How to check a microSD card after changing readers

Your microSD card worked in one reader, but files disappear or a capacity check fails after you switch readers. The reader can affect what the computer sees, so a single failure does not prove the card is fake.

The Fake USB & SD Check fills the card with test data and reads it back to check whether its reported capacity is real. Back up any files you need before testing. The test writes across the card, and a fake-capacity card can overwrite existing data.

Test the card in both readers

1. On a computer, open the Fake USB & SD Check in Chrome or Edge. The tool works in those browsers on a computer. Copy important files off the microSD card before you start.
2. Insert the card into the first reader and connect it to the computer. When the browser asks you to choose a drive or location, select the microSD card, not another removable drive.
3. Run the full capacity check and let it finish. Do not remove the card, disconnect the reader, or let the computer go to sleep during the test.
4. Safely eject the card, then move the same card to the second reader. Run the check again under the same conditions.
5. Compare whether each run completes the write and read-back checks, and note if a failure happens at a similar point. The test checks capacity and data integrity, not transfer speed.

Use the same computer for both runs if you can. That keeps the card, computer, and browser consistent while you compare the readers. For a separate look at why reader choice changes speed measurements, see Why card reader speed affects SD card test results.

What the result means

The card passes in both readers

The card's full tested capacity was readable after the test wrote data to it. The earlier problem may have been a loose connection, an interrupted transfer, or a temporary issue. A pass is useful evidence, but keep a separate backup of important files.

The card passes in one reader but fails in the other

This points more strongly to the failing reader, its adapter, its USB port, or its compatibility with the card. It does not prove the card is genuine, because a reader can fail to communicate reliably even with a good card.

Both readers fail at a similar point

A repeatable failure across two readers makes the card itself a stronger suspect, especially if the test cannot read back data written near the card's reported capacity. A counterfeit card may report more space than it can store, causing newer data to overwrite older data.

The computer reports a smaller card size in one reader

That can indicate an older or incompatible reader, a contact problem, or a card issue. The size shown by the computer is only the capacity being reported, not proof that the entire space can store data safely. Check the reader's supported card type and compare the result in another reader.

The result changes between runs

Inconsistent results can come from a loose connection, a failing reader, a busy computer, or an unstable card. Repeat the test with the computer plugged into power and avoid file transfers or other heavy tasks at the same time.

How to troubleshoot a failure

1. Confirm you selected the microSD card. If several removable drives are connected, check the drive name and reported size before choosing it. Disconnect other USB storage first if you are unsure.
2. Reseat the card and adapter. Remove the card, check that it sits fully in the reader, and insert it again. If you use a microSD-to-SD adapter, try another adapter if available.
3. Change the USB connection. Connect the reader directly to another computer port instead of through a hub. Test the same card again, then try a different reader if the result still fails.
4. Check reader compatibility. Look for the card type and capacity supported by the reader. Some older readers do not support newer SDXC cards or their full capacity, which can cause detection problems.
5. Close anything using the card. Stop file transfers and close File Explorer windows or apps that may be reading the card. Safely eject it before moving it between readers, and never unplug it while the test is running.
6. Do not format it as a capacity fix. Formatting erases files and cannot make a fake card hold its advertised size. If the card passes the full test but still has file-system errors, copy your data elsewhere before considering a format, then test again.

When the card itself is likely faulty

If the same card fails the read-back check in two compatible readers connected to different ports, treat it as unreliable. Do not store photos, videos, or backups on it. If it is new, keep the test details and request a refund or replacement from the seller. If it has been in use for a long time, replace it and recover any readable files before testing again.

A reader change can explain a different detection result, but it cannot increase the card's real storage capacity. Keep another copy of anything you cannot afford to lose.