Hi, I am playing with some Christmas lights that stopped working because water got in to them. I have taken them apart to try to see how they work. They are a set of "Icicles" each of which has 18 leds in a row and they light in turn starting at the top and cascading to the bottom. They seem to be driven by a 6v DC source and each icicle is independent of the others i.e. it will work in isolation. There is an 8 pin surface mount chip that drives the leds and it is this I am trying to identify. It is labelled as 171009, with 72 below that. The PCB is marked U1 with 5072B. I can find no reference to any of these numbers.
I am interested in this chip because it seems to be able to drive 18 leds sequentially with only 4 control leads. Looking at the PCB, there are leds connected between the leads in a variety of combinations and polarities. I have tried to measure waveforms with my PC Scope but the leds behave differently when I connect the leads and the readings do not make sense. I suspect that the scope has too low an input impedence.
Has anyone any idea as to what chip this is using?
Thanks.

 

Good chance it is a OEM number!
Max.

 

I have tried to measure waveforms with my PC Scope but the leds behave differently when I connect the leads and the readings do not make sense. I suspect that the scope has too low an input impedence.

Most scope have ~1MΩ input impedence. Try putting a multi kΩ or MΩ resistor in series with your probe. Most likely it is a preprogrammed IC to control the lighting sequences.

 

I thought it might be a custom chip. I also wondered if the leds are not ordinary ones but have some kind of addressability.