The five-minute separation
| What you see | What it means | Severity |
|---|---|---|
| No LEDs, nothing at all | Supply problem — measure 24 VDC at the panel's own terminals; check the fuse and the supply under load, not just its idle LED | Often a $40 fix |
| Power LED on, screen black — flashlight shows a faint image | Backlight failure. Aim a flashlight at an angle: a ghost of the screen means the display and computer are fine | Repairable; routine on CCFL-era panels |
| Power LED on, truly no image under flashlight | Display assembly or its board | Repairable, costs more |
| Shows boot logo, then black | Firmware or application failure — the display just proved it works. Look for maintenance/safe-mode boot options for your model | Software-side; often recoverable |
| Screen black, but touch beeps or the PLC reacts to presses | Runtime alive, display-side fault only — blind operation is a burn risk; stop guessing at invisible buttons | Repairable |
Full step-by-step triage, including what to check in the cabinet before blaming the panel: the 10-minute line-down guide.
Brand notes
- Allen-Bradley PanelView: symptoms decoded model by model in the PanelView Plus 7 guide; touch-specific faults in the touchscreen guide. Older PanelView families may not be worth the repair — check the obsolescence timeline first.
- Siemens KTP / Comfort Panel: the same flashlight logic applies; symptom walkthrough in the Siemens guide, and if the unit is from a retired TP/OP generation, the replacement options guide covers the paths.
- Mitsubishi GOT: touch the screen before anything — the GOT's screensaver blanks the backlight on a timer and fools everyone: the GOT guide.
- Weintek, Delta, Pro-face, Red Lion, Magelis: the electrical triage is identical — supply, backlight, display, boot. Brand changes the recovery doors and where the project files live: Weintek · Delta · Pro-face · Red Lion · Magelis.
Repair, replace or bridge
- Repair: backlights, supplies and display assemblies are routinely rebuilt for $300–$1,000, typically 1–2 weeks with shipping. The right call for a healthy panel with one dead subsystem.
- Replace: the honest math depends on whether your model is current or retired — a discontinued unit pushes you into scarcity-priced spares or a migration decision. That's a strategy question, not a shopping question.
- Bridge first: either way, the operator needs a screen today. That's the 15-minute job below — and it takes the panic out of the repair-or-replace decision.
Keep producing while you wait
Have the panel project export? Drop a FactoryTalk View, TIA Portal, Weintek or CSV export into our free HMI project converter — it runs in your browser, the file never leaves your PC, and every display becomes a page of buttons, indicators and values for the app, with the real tag names already in place.
Today, from a phone: the free LineKeeper app for iPhone and iPad speaks EtherNet/IP, Siemens S7 and Modbus TCP. On Allen-Bradley Logix it reads the controller's own tag list automatically; on S7 and Modbus you add the addresses you care about. Build a dashboard and an operator panel with start/stop buttons in about 15 minutes, mount a spare iPad in full-screen panel mode, and the operator has a screen before the first repair quote arrives. Reading is free; writes are a one-time unlock with confirmation and limit checks on every value.
The 15-minute temporary panel
Zero-config tag browser for Logix, drag-and-drop dashboard, operator panel, alarms — no changes to the PLC program.
On a desktop? Scan with your iPhone or iPad to get the free app.For the machine itself: the LineKeeper device — in development — is a self-contained 7″ or 10″ touchscreen built to live on the machine permanently — the same drag-and-drop screens, plus what a phone shouldn't carry:
- Live view of every tag, refreshed twice a second — plus write access with a full audit log
- Operator panel: start/stop, indicators, setpoints — hold-to-run buttons release safely
- Stays useful after the repair: data logging, dashboards, machine diagnostics
Small hardware that helps while the panel is out
- GL.iNet Opal travel router — Wi-Fi into the machine network from a spare switch port, so the phone app can stand in as the screen today.
- Anker USB-C to gigabit Ethernet adapter — wired straight into a spare switch port, the phone sees the controller in seconds; USB-C iPhones and iPads need no drivers.
- VIVO pole-mount VESA arm — puts the temporary screen at eye level on a machine post instead of a chair.
- TICONN IP67 enclosure with clear cover — houses the gateway or Wi-Fi bridge on the machine without bare boards on the rail.
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