LIMS Printer Troubleshooting Guide

Category: LIMS Troubleshooting Tags: LIMS, Printer, QZ Tray, Windows, Troubleshooting, Hardware

Issue 1: Printer Only Works When Specific User Logged In

Check Device Manager

1. Press Windows + R
2. Type devmgmt.msc and press Enter
3. Expand "Printers" or "Print queues"
4. Right-click your problem printer → "Properties"
5. Click "Driver" tab
6. Look at driver file path - if it contains a username folder, it's user-specific

Check Printer Properties & Permissions

1. Press Windows + R
2. Type control printers and press Enter
3. Right-click your problem printer → "Properties"
4. Click "Security" tab
5. Check if "Everyone" has "Print" permissions
6. If not: Click "Add" → type "Everyone" → "Check Names" → OK → check "Print" box

Check Print Spooler Service

1. Press Windows + R
2. Type services.msc and press Enter
3. Find "Print Spooler" → Right-click → "Properties"
4. "Log On" tab → make sure "Local System account" is selected
5. Click "Apply" if you changed anything

Check Registry (Advanced)

1. Press Windows + R
2. Type regedit and press Enter
3. Navigate to: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Print\Printers
4. Look for your printer - if it's here, it's system-wide
5. Also check: HKEY_CURRENT_USER\Printers - if only here, it's user-specific

Check Printer Sharing

1. Press Windows + R
2. Type control printers and press Enter
3. Right-click problem printer → "Properties"
4. Click "Sharing" tab
5. Check "Share this printer" box
6. Give it a simple share name (no spaces or special characters)

Check LIMS Service Account Permissions

1. Press Windows + R
2. Type services.msc and press Enter
3. Find your LIMS service → Right-click → "Properties"
4. Note the account it runs under ("Log On" tab)
5. Go back to printer properties → "Security" tab
6. Add that service account with "Print" permissions

Issue 2: QZ Tray Intermittent Printing (Random Success/Failure)

Check QZ Tray Status

1. Look for QZ Tray icon in system tray (bottom-right corner)
2. If not visible, click small up arrow to show hidden icons
3. Right-click QZ Tray icon → "About" to check if running properly
4. Note version number
5. If not running: Start Menu → find QZ Tray → launch it

Restart QZ Tray Service

1. Right-click QZ Tray icon → "Exit" or "Quit"
2. Press Windows + R
3. Type services.msc and press Enter
4. Look for "QZ Tray" service (if installed as service)
5. Right-click → "Restart"
6. If no service, manually restart from Start Menu

Check Windows Firewall

1. Press Windows + R
2. Type firewall.cpl and press Enter
3. Click "Allow a program or feature through Windows Defender Firewall"
4. Find QZ Tray in the list, make sure both "Private" and "Public" boxes are checked
5. If not listed: Click "Allow another app" → "Browse" → navigate to QZ Tray installation folder
6. Also check for "Java" entries and ensure they're allowed

Clear Print Queue

1. Press Windows + R
2. Type control printers and press Enter
3. Double-click your label printer to open queue
4. If jobs are stuck: Click "Printer" menu → "Cancel All Documents"
5. Close queue window

Test QZ Tray Connection

1. Open any web browser
2. Type in address bar: localhost:8181 (or try localhost:8182)
3. Should show QZ Tray demo page
4. Click "Print Test" button to test printer response
5. If page doesn't load, QZ Tray isn't communicating properly

Check QZ Tray Logs

1. Press Windows + R
2. Type %appdata% and press Enter
3. Look for "qz" folder → open it → open "logs" folder
4. Open the most recent log file with Notepad
5. Look for errors related to certificates, WebSocket connections, or printer communication

Check Certificates (Common QZ Issue)

1. Open QZ Tray demo page: localhost:8181
2. Look for certificate warnings in browser
3. If certificate errors: Close QZ Tray completely
4. Delete certificate files (usually in QZ Tray installation folder)
5. Restart QZ Tray - it will regenerate certificates

Advanced Print Queue Reset

1. Press Windows + R
2. Type services.msc and press Enter
3. Find "Print Spooler" → Right-click → "Stop"
4. Press Windows + R
5. Type %windir%\System32\spool\PRINTERS and press Enter
6. Delete all files in this folder
7. Go back to Services → Right-click "Print Spooler" → "Start"

Check Network Printer Connection (if applicable)

1. Press Windows + R
2. Type cmd and press Enter
3. Type: ping [printer-ip-address] and press Enter
4. Should get replies - if timeouts, network issue
5. Also try: telnet [printer-ip-address] 9100 (common printer port)

LIMS-Specific Checks

1. Open LIMS software
2. Go to printer/label settings (location varies by LIMS)
3. Verify correct printer is selected as default
4. Check if there's a "Test Print" option in LIMS
5. Try printing directly from LIMS vs through browser
6. Check LIMS logs for print job errors

Browser-Specific Troubleshooting

1. Try different browsers (Chrome, Firefox, Edge)
2. Clear browser cache and cookies for LIMS site
3. Disable browser extensions temporarily
4. Check if browser is blocking WebSocket connections
5. Add LIMS site to trusted sites if using Internet Explorer/Edge

Port and Communication Check

1. Press Windows + R
2. Type cmd and press Enter
3. Type: netstat -an | find "8181" and press Enter
4. Should show QZ Tray listening on port 8181
5. If not, QZ Tray isn't running properly or port is blocked

Reinstall QZ Tray (Last Resort)

1. Download latest QZ Tray from official site
2. Close QZ Tray completely
3. Uninstall current version from Control Panel
4. Delete remaining QZ Tray folders
5. Install new version as Administrator
6. Reconfigure printer settings in LIMS

