Newbie Needs Help Fixing Simple(?) PCB for Four Christmas Tree Lights

Thread Starter

rennervision

Joined May 19, 2022
6
Hello. I was hoping someone could help me diagnose and fix a little PCB inside a collectible bottle that lights up with four Christmas tree lights. (If it wasn't for the outrageous eBay prices, I would just buy another.)

Photo #1 shows the internal wiring. From what I've gathered using my multimeter, the lighting (when operating correctly) worked like this: The power comes from three AAA batteries inside a battery holder attached to the PCB. The circuit to the lights is actually complete when the silver button attached to two green wires is NOT pressed. However, if I press & release the button, this interrupts the circuit, which then somehow causes the four Christmas tree lights to power on for 30 seconds. If I were to change the batteries, this would also cause an interruption of the circuit and, likewise, the lights would power on for 30 seconds.

1.jpg
Photo #2 shows the underside of the PCB. There are two transistors and four resistors. Half are used for the positive line to the lights, and the other half for the negative line returning to the battery pack. The negative transistor is marked 58050 D.016 and there are no markings on the positive transistor.

2.jpg
Photo #3 is my best attempt to explain how the electricity flows. (My apologies as I'm not very knowledgeable to draw up a professional-looking schematic.) From what I've discovered, the positive flow (depicted in red) starts off with 4.5v from where the batteries' positive line connects to the PCB and branches off in two paths. Likewise, negative (depicted in black) is returned to the batteries from two separate paths as well. I've noted the voltage in other spots on the PCB as it sometimes changes. Curiously, I measure 0 volts in the bottom right corner. Not sure if this is working as designed, but it remains 0 volts after I press the button now to test. Also worth noting, I drew a green line in the bottom right corner between two solder points. When I physically connect these two with metal, the bulbs light up. (But they only stay on as long as the connection is maintained. There is no "30 second timer" by doing this, and since I'd have to physically press the silver button to break the connection, this method will quickly drain the batteries.)

3.jpg
So due to my limited electronic knowledge I have three questions:

1. How does this board with two transistors and four resistors somehow simulates a 30-second timer to light the bulbs?
2. What is that black dome in the middle of the board? (Is it doing something to create the lighting effect?)
3. Is there a way to fix this so it's running properly again?

Thanks so much for reading!
 

peterdeco

Joined Oct 8, 2019
481
Welcome to the forum. The black dome has an IC chip inside and is the "brain" that controls the function and timing of the lights. I hate to say it, but it is usually the cause of malfunction, is not repairable or replaceable.
 

Thread Starter

rennervision

Joined May 19, 2022
6
After reflecting on this some more, I'm wondering if it's possible to build a circuit that essentially does the same thing? I noticed this reddit post reads like someone was trying to build something similar to what I had complete with IC timer:

https://www.reddit.com/r/AskElectronics/comments/3o09cr
Problem is I'm out of my level of expertise. I would either need very detailed instructions, or I would be willing to pay any capable person offering to build it. Whatever they think is a fair price for their time and parts I'm sure will be agreeable (I won't be a cheapskate), and then I could solder on the on/off button and battery holder. Or perhaps someone could recommend a service out there that could build this?

The PCB wouldn't need to be the exact same size as the tiny original. It would just need to be smaller than the 3 AA battery holder so it fits inside the prop.
 

Thread Starter

rennervision

Joined May 19, 2022
6
Yes. Based on what I read, it's a normally closed push button. The switch makes electrical contact with the circuit in it's default state. When the circuit is opened (by pressing the button or changing the batteries) this interruption triggers the lights to power on for 30 seconds after the circuit is closed again. (The button is on a spring so it pops back to its default state immediately after you press it.) So from what I gathered from peterdeco's post, there's an IC chip that makes this happen with the lights.
 

MrSalts

Joined Apr 2, 2020
1,762
Yes. Based on what I read, it's a normally closed push button. The switch makes electrical contact with the circuit in it's default state. When the circuit is opened (by pressing the button or changing the batteries) this interruption triggers the lights to power on for 30 seconds after the circuit is closed again. (The button is on a spring so it pops back to its default state immediately after you press it.) So from what I gathered from peterdeco's post, there's an IC chip that makes this happen with the lights.
Check your DM above.
 

Thread Starter

rennervision

Joined May 19, 2022
6
I just wanted to provide an update and say MrSalts is a godsend. Within a matter of days after his reply, he had a brand new PCB for me with the exact same dimensions, screw holes that line up perfectly, and ready to ship. When it arrived, he provided tech support (faster and better than any company I've ever dealt with!) and - when things weren't quite working like they should - actually had an additional replacement board ready about a day later. The new board arrived today and it works like a dream.

I'm grateful for this site and helpful folks making the world a bit happier. (I think every little bit helps these days.) MrSalts - a very big THANK YOU!
 
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