Hi everyone, I am a newby

I studied electronics at GCSE and A-Level but didnt really remember to much theoretical stuff and now I have a problem I am sure I can overcome with some help!

I have a set of LED christmas lights that run on UK Mains voltage (not transformered) and they have a flasher unit on but I want to 'by-pass' this and make the set fully static.

Here is photos of the board:


http://i250.photobucket.com/albums/g...8/100_2271.jpg

The input wires are on the top left hand corner.


http://i250.photobucket.com/albums/g...8/100_2271.jpg

I hope you can help me!

Many thanks

Karl Beetson

 

no photo..........

 

is it ok now?

 

How many branches and how many LEDs in each chain?

 

2 wires in from the plug and 5 wires out.

The transistors are: PCR406J
That any help?

 

would it work if I:

connect jumpers between the transistor leads closest to the end of the board. This can be done with a single wire that connects straight across those 8 pads in a row.

 

I do not know how expensive this set is, or what kind of loss it would be for you if they were damaged...Common sense, or at least common electronic sense, tells me that two of your wires are your LINE and Neutral inputs, while the other 5 sets of wires represents 4 branches with a common return...THUS 4 transistors individually switchig those branches.

I would certainly think, judging by the two rows of solder points for the 4 transistors, that the bottom row on the picture is either the base or gate, and the other row of 8 solder points are the e-c or s-d junctions. Each base/gate is connected to the IC that is driving them.

You certainly will be turning them on full if you jumper the e-c or s-d junctions (not sure if these or bjts or fets)...which will swicth the lights on.

It appears to me that your line voltage is being rectified by the diode bridge to drive the IC, and the LEDs with no regulation and minimal filtering. I haven't reversed engineered the circuit but you should probably ceck the voltage from common to each transistor leg, measure the voltage drop across the junction and the supply voltage, just to be sure that voltage drop doesn't need to be accounted for, imho.

I would jumper 'em just for kicks and not worry about smoke, if it were me

 

hey thanks for your reply,

I am noway confident enough to be probing with a multimeter as its such a high voltage 240v....dont want to electrocute myself.

So do you feel confident that if I solder as in the new attached picture that it will be static and also safe...I dont want any electrical fires etc

Attached Thumbnails

 

 

If they were designed to flash causing them to be steady on all the time may likely destroy them, the unit, or your house... Buy a proper unit.

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Its a MULTI FUNCTION flasher unit. 1 of the functions is static.... but everytime you power off it doesnt remember the last setting used and I wont have access to the push button to go change it...

So if the set can go static whats the difference of "hot-wiring" it?

 

Yes, I do believe a wire soldered straight across all the emitter and collector pins will have the LEDs full on.

And if the unit originally had a full on mode, I see no problem.

But the advice given by the other poster is sage when you consider how much a set of Christmas lights really cost vs a burned down home. Just depends on how confident YOU are with doing it. I wouldn't worry myself, if that means anything.

 

thank you =)

 

Bridging the transistors will probably work but there may be a problem if the LEDs are multiplexed. A better solution would be to solder a resistor between C and E to limit the current. Without knowing more about the circuit it is hard to make a good guess at a value.

Mike.

 

Depends on how the string is wired, bypassing the transistors is going to give you an extra .6 volts to the LED chains. Also since there's no way to tell as I'm assuming that little vertical board is blobbed IC, it may have been PWM'ing the LED's even when it was in it's static appearing state. There doesn't appear to be any resistors in line with the LED's, something must be regulating the current, if not then it's really a horribly designed circuit.

Just trying to understand the circuit more, you said this was powered directly by mains? Cause what you have there is a simple bridge rectifier with a capacitor filter. That would mean that the blobbed IC is dropping the voltage and must have current limit resistors for the transistor bases? One of those resistors is connected to the IC, and I can't tell what the other one is for. All I can say is go ahead and short the transistors out of the picture and cross your fingers. I sure hope there's an inline fuse on the power cable.

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The "transistors" are SCRs', if it matters.

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de KI6RWX