Faulty circuit board. Looking for help diagnosing and fixing

Hi, i am hoping I could find someone at VHS to help me diagnose and fix a little circuit board. It’s for a little Christmas tree with LEDs. I have checked the string of lights they are okay. I have done some continuity testing on the board but I can’t isolated the component that is failing. I am really hoping there might be someone in the VHS community that can help me with this, maybe it needs to be put in a reflow oven?

I look forward to hearing your responses.


Is there supposed to be a connection between v -and the battery terminal on the left ? It looks heavily corroded. I assume it supposed to make contact but it looks eaten away or maybe it’s just dull copper.

Is it double sided pcb? Photo of other side?

Is the switch working?

Have you tried meowing at it?

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Yes there was a lot of battery corrosion when I took it out of storage, I managed to clean it up with some vinegar on a Q-tip. Once I cleaned up the corrosion the Christmas tree worked for a while, and it looked beautiful, then failed :frowning: maybe some of the vinegar seeped onto the PCB which probably advanced the corrosion.

I have managed to detect continuity from the V- all the way to the 8pin IC. Yes the switch is working the continuity test told me so.

I know I lack the experience to know what to do next. Maybe my next approach should be to put it in a reflow oven? but I have no idea how that even works.

Reflow probably won’t work. It’s got so little chips you probably won’t have much luck identifying anything. Could probably wash it and let it dry or use hair dryer.

L1 and l2. One wire is disconnected. Did you flip polarity?

Yes, L1 & L2 connect to the LED lights, I disconnected L1 when I was doing the continuity test, but I know the string of LED lights work.

I think you’re probably out of luck. That is probably a custom programmed chip. A replacement isn’t available usually. Unless that’s a 555 but a crystal is usually for a microcontroller.

The 5 pin chip is probably a MOSFET. Maybe shorted?

Like there isn’t enough component there to troubleshoot kinda.

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The reflow oven isn’t likely to help. It’s good for when you suspect micro cracks in the solder on a board with lots of small components.

In your case there are few components, and some major damage to the PCB. I would suspect broken traces. If you can find the problem you can solder a bit of wire to bridge the breakage.

I suppose it’s possible that while cleaning it, you left some liquid that created a short when you powered it up. With vinegar that doesn’t seem too likely though.

I would get this on the bench at VHS, power it up with a current-limited supply, probe around with a multimeter or scope. It’s likely fixable and a perfect project to learn some basic electronics troubleshooting.

Depending on how much time you want to invest you could determine how the LEDs are driven and then make an Arduino based controller to replicate the broken one…

I suspect the LED is of the 2 wire led string variety but we would need more info…

There is a lot for me to learn with this project. I might try replicating it with an arduino.
Thanks for your responses.

Does it just blink? Use 555 or two transistors.

It has about 4 different modes. Blinks, multi colors, alternate flashing etc.