Professional service is often required for issues like inaccurate refraction results (requiring calibration), failed keratometry, or non-functional displays and buttons.
| Error Code | Meaning (Standard) | Meaning (Exclusive Manual) | Fix | | :--- | :--- | :--- | :--- | | EE-4 | Printer error | Thermal head resistance out of spec (170–190 ohms) | Replace print head or adjust resistor R12 on power board. | | EE-7 | Communication error | Serial buffer overflow due to baud mismatch | Check opto-isolator IC5 on I/O board. | | EE-23 | Alignment error | CCD line scan defective row 512 | Run pixel mask routine in Service Mode; replace sensor if >10 dead pixels. | topcon kr8900 service manual exclusive