches had the transistor that controls the relay shorted (located right by the relay coils terminals)
Also when initially power is applied, the area around pin4 (D) of the chip towards the relay coil terminal gets hot ( isopropyl evaporates bubbling,
also tested with thermal camera) but cools down within seconds and holds 27C steady there after.

Any ideas?
Thanks
EDIT: Thought I found solution by replacing the chip but the problem is back :(


PXL_20231231_125535063.jpgPXL_20231231_125553466.jpgXinf_231231_093651_962.jpgXinf_231231_093703_727.jpgXinf_231231_093730_618.jpg
 
Last edited:

Thread Starter

Lifeisfun

Joined Feb 17, 2023
92
Happy to report that the problem is now solved 100%
Replaced once again the transistor that controls the relay, and it's working perfect now.
 
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