Card failures alarm people more than drive failures do, partly because what is on them cannot be shot again and partly because the warning is worded as though the pictures have already gone. In the overwhelming majority of cases they have not moved at all.
A memory card is three things stacked together. There are the NAND flash dies, where the photographs physically live as charge held in cells. There is a controller, a small processor that decides which physical block each logical address corresponds to, spreads writes around so no one area wears out first, and hides failed blocks from view. And there is a file system, usually FAT32 on smaller cards or exFAT on larger ones, which is nothing more than a directory listing recording the name, size and starting block of each file.
That directory is a tiny fraction of the card — a few hundred kilobytes describing tens of gigabytes of pictures. It is also the part that gets damaged, because it is rewritten every single time a frame is saved or deleted, while the photographs themselves are written once and left alone. Pull the card out mid-write, run the battery flat during a burst, or let the contacts go intermittent, and the directory is what tears. The computer then finds no usable file system, concludes there is nothing on the card worth reading, and offers to set one up for you. Not one image has been touched at that point.
Everything that turns a full recovery into a partial one happens in the next thirty seconds. Accept the format and a clean, empty directory is laid over the damaged one, which removes the fastest route back and leaves only the slower one. Put the card back in the camera to try a test shot and new data is written into blocks that the controller considers free — and because of wear levelling you have no say whatsoever in which physical blocks those are, so a single frame can land anywhere. Neither action has an undo and neither is reversible by anyone at any price.
So the most useful thing you can do with a misbehaving card is the thing that feels least like doing something. Eject it, put it somewhere safe, and stop. Until a format or a fresh write happens, every photograph is sitting in the flash exactly where the camera left it, and the odds are as good as they will ever be.
A few unglamorous explanations account for a surprising share of calls. Full-size SD cards carry a sliding write-protect tab on one edge; it gets nudged into the locked position inside a bag, and a locked card reads erratically or refuses outright. Contacts pick up skin oil and grit, which a dry cloth handles at no cost. And readers themselves cause more of this than anyone credits. The spring contacts inside a cheap adapter lose tension after a few hundred insertions, a laptop slot that has taken thousands of cards is no better, and either will produce read errors on media that a decent powered reader handles without a murmur. Test the card in a different reader on a different computer before you conclude anything about the card itself.
One more check is worth running, because it explains a whole category of failures that look like corruption and are not. Cards bought cheaply from online marketplaces are frequently counterfeit, with the controller reprogrammed to report a capacity the flash does not have. A card sold as 512 GB may hold 32 GB; it accepts everything you shoot, discards or wraps around the surplus, and appears healthy right up to the moment you try to read the later files. If the card was suspiciously cheap and the failures started once it filled up, that is very likely what you are looking at, and no recovery brings back data that was never stored.
The list of things not to do is shorter and matters more. Do not format, however reasonably the box asks. Do not shoot a test frame. Do not let free software write its results back onto the card it is reading, which is comfortably the most common way a fully recoverable shoot becomes a partial one. And if the plastic has cracked or the contacts look chewed, stop altogether — one more flex breaks the bonds inside and moves the job into the chip-level bracket, which costs more and takes longer.
A card that refuses a format, reports a fraction of its printed capacity, announces itself as 0 MB, or has become permanently read-only sounds like worse news than it is. All four point at the controller rather than the flash. Controllers do go into a locked read-only state deliberately when their internal wear statistics look bad, and they lose their translation tables outright when power is cut at the wrong moment. Either way the chip in the middle has stopped answering sensibly, and no consumer utility reaches past it. The low-level format tools recommended on forums are a dependable way to finish off a card that still holds something you want.
Getting round a dead controller means going round it rather than arguing with it. Where it still responds at all, the card is imaged behind a write blocker in slow, repeated passes. Where it does not, the flash is read directly from the silicon with a specialist programmer, and then the real work starts: the controller's private scrambling, block interleaving and error correction have to be reconstructed from first principles before anything resembling a file appears. Full-size SD cards often have separate flash and controller packages; most microSD cards are monolithic, meaning the die and the controller are moulded into a single unit and the read has to be taken from test pads on the body itself. That is chip-level work, one of the stated exclusions from no fix, no fee, and it takes 50% of the quoted figure upfront.
Your card is not what gets worked on. The first step is a sector-by-sector image taken through a write blocker, and every decision after that is made against the copy, so a card that is already deteriorating cannot be pushed further by the recovery and no mistake can reach the original. Where enough of the file system survives inside that image, it is repaired and the folder tree comes back looking as the camera left it, filenames and all. Where it does not, the frames are found by their content instead: a JPEG, a CR3, an NEF and an ARW each begin with a recognisable signature, and they can be lifted out of unallocated space without any directory at all.
Two things get checked before anything is described as recovered. Every still is rendered rather than merely listed, because a filename in a results pane and an image that actually draws on screen are separate claims. And video is treated with extra care, since long clips are written across scattered blocks and a partial overwrite tends to damage a file somewhere in the middle rather than remove it cleanly — which is another reason not to shoot anything else on a card that has started misbehaving.
Cards from Berkshire arrive here in a fairly predictable mix: product and conference video shot on the business parks, estate agency and property work around Warfield and Binfield, event and motorsport coverage from the M4 corridor, and students on media and design courses in Reading holding a whole term's field recordings on one card. They live in bags, get swapped with cold hands on wet mornings, pick up damp that never quite leaves, and go through a few thousand insertion cycles that the contacts were never really specified for. The wear is real rather than theoretical.
Packing is simple. Tape the card between two pieces of folded stiff card so it cannot flex, slide that into a padded envelope, and send it tracked to Guildford Data Recovery, Building 2, Ground Floor, Guildford Business Park, Guildford, GU2 8XH. From Bracknell that is roughly forty minutes by road on the A322 and the A3 if you would rather hand it in at reception, which is open Mon–Fri 9:00am–5:30pm; nothing is collected anywhere on this network. Postage for a card costs pennies, the diagnostic costs nothing and closes 2 working days after booking in, and the recovery figure is £250 + VAT for memory cards, USB sticks and pen drives.
The most useful thing you can do with a failing card is nothing at all. A format prompt is a damaged directory, and every frame is sitting behind it exactly where the camera wrote it. It stays that way until something new is written. Eject the card, leave it alone, and let a working copy take all the risk.
Free diagnostic closing 2 working days after your device is booked in, one fixed written quote, and no fix, no fee on logical faults. Cards and USB sticks £250 + VAT, any single drive or SSD £300 + VAT.