Question edited for clarity.
Make sure you got the correct transducer Your model comes in single frequency and dual frequency. Make sure the connection on the back of the unit is good and you have no corroded or missing pins. Make sure the software is up to date.
Lowrance LMS-525C DF Fish Finder Parts
Product Description: Designed for salt water or downrigger tracking, this dual-frequency sonar/GPS chartplotter
provides additional 50 kHz readings, in addition to a high-res 480 x 480 display on a 5" screen
and many professional features.
* Dual-frequency 50/200 kHz
* Precision 12-parallel channel external GPS+WAAS receiver
* Lowrance radar compatible
* LowranceNET® networking (NMEA 2000® certification pending)
* High-speed ethernet connection links multiple Lowrance display units and modules to
operate independently on shared network data, including sonar
200 khz transducer PDRT-WBL Part #106-89
Shoot-thru-hull mount, 20 degree pod type with remote temperature (200 kHz). (20 ft cable)
Dual Frequency Transducer HP-DFBL260 Part #106-82
Thru-hull-mount, dual frequency bronze housing, high-power multiple element (50 kHz 19 degree
& 200 kHz 6 degree).
HST-DFSBL Part #106-77
Transom-mount, dual frequency skimmer with built-in temperature sensor. (25 feet of cable)
https://www.google.com/search?q=lowrance+lms-525c+df+software+update
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