Troubleshooting Speed and Temperature on Raymarine Instruments – Step-by-Step Guide

Common causes of incorrect speed and temperature on Raymarine instruments – How to test transducers and thermistors

If the speed or temperature on your Raymarine instrument display (e.g., ST40, i40, ST60, ST60+, ST70, i50, i70, ITC-5) is not working correctly, it is usually due to two common causes. This guide will help you identify the problem and fix it.

Step 1: Check the speed instrument

Look at your speed display. For speed, does it show dashes (-.- knots) or does it show zeros (0.0 knots)?

• Shows zeros: The problem is likely the speed sensor. See our FAQ to check if the speed circuit is working: Test speed transducer through water.
• Shows dashes: This indicates that the thermistor in the transducer is broken, which also causes the water temperature to be incorrect (or show dashes). The instruments use the thermistor to determine if a transducer is connected – no thermistor = no speed data.

Step 2: Test the thermistor

The thermistor is measured between the brown and white wires on the speed transducer. Do the following:

1. Disconnect the brown and white wires from the instrument (or ITC-5).
2. Measure the resistance with a multimeter. You can measure in both directions.
3. If you have a manually adjustable multimeter, set it to 20k (20,000 ohms).

Expected resistance values

Below is a table showing approximate resistance values at different temperatures. Example: 11K ohm ≈ 23°C. If the resistance is drastically different (e.g., open circuit), the thermistor is defective.

Solution

To restore the water temperature, you must replace the transducer, as these are completely sealed and cannot be repaired.