Zebra QLn420 Disconnects After Single Label Printing

Hoping that someone can help me understand the issue I'm coming across.


I have hundreds of Zebra Printers in the field currently. Many are older than 2 years. I've just deployed three new printers and each printer is having the same problem - they lose connection with my software upon printing multiple labels. I've been wracking my brain trying to troubleshoot the configurations since my application (nor the iOS version has changed) then I noticed two small differences between the configuration of the 3 new printers and my in-house debug unit.


1. My debug unit (which works perfectly) is running Firmware V68.19.7 and utilizes Bluetooth v4.2.1

2. The new printer (which fails every time) is running on Firmware V68.20.01 and utilizes Bluetooth v4.3.1p1


In terms of configuring the printer, I do very minimal through the Zebra Setup Utility. Two small sets of commands.

The first to define my label settings




















And the second to define my bluetooth/connectivity

! U1 setvar "bluetooth.enable" "on"

! U1 setvar "bluetooth.discoverable" "on"

! U1 setvar "bluetooth.minimum_security_mode" "1"

! U1 setvar "bluetooth.bonding" "on"

! U1 setvar "bluetooth.enable_reconnect" "iOS_only"

! U1 do "device.reset" ""


On the NEW Printers I can connect via Bluetooth in the iOS settings, and show as paired on the printer. Then I can open my application and print a test page as well as calibrate the page size (we have two interchangable labels). But then when I go in to the actual data I'm printing (receipts, labels or tags) if I attempt to print more than one item in succession the printer shows as disconnected in my application but still displays as connected in iOS.


Since my application code has not changed - nor has the Apple iOS settings, my only thought is that it has something to do with the Bluetooth supported version on the printer itself. Is there come command that I could run to either roll back the bluetooth driver to 4.2.1 or a command that will stop from a disconnect while printing?


Any thoughts would be greatly appreciated.

Anonymous (not verified)
Hi Mattew,I didn't see

Hi Mattew,

I didn't see anything in the release notes that would cause this.  Unfortunately there is no way to downgrade the Bluetooth driver on the printer without downgrading the firmware entirely.  The old firmware is still available on Zebra.com.

The only command I can think of that might effect this, as we've had issues with iOS in the past, is the Bluetooth scan window.  The older printers (edit: firmware) have a window of 30 (hard coded), I think the new ones default to 60.  The JSON for the command is:


to get the current value,


to set it to 60.

If this doesn't work, I recommend contacting our tech support.

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Matthew Bailey
Thank you for the quick

Thank you for the quick response Robin,

I went ahead and tried rolling back the firmware to the currently available on Zebra (68.18.8z) and now the "bluetooth.enable_reconnect" stores a value of "?" and won't connect to any of my iOS devices.

I couldn't find anything in the release notes after this firmware that stated that this was a change in a later version update. Any ideas why that value would have changed? or any idea how I can find the Firmware version that I currently have installed on my working printers (68.19.7z)?

I opened a case (ID# 03331739) and was given the firmware for 68.19.7, so I flashed it to that version and I am working perfectly, but it still makes no sense as to why it would work on this version but not the new 68.20.01. The only explanation that I can see is the bluetooth driver 4.3 not working properly with iOS.

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