Additional Edge Cases & Advanced Troubleshooting

Multiple QZ Tray Instances Running

1. Press Ctrl + Shift + Esc to open Task Manager
2. Click "Details" tab
3. Look for multiple "java.exe" processes or "qz-tray.exe"
4. End all QZ Tray related processes
5. Restart QZ Tray once

Java Version Conflicts (QZ Tray uses Java)

1. Press Windows + R
2. Type cmd and press Enter
3. Type java -version and press Enter
4. Note Java version (QZ Tray requires specific Java versions)
5. If wrong version, update Java or reinstall QZ Tray with bundled Java

Windows Updates Breaking Printer Drivers

1. Press Windows + R
2. Type appwiz.cpl and press Enter
3. Click "View installed updates"
4. Look for recent Windows updates around the time printing stopped working
5. Try uninstalling recent printer-related updates
6. Reinstall printer drivers after

Antivirus Blocking QZ Tray

1. Open your antivirus software
2. Look for "Quarantine" or "Blocked items"
3. Check if QZ Tray files were quarantined
4. Add QZ Tray installation folder to antivirus exclusions
5. Restore quarantined files and restart QZ Tray

Group Policy Restrictions

1. Press Windows + R
2. Type gpedit.msc and press Enter (if available)
3. Navigate to: Computer Configuration → Administrative Templates → Printers
4. Check for policies restricting printer installation or usage
5. Also check: User Configuration → Administrative Templates → Control Panel → Printers

USB vs Network Printer Port Switching

1. Press Windows + R
2. Type control printers and press Enter
3. Right-click printer → "Properties"
4. Click "Ports" tab
5. Note if port changed (USB001 vs IP address vs LPT)
6. Select correct port or add new port if needed

Printer Going to Sleep/Offline Mode

1. Press Windows + R
2. Type control printers and press Enter
3. Right-click printer → "Properties"
4. Click "Advanced" tab
5. Uncheck "Enable bidirectional support" if checked
6. Check printer's network settings for sleep/power saving modes

IP Address Changes (Network Printers)

1. Press Windows + R
2. Type control printers and press Enter
3. Right-click network printer → "Properties"
4. Click "Ports" tab → "Configure Port"
5. Verify IP address matches printer's actual IP
6. Print network config page from printer to confirm IP

Browser Popup Blockers Interfering

1. Open browser settings
2. Find "Pop-ups and redirects" or "Notifications"
3. Add LIMS website to allowed sites
4. Also check browser extensions that might block content
5. Try browser in incognito/private mode to test

Certificate Expiration Issues

1. Open QZ Tray demo: localhost:8181
2. Check browser developer tools (F12) for certificate errors
3. Look at certificate expiration date
4. Press Windows + R
5. Type %appdata%\qz and press Enter
6. Delete "auth" folder to regenerate certificates

Multiple Users Printing Simultaneously

1. Press Windows + R
2. Type control printers and press Enter
3. Right-click printer → "Properties"
4. Click "Advanced" tab
5. Set "Priority" to higher number for important users
6. Enable "Print spooled documents first" option

Terminal Services/Remote Desktop Issues

1. Check if printing works locally vs through RDP
2. Press Windows + R
3. Type gpedit.msc and press Enter
4. Navigate to: Computer Configuration → Administrative Templates → Windows Components → Remote Desktop Services
5. Check printer redirection policies
6. May need to install printer drivers on RDP server

Label Stock/Size Mismatch

1. Press Windows + R
2. Type control printers and press Enter
3. Right-click label printer → "Printing Preferences"
4. Check paper size settings match actual label stock
5. Verify print density/darkness settings
6. Check if printer needs calibration

Time Synchronization Issues

1. Press Windows + R
2. Type timedate.cpl and press Enter
3. Click "Internet Time" tab → "Change settings"
4. Ensure time sync is enabled and working
5. LIMS and QZ Tray may fail if system time is wrong

LIMS Database Connection Issues

1. Check LIMS logs for database connection errors
2. Printing may fail if LIMS can't access printer configuration data
3. Test LIMS connectivity to database server
4. Check if print job records are being created in LIMS database

Thermal Printer Head Issues (Hardware)

1. Print self-test page directly from printer (usually hold feed button)
2. Check for faded areas, streaks, or missing lines
3. Clean printer head with alcohol and cotton swab
4. Replace printer head if cleaning doesn't help

Multiple LIMS Instances Conflicting

1. Check Task Manager for multiple LIMS processes
2. Check different browser tabs/windows with LIMS open
3. Only one LIMS session should control QZ Tray at a time
4. Log out of other LIMS sessions

Print Server Issues (Enterprise Environments)

1. Press Windows + R
2. Type \\printserver-name and press Enter (replace with actual server)
3. Check if print server is accessible
4. Try adding printer directly by IP instead of through print server
5. Check print server event logs for errors

HTTPS/SSL Issues with Localhost

1. Some browsers block mixed content (HTTP localhost from HTTPS LIMS)
2. Try accessing LIMS through HTTP instead of HTTPS for testing
3. Or configure QZ Tray for HTTPS (more complex setup)
4. Check browser console (F12) for mixed content warnings

Driver Version Conflicts

1. Press Windows + R
2. Type printmanagement.msc and press Enter
3. Expand "Drivers" to see all installed printer drivers
4. Look for multiple versions of same driver
5. Remove old/duplicate driver versions
6. Keep only the latest working version

Session Timeout Issues

1. LIMS user sessions may timeout, breaking QZ Tray connection
2. Check LIMS session timeout settings
3. QZ Tray may need to be restarted after LIMS re-login
4. Some LIMS require re-selecting printer after session renewal