Test, diagnose and fix ESC/POS thermal receipt printers over your local network — straight from your iPhone. No drivers, no laptop, no guesswork.
Need help? Email marcus@lhkmarcus.com and we'll get back to you. Please include your printer make/model, your device model and iOS version.
The scan doesn't find my printer
Make sure your iPhone and the printer are on the same WiFi network and subnet — a phone on guest WiFi usually can't see the wired LAN. The printer needs a network interface (an Ethernet/LAN port or built-in WiFi); a USB-only or Bluetooth-only printer won't appear. Check that port 9100 (RAW/JetDirect printing) is enabled on the printer — it is on almost every ESC/POS model. If the scan still misses it, print the printer's self-test page to find its IP address and add it manually in the app.
Chinese characters or accents come out garbled on receipts
That's a codepage mismatch: your POS software is sending text in one encoding while the printer's firmware is decoding it as another. Open PrintDoctor's Codepage Matrix page — it prints your text through every codepage the firmware supports so you can see, on paper, which one renders correctly. Then set that same codepage in your POS software (and/or the printer's default) and the garbling disappears.
The cash drawer doesn't open
First check the physical link: the drawer connects to the printer's DK port (the RJ11/phone-style jack) with an RJ11 cable — not to the network. If it's plugged in and still won't fire, the drawer may be wired to the other kick pin: in the app, try pin 2 vs pin 5 on the cash-drawer test — different drawers and printers pair differently, and one of the two almost always works.
Why is there no Bluetooth support?
Most Bluetooth receipt printers use classic Bluetooth SPP, which iPhones cannot talk to — Apple doesn't expose that profile to apps. That's an iOS platform limit, not an app setting. Network (LAN/WiFi) printers work today, and BLE printer support is on the roadmap for models that offer it.
Can I try the app without a printer?
Yes — use the built-in Virtual Demo Printer. It behaves like a real networked ESC/POS printer, so you can try every feature — test prints, codepage tests, logo printing, drawer kicks — with no hardware at all.
Does the app send my data anywhere?
No. The only network traffic is the direct connection between your phone and printers on your own local network; nothing is uploaded and there are no accounts or analytics (see our Privacy Policy).