Coldcard MK4 microSD failure – works at first, then later stops reading cards

[Unsaint32]

I’m trying to see if anyone else has experienced this, or if this is a known edge case.

I’ve now had two Coldcard MK4 units show the same microSD failure pattern.

What happens:
MK4 works normally at first.

PSBT signing via microSD works for several transactions.

Then, suddenly, the MK4 can’t find PSBT files on the card.

After that, the problem gets worse:

The MK4 fails the microSD self-test

It can’t format cards

Even microSD cards that previously worked stop working on that device

This happened on my original MK4 and again on a replacement MK4.

Cards tested:
Multiple brand-new and known-good microSD cards

8 GB and 32 GB

FAT32, MBR

Nothing exotic

Linux workflow (in case it matters):
Linux laptop with built-in SD card slot

microSD → SD adapter → laptop

Save PSBT file to the microSD drive

Right-click → Unmount

Wait for popup: “Filesystem has been disconnected”

Remove SD adapter, take out microSD

Insert microSD into MK4

No unsafe removal, no write caching left active.

Why this seems odd:

Cards work initially, then stop

Failure is progressive

Same behavior across two MK4 units

Once triggered, there’s no obvious recovery path

This doesn’t feel like a simple “picky card” issue, because the cards do work at first.

[tenant48]

Have you tried formatting the faulty SD card to FAT 32 on your computer and then writing something to it?
Did you use regular SD cards or Industrial class cards?

Modern conventional flash drives and SD cards (except Industrial class cards) can withstand about 10 rewrite cycles for the following reasons:
• QLC/TLC of the cheapest bin
• Overprovisioning occurs (sometimes 0%)
• Primitive controller
• No DRAM cache
• No temperature control
• Often no proper wear leveling

[Yamane_Keto]

Did you use Sparrow to create PSBT files? I've read many similar cases, and they all involved Sparrow.

Have you tried formatting the faulty SD card to FAT 32 on your computer and then writing something to it?

There's a similar post on Reddit where the user replied that they reformatted their SD card to FAT32, but nothing changed.

[Unsaint32]

Have you tried formatting the faulty SD card to FAT 32 on your computer and then writing something to it?
Did you use regular SD cards or Industrial class cards?

Yes, the cards are fully functional in my Windows and Linux PCs. When I use them with MK4, MK4 cannot read the psbt file in it, cannot format it, cannot pass the sd card part of the device self test. They are all usual micro sd cards. HC.  One of them is Sandisk "Industrial" written on it. Don't make a difference.

[satscraper]

Why this seems odd:

Cards work initially, then stop

Failure is progressive

Same behavior across two MK4 units

Once triggered, there’s no obvious recovery path

This doesn’t feel like a simple “picky card” issue, because the cards do work at first.

But what would happen if you tried the completely new card?

Would it behave the same way?

If not, and it fails immediately, I would try cleaning the contacts in the SD slot ^{maybe blow some compressed air into it or clean it with alcohol}.

Disclaimer. Do this at your own risk.

[tenant48]

Yes, the cards are fully functional in my Windows and Linux PCs. When I use them with MK4, MK4 cannot read the psbt file in it, cannot format it, cannot pass the sd card part of the device self test. They are all usual micro sd cards. HC.  One of them is Sandisk "Industrial" written on it. Don't make a difference.

Then there are most likely two options:
Problems with SD reader contacts or mechanical wear.
Firmware errors that appear after certain sequences of operations.

I'm more inclined to the second option, since new SD cards seem to work somewhat initially. It's worth waiting for the new firmware to be released and testing with it.

[Unsaint32]

According to ChatGPT, the procedure I follow (below) adds invisible data to the sd card, and that might be breaking the MK4.

Right-click → Unmount
Wait for popup: “Filesystem has been disconnected”


When I format the card again in a Windows PC, now it works with MK4.

My Sparrow wallet is in a Linux PC so I have to use a specific code to eject the card in the terminal (not the file manager). Using the file manager did work for a while before so we shall see. I will update.

[dkbit98]

According to ChatGPT, the procedure I follow (below) adds invisible data to the sd card, and that might be breaking the MK4.

Either ChatGPT is stupid or c0ldcard device is stupid  
This is not the first time I heard people complaining about their c0dlcard device getting bricked.
I know that I would never spend my money on this hardware wallet knowing the ego-lunatic liar in charge of that project.

[satscraper]

According to ChatGPT, the procedure I follow (below) adds invisible data to the sd card, and that might be breaking the MK4.

