Rewiring christmaslights

[Fristi]

Hello,

I have christmaslights with 7 preprogrammed cycles. I only need the last one, which is the solid light but to get to this I have to push it 7 times every day because there is no memory. It uses 24v. Is their a way to just connect the wires to get the solid light?

 

[stewartrossinv]

The four power transistors on the lowest part of the PC will provide the current source for each of the LED groups, driven in turn by the smaller transistors immediately behind the power transistors. These in turn will connect to the dedicated controller, which is not something that can be bypassed.

Attempting to drive the LEDs directly by some means that bypasses their dedicated (very simple!) drive circuitry is just going to lead to disappointment. If the four groups are disconnected and wired up outside of the dedicated controller, how would the OP do so? The max current for the LED groups is unknown, their colour or positional grouping is unknown, whether the groups are in series or parallel or a combination of both is unknown and so on. I'm all for experimentation, but in this case I think a good outcome is very, very unlikely.

 

[DPG]

The four power transistors on the lowest part of the PC will provide the current source for each of the LED groups, driven in turn by the smaller transistors immediately behind the power transistors. These in turn will connect to the dedicated controller, which is not something that can be bypassed.

Attempting to drive the LEDs directly by some means that bypasses their dedicated (very simple!) drive circuitry is just going to lead to disappointment. If the four groups are disconnected and wired up outside of the dedicated controller, how would the OP do so? The max current for the LED groups is unknown, their colour or positional grouping is unknown, whether the groups are in series or parallel or a combination of both is unknown and so on. I'm all for experimentation, but in this case I think a good outcome is very, very unlikely.

Agree, it will likely be beyond the OPs abilities.

 

[littlespark]

It might be worth measuring the voltage coming in on AC, and the voltage going out on each of the 4 channels... (between 1 and C, 2 and C etc) when the program chip is set to static on.

If its the same, then just cut the controller out and replace with a joint.

Best just to buy a new static string of that’s what you want, and use this one elsewhere.
years ago, I decided to turn an old static light string, the really old type with with dozens of lamps in series.
I “acquired” a flasher unit from an amber roadworks light... a 12v relay from car spotlights and voila!

worked ok, if you could stand the click click click of the relay

 

[freddo]

It would be useful to see the print side of the circuit board but you probably just need to twist the 4 smaller transistors 1 turn, and put the lid back on! Job done.

 

[stewartrossinv]

It might be worth measuring the voltage coming in on AC, and the voltage going out on each of the 4 channels... (between 1 and C, 2 and C etc) when the program chip is set to static on.

If its the same, then just cut the controller out and replace with a joint.

Sorry Little Spark - this is just not going to work. LEDs are not like filament lamps; they are current-driven DC semiconductors which have to be driven from a current-limited source (approximated in simple DC single-LED circuits by a series resistor to provide a relatively constant current of, say 30mA at their voltage drop of 2.5V or thereby). LEDs are particularly sensitive to reverse-drive voltages and accordingly are never driven from AC voltage sources. The outcome will be for all of them to go pop simultaneously.

Seriously, don't try it.

 

[DPG]

Sorry Little Spark - this is just not going to work. LEDs are not like filament lamps; they are current-driven DC semiconductors which have to be driven from a current-limited source (approximated in simple DC single-LED circuits by a series resistor to provide a relatively constant current of, say 30mA at their voltage drop of 2.5V or thereby). LEDs are particularly sensitive to reverse-drive voltages and accordingly are never driven from AC voltage sources. The outcome will be for all of them to go pop simultaneously.

Seriously, don't try it.

And it may be a straight DC output, or PWM (which is more likely).

In reality, the right value of current limiting resistor (1 per output) will probably do it.

 

[stewartrossinv]

In reality, the right value of current limiting resistor (1 per output) will probably do it.

The chunky output driver transistors shown in the OP's post would suggest a max output driver current of perhaps around 200-300 mA for each group - there's no heat sinks attached to the power transistors, so it's not likely to be above that (as otherwise the output transistors would overheat, even though we're only talking about, say, 0.75W dissipation for each group). The four groups would be I guess around 3W dissipation in total if connected in parallel and not individually - so the OP would need to use, say, a 5W wirewound resistor of a suitable value, though what that value may be is somewhat moot. It really would be simpler just to buy new lights...