What to check first when only half my LED strip lights up
A cut in the wrong place. Cut intervals differ from product to product. Some tape is designed to be cut at frequent marked points, some at wider ones, and some products are built to be cut anywhere along their length. Check what your own item publishes rather than assuming (verify the cut interval marked on your tape before you trust a measurement). A cut landing short of a marked point can leave a pad too small to hold a connector, or open the circuit outright.
A connector that has let go. This is the most common of the four. A clamp joint that was seated well enough to work on day one can loosen with a knock, a temperature swing, or the weight of the cable pulling on it.
A damaged stretch. A crushed section under a cabinet edge, a corner folded rather than turned, or a length that has been pressed against a fixing screw can open a conductor while the top face still looks perfect.
A driver at its limit. If the run was recently extended, the supply may now be carrying more than it is rated for. That can show as protection cutting in, or as output sagging far enough that the tail of the run never reaches a level you can see.
Testing the joint and the cut
Reopen the connector at the boundary and look at what is actually touching. Pads should land squarely on the contacts, with no stray strand bridging the poles and no film of backing left across the copper.
Where the pad has been damaged or the cut was taken in the wrong place, the practical answer is to trim back to the next marked point and re-terminate. A solderless connector adapter rejoins the two halves without soldering when tape width and pad layout match, and the connectors and wires category lists what each item accepts (verify those compatibility details before ordering). If the tape itself is damaged rather than the joint, replacing the failed section covers the cut and splice properly.
When it is the supply rather than the strip
Meter across the driver's output terminals with the run connected, then with it disconnected. A supply that reads correctly with no load and drops away under load is being asked for too much.
Recheck the arithmetic. Multiply the watts per foot by the installed footage for every length on that supply, then require current headroom on top of the total (verify the published capacity of your driver and the current headroom guidance before you rely on either). If the number no longer fits, either move some of the run to a second supply or step up to a larger one from the power supply range. Keep strip and supply on the same voltage, 24V with 24V and 12V with 12V, and wire each length back to the driver as its own parallel pair rather than chaining one behind another.
Heat is part of this too. Drivers and strips both give off heat, and a supply running at its ceiling in a tight cavity has less margin than the same unit in open air.
