Outdoor flickering “candle” failure

[Hafcanadian]

I’m always having issues with my garden and patio LED lanterns, whether battery or solar powered. The one I’m trying to fix now is two AA powered. The lamp won’t come on at all, even though in the past it and its twin had funky switches. The switch seems okay this time, at least when I check continuity between its posts, and at one point I temporarily soldered in a larger switch that didn’t alter the result.

The board is cleaner than most that’ve been outside a lot, but the lamp won’t work. That said, if I set my LCR tweezers to “Diode” and put the tips across the lamp’s leads, the LED flashes (not flickers), so the LED seems okay. It’s flickering candle imitation must be controlled by a board component, or under normal voltage it may be the lamp’s built-in mode.

I note a “crystal”(?) can on the back of the board.

See photos and please advise what to check.

Thanks.

 

[ahsrabrifat]

Set your multimeter to DC current (mA), in series with the LED if you can.
Or, if not possible, put it across one leg and see if any measurable current is flowing.
Use diode mode on your multimeter to probe between its pins (usually Base, Collector, Emitter).
You should see ~0.6–0.7V drop B–E or B–C in one direction. If you get 0V in all directions, or OL in all, the transistor may be dead.

 

[schmitt trigger]

First of all, I applaud your attempt to fix this and avoid sending another piece of E-waste to the trash.
Do you see that black epoxy blob on the board in there? There is a naked chip below. It is the absolutely cheapest way to purchase and assemble a semiconductor, saving the manufacturer a few micro-dollars versus a SOIC or TSOP.
But the bond between the epoxy and board is NOT hermetically sealed. Humidity can, and definitely will ingress and damage the semiconductor. And it cannot be replaced.

I sincerely hope that there is something different and you can actually fix this device. But garden lights are usually a prime example of fecal-matter electronics devices.

 

[elfcurry]

First of all, I applaud your attempt to fix this and avoid sending another piece of E-waste to the trash.
Do you see that black epoxy blob on the board in there? There is a naked chip below. It is the absolutely cheapest way to purchase and assemble a semiconductor, saving the manufacturer a few micro-dollars versus a SOIC or TSOP.
But the bond between the epoxy and board is NOT hermetically sealed. Humidity can, and definitely will ingress and damage the semiconductor. And it cannot be replaced.

I sincerely hope that there is something different and you can actually fix this device. But garden lights are usually a prime example of fecal-matter electronics devices.

Would it help if such 'blobbed' cheapie boards were treated by covering the blob with varnish or some moisture-resistant sealant when new to make them last longer?

I'm assuming these cheap items work well enough when new and indoors but if used much outside will degrade.

 

[rjenkinsgb]

The blob is epoxy, which should be waterproof - at least initially.

I'd suspect failure is more likely to be from repeated thermal cycling, with different expansion in different materials eventually causing cracks.

If that damages the bond between epoxy and PCB, it could allow moisture in - but it may also result in the microscopic bond wires from the bare IC to the circuit board starting to detach.

Coating the entire board and wire connections in a slightly flexible varnish or resin would help prevent problems due to moisture, but you cannot do much about thermal stresses.