Marine Electronics Questions? Ask a Technician for Answers ASAP
If the wiring and connections are all ok and free from corrosion or damage, then the transducer has likely failed and will need to be replaced.
You can confirm this by swapping in another working transducer.
These transducers are tied together one should be working I would think. If the 10 is the only one on it doesn't work. If the 8 is the only one on it doesn't work. I find it hard to believe they both would fail at the same time.
In that case the fault is more likely to be in the wiring or connections if you are certain the transducer is working.