These are two unrelated conditions that look identical from the desktop. The lock tab on a full-size SD card is a passive slider the reader socket senses and the host chooses to honor, and nothing inside the card enforces it. A controller that has latched itself read-only is a firmware state the device enforces from the inside, and that one is your signal to stop writing and image the device.
How an SD Card Lock Tab Works
The slider rides in a notch molded into the edge of the card body and connects to nothing electrically. It is a hint, not a lock. A small mechanical switch inside the reader socket feels where that slider sits, the driver reads the switch, and the operating system decides on its own whether to issue writes.
A microSD card sitting in a full-size adapter is the case people misread most often. The microSD card has no tab of its own; the adapter carries one. Toggling it moves a switch that belongs to a piece of plastic, so a worn or sticky adapter slider write-protects a healthy card, and a different adapter clears the same card.
A card the host refuses to write to is normally still fully readable, and reading is all a recovery needs. Copy the files off with a reader you trust, verify they open, and you are finished without a lab and without a bill. We would rather tell you that than open a case that did not need opening, and if you ship it anyway and it reads clean, there is no diagnostic fee.
Controller-Enforced Read-Only Mode
The second state comes from inside the device. A flash controller maps the logical sectors your computer asks for onto physical NAND pages through its Flash Translation Layer, and refusing writes is one of the protective states it falls into when it can no longer trust that map. Power dropping partway through a mapping-table update leaves metadata the controller cannot validate on the next boot. Wear arrives at the same state from the other direction, since a controller with no healthy blocks left to write into keeps serving reads while writes stop. The same latch appears in solid-state drive recovery for the same reason: firmware would rather refuse a write than damage the map that makes your files addressable.
Image it now and work from the image. A read-only device answers reads while the latch holds, so a full sector-level image is available, and every later question about the file system gets answered against a copy instead of against the failing part. Do not run a vendor or mass-production utility to clear the read-only condition. Those tools re-initialize a device rather than repair one, re-initialization rewrites the translator tables your files are addressed through, and the latch is what has been keeping the device out of that state.
Where Each State Stops Being a Two-Minute Fix
On the lock-tab side, the tab is a red herring the moment the card does anything else wrong. A card that refuses writes and also throws read errors, reports a capacity it never had, or mounts as RAW has a fault behind the slider, in the controller or in the NAND, and those are the cards that need lab work rather than a second reader.
On the controller side, the read-only path lasts as long as the device keeps enumerating. Once it stops registering with the host, there is no block device left for software to read, and no scanning tool reaches the cells through a controller that never answers. The work escalates to reading the NAND off the board directly, which is the chip-off and monolith path.
