12VAC garden LED lights, burnt out components, anyone skilled enough to guess what they were?

Thread Starter

flappa

Joined May 8, 2016
6
Hi
Hoping someone can help. I have attached a diagram of the circuit inside a rather expensive stainless steel garden light. So it's worth trying to fix it.
It was damaged by an over voltage and two components on the internal circuit board were burnt out.

What appears to be a 1w resistor and a very small diode (1N914 / 1N4148 size). The transistor cracked open but I could identify it as per the diagram.

It's a 12v AC input light fitting with about 30leds. The internal circuit board converts the AC to 5V DC

Any ideas anyone?
 

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bertus

Joined Apr 5, 2008
20,651
Hello,

It looks like you switched pinnames in your schematic.
The correct pins are these:

MJE13003_pinout.png

The diode in the circuit will likely be a zenerdiode of about 5.6 Volts

Bertus
 

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Thread Starter

flappa

Joined May 8, 2016
6
Hi Bertus,

The Transistor is a TO 92 package and it's the 'B' > 13003B. apparently from online spec sheet it's as per my diagram.
I have uploaded a picture of the PCB. The Diode is on the other side.

Any guesses on the resistor? I'm only assuming the output is 5v DC. And it's exactly 30 Superbright LEDS

Thanks
Frank
 

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bertus

Joined Apr 5, 2008
20,651
Hello,

Is it possible to post a photo of the top and bottom of the led board?
Then we can see how the leds are connected and estimate the needed voltage.

Bertus
 

Thread Starter

flappa

Joined May 8, 2016
6
Hi Bertus,

Not possible, it's silicone sealed into the head of the tube fitting out of reach. It took some careful and painful work getting the PCB out from the underside without damaging the rest. I see what you are getting at. I'm thinking I'll have to pull apart another working unit to determine the resistor value and read the output voltage. What I was trying to avoid, but I may have no choice?

Frank
 

bertus

Joined Apr 5, 2008
20,651
Hello,

On the powerboard there is a connector to the leds.
Do you have a adjustable powersupply?
Watch the polarity, it is given at the plug on the powerboard.
If so, you could start at a low voltage and turn the voltage up, until the leds are at the brightness you are used to.
The reached voltage must be made with the powerboard.

Bertus
 

Thread Starter

flappa

Joined May 8, 2016
6
Hi, I'll get my hands on an adjustable power supply and see how I go...thanks Bertus for your advice so far.
It may be a couple of days before I can attempt it.




+10 GMT
 

takao21203

Joined Apr 28, 2012
3,695
particulary bad circuit

Use a stepdown dcdc module, increase the voltage carefully.
You could measure the current, it will be wrong with DMM a bit.
If it is normal LEDs 15mA or so is enough.

throw away the bad PCB...
 

Thread Starter

flappa

Joined May 8, 2016
6
Hi,

So I have identified the Resistor to be 150ohm and the output is actually 12vDC (I resorted into pulling apart a working unit)
So can I assume the diode is a Zener of 12volts?

Frank
 

Thread Starter

flappa

Joined May 8, 2016
6
Hi,

The input is specified as 12v AC. The output from the working circuit is 12v DC.
I have used a 12v Zener and now all is working fine on the repaired unit. I ended up using a BD639 to replace the transistor.
Brightness matches the working unit.
I'll make sure I don't feed in the incorrect voltage next time!!

Thanks for all the suggestions and discussions of help folks.

Problem solved.

Frank
 
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