This is actually a good question. I'm not sure there is a way to test it off water. Maybe it's just me but I have never heard of a black box going bad. Most problems with the transducer is due to nick wires. I would check the transducer cord for any cracks or nicks. I looked for a used unit for months with no success. I purchased a new unit from Bass Pro shop because they had a special. This was before the lvs34 came up and the market became flooded with the LVS32 units. I did buy a used 93SV from a forum member and it works great.