Failure
After restarting the computer, services, or USB printer, printouts contain incorrect characters, codes, numbers, or unexpected content, even though no changes were made to the print queue or the document being sent.
Cause
Residual spool content is being sent to the printer.
This behavior is associated with SPL files generated by the Windows spooler. Without collecting these files, it is not possible to identify which content is being sent to the queue, causing the incorrect print output.
Related technical context:
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The problem may occur in environments with both a USB printer and a thermal printer connected to the same computer.
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Analysis depends on the SPL files.
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Restarting the spooler may delete the files needed for investigation.
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The default path for these files is: C:\Windows\System32\spool\Printers.
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The problem may be related to the content sent by the spooler, environment policy, print queue rule, or interaction with printing services.
Solution
Warning
Once you identify the problem, do not immediately restart the spooler. Restarting the spooler may temporarily normalize the environment but removes necessary evidence.
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Pause the affected print queue
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Send a test print job to generate the SPL file
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Access the path C:\Windows\System32\spool\Printers
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Copy the generated SPL files
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Store the files in a secure location for analysis
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Release the queue only after collecting the necessary files
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Forward the SPL files for technical analysis
If the environment is in production and needs to be released, restart the spooler only after collecting the files.
If necessary, temporarily disable advanced printing services until the analysis is complete.
After applying the recommended fix or update, run another test print and monitor whether the incorrect characters reappear.
Additional information:
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Without the SPL files, technical analysis is limited.
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The behavior may depend on environment policies, print queue rules, GPOs, or integration with printing components.
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Collect the files before performing corrective actions that clear the spooler.
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The problem should not be processed solely as a printer failure without analyzing the content sent to the spool.
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In mission-critical environments, establish a rapid collection procedure before restarting the spooler.