Start with your solder joints. The NASA Mars Perseverance Rover is the most complex kit we make — around twenty hours of building, and a great deal of soldering along the way. That is what makes it satisfying, and it is also why a Rover that does not work at the end is far more often a joint that has not quite taken than a faulty part.
This is not a comment on your soldering. On a build this size there are a lot of joints, and it only takes one.
What a good joint looks like
A small shiny cone, a little volcano shape, that completely covers the round pad and hugs the pin all the way round.
Solder coming through and covering the bottom of the pin, not just sitting on the top.
No solder bridging across to the pad next door, and no stray blobs left on the board.
A dull, lumpy joint, or one sitting on top of the pin like a ball without wetting the pad, wants reflowing. There are worked examples with photographs in My screen doesn’t work, what should I do?, and if you have bridged two pins together, I messed up a soldering joint and the solder is touching two pins. How do I fix it? walks through fixing it.
Then check the obvious things
Batteries. The Rover runs on six AA cells. Use fresh alkalines rather than rechargeables — rechargeables give 1.2 V instead of 1.5 V, which is not always enough for our kits to run properly, and there is more on that in Can I use rechargeable batteries in my DIY kit?. Check every cell is the right way round against the markings.
Connectors. Unplug and reseat each one, and check it is the right way round and pushed fully home against the build guide photographs.
The build guide. Compare your board against the photographs on the Mars Rover build guide page. It has over a hundred photos and it is the quickest way to spot a step that went astray.
If you are not sure why it is not working, message us here. Message us here, or email [email protected], with your order number, clear photos of both sides of the board, and a short video of what happens when you switch it on. Say whether you get any sign of life at all — an LED, a flicker, a sound — because that points somewhere quite different from complete silence. A person will go through it with you; you do not have to work it out alone.
If the Rover powers up but a servo will not move, that is covered separately in My Mars Rover’s servos or motors don’t move.