2.7v Voltage Clamp

[sleemanj]

The first image shows the whole board and the second shows the unpopulated pads next to the trim pot.  Compare that to the image from the eBay listing that shows the exact same angle as my second photo (looking at the corner containing the Out+ pad).

What you have there is a LM2596 based buck converter (you can read the markings on the chip to confirm), it looks complete at least (erp, maybe not, see next post), but if you bought an LM2577 auto step-up/down converter then that's not what you got.

What you have is a step-down (buck) board only, input must be higher than output. 

You may have to give the pot a lot of turns to get it in range before it starts stepping down, these are 20 turn potentiometers, just dial it all the way in one direction until it clicks, and if still nothing, go in the other direction.

These are the typical specs:
Input: 4 to 35v
Output: 1.25 to 30v
Maximum output power: 12w without heatsink, 20w if you slap a nice heatsink on the bottom of the board (not included)
Output current: 2 Amp but remember the power limit above, if using a heatsink you can probably push this to 2.5A or 3A peak
Ripple: 30mV

[sleemanj]

Oh that missing component I didn't notice, looks like it may have been an SMD resistor which has been knocked off (have a look in the mailing bag it came in).  If you want to try and get it working, you may find it's actually a 0 ohm resistor (aka, jumper), I have a bunch of buck boards which use a 0 Ohm in that position (but the board design is slightly different). 

[mariush]

See if it's in series with potentiometer. It might be a resistors chosen in such a way so that along with the trimpot the lowest you could go would be 1.25v.

[wilheldp]

Thanks for the suggestions, guys.  I finally got around to tinkering with this again tonight.  It is indeed a LM2596 controller.  That isn't necessarily a bad thing, because I don't really need to boost (although it would be nice in low-sunlight conditions).  Regardless, I'm going to complain to the eBay seller and see if they'll send me what I actually ordered.

I also tried turning the hell out of the pot in both directions.  I swear, I turned it at least 100 times in both directions, and it never once clicked or produced a voltage on the output.  I'll try to add a low value resistor to the unpopulated pads tomorrow and see if that changes anything.  BTW, throughout testing, I had roughly 2.1v on the input to the board.

EDIT:  I just realized that the minimum input voltage is 3v on the board.  But still, there should be some sort of indicator that the trim pot has reached it's upper or lower limit after a certain number of turns, no?

[sleemanj]

EDIT:  I just realized that the minimum input voltage is 3v on the board.  But still, there should be some sort of indicator that the trim pot has reached it's upper or lower limit after a certain number of turns, no?

They usually sort of tick per revolution if you turn past the limit.  But you got a multimeter right, measure it, turn it some, measure it again,turn it the other way, measure it again

Assume you paid by paypal, if the seller doesn't come to the party, dispute the transaction.