Either ChatGPT is stupid or c0ldcard device is stupid  
This is not the first time I heard people complaining about their c0dlcard device getting bricked.
I know that I would never spend my money on this hardware wallet knowing the ego-lunatic liar in charge of that project.

Modern microSD cards seem to be a jinx for hardware wallets. I remember Lucius complaining about the brand new microSD card that refused to work with Passport Core. They solved the problem by inserting theold, pretty aged microSD card instead. The OP should probably try the same approach and take an older microSD card and insert it into Coldcard MK’s slot. In the past, manufacturers didn’t seem to be greedy using gold to gild the card’s contacts and made the relevant layers thick enough.

[Lucius]

Modern microSD cards seem to be a jinx for hardware wallets. I remember Lucius complaining about the brand new microSD card that refused to work with Passport Core. They solved the problem by inserting theold, pretty aged microSD card instead. The OP should probably try the same approach and take an older microSD card and insert it into Coldcard MK’s slot. In the past, manufacturers didn’t seem to be greedy using gold to gild the card’s contacts and made the relevant layers thick enough.

That's right, the SD card that came with the Passport worked for the first firmware update I did, but on the second attempt the device simply didn't detect it. Since I haven't used SD cards in a very long time, I found an old one from 2008 that did the job without a hitch.

I completely agree that they used to make much better quality stuff, today the goal is just to sell as many as possible and if you want quality you have to pay a premium price for it.

[DaveF]

Modern microSD cards seem to be a jinx for hardware wallets. I remember Lucius complaining about the brand new microSD card that refused to work with Passport Core. They solved the problem by inserting theold, pretty aged microSD card instead. The OP should probably try the same approach and take an older microSD card and insert it into Coldcard MK’s slot. In the past, manufacturers didn’t seem to be greedy using gold to gild the card’s contacts and made the relevant layers thick enough.

I'll make it shorter.
Modern SD cards suck.
I have a bag of them from dash cams, helmet cams, HW wallets, cameras that have all stopped working reliably.
I don't know what changed, but since 2020 (covid era) they are all just crap.

-Dave

[dkbit98]

I'll make it shorter.
Modern SD cards suck.

Not all of them suck.
If you want to have good SD card than buy industrial grade SD cards that have much longer life and they are more reliable.
There is a big difference compared to standard consumer grade cards, and same goes for usb and ssd drives.
Kingston Industrial is probably one of the best, but there are other options available.

[DaveF]

I'll make it shorter.
Modern SD cards suck.

Not all of them suck.
If you want to have good SD card than buy industrial grade SD cards that have much longer life and they are more reliable.
There is a big difference compared to standard consumer grade cards, and same goes for usb and ssd drives.
Kingston Industrial is probably one of the best, but there are other options available.

Nope, I have a few bad industrial SD cards too. Yeah, they had a hard life but when the ones from 2018 are still kicking and the ones from 2023 are not I just put them all in the "they are all crap" bucket.

Both Kingston and Swissbit.

It's to the point that they are so cheap it's not worth caring just put them in the bag for destroying later in case there is any data on them and put in a new one.

-Dave

[tenant48]

Nope, I have a few bad industrial SD cards too. Yeah, they had a hard life but when the ones from 2018 are still kicking and the ones from 2023 are not I just put them all in the "they are all crap" bucket.

Both Kingston and Swissbit.

It's to the point that they are so cheap it's not worth caring just put them in the bag for destroying later in case there is any data on them and put in a new one.

If you have a large number of flash drives and SD cards, you can try recovering them using low-level format utilities. I've been able to restore flash drives and SD cards to working order in some cases. Naturally, all data on them will be deleted after this procedure. Recovery is only possible in the event of a software failure, not physical damage to the memory cells.

[Unsaint32]

It turns out the culprit was a power issue. My USB-C power adapter that plugs into a wall socket was the issue. I used a different newer adapter, and now it works great. The "bad" adapter still works well for other stuff such as charging phone, etc. I guess Coldcard is sensitive to power quality.

[rdluffy]

It turns out the culprit was a power issue. My USB-C power adapter that plugs into a wall socket was the issue. I used a different newer adapter, and now it works great. The "bad" adapter still works well for other stuff such as charging phone, etc. I guess Coldcard is sensitive to power quality.

I'm glad you managed to solve the problem
I'm not surprised that the problem was the cable, even though it wasn't the first thing that came to mind

I have some cables, both USB-C and micro USB, that work strangely on certain devices
You think everything is OK because you've connected it, but there isn't enough power, usually due to the poor quality of the cable, and the device behaves strangely

The lesson here is to always have a spare cable and try to buy a good quality one
I really like Ugreen USB-C cables, they're good and reasonably priced too