Navman VHF 7100 Radio neither receiving nor transmitting

Verify the offset is correct. Was it programmed with chirp or another software. Transmit may have been disabled or programmed out of band.

Have you checked your settings on your receiver to see if they match the repeater you can't receive? CTCSS, DCS, and the digital radio settings can all affect this.

It is possible your Code for transmit is different than your Code for receive. Cobra makes so many models, you are not giving enough information. Also, Transmit takes a LOT of power, so even if everything is setup, if your batts are weak or old, the radio will receive, but not transmit. Also check your antenna, make sure it is tight and NEVER transmit without an antenna. Yes, all lights will work even with old batteries.

Most problems with radios that receive but do not transmit are antenna or antenna wire/connector issues. It's easy to receive with a marginal antenna but transmitting requires a good working antenna. If you have a SWR meter or can get your hands on one, install it in line with the antenna and test for reflected power. Of course, make sure your TX light comes on when you depress the mic switch. If not, switch mic and try again.
Hope this is helpful! Reply if u can.

You may have a bad microphone, not uncommon problem.

Too late to help op, but trying to fix one with same symptoms, found a broken wire in the microphone cable near the handset, as I'd suspected. The cable appears to be a curly shielded 8 conductor, one of which (presumably the mike) appears to also have a shield - found a seller on ebay US that appears a suitable cable for about £16

Yes if the tip is broken, the antenna will receive, but not transmit properly. The make an antenna that has a 32" stainless steel antenna with a small metal "can". Can mount it anywhere.

The main cause for lack of reception or transmit distance is the PL259 connector on the antenna coax that plugs into the back of the VHF. Check to make sure this connector is a high quality, marine grade connector. If it screws on and the coax shield is not soldered to the connector I recommend replacing the connector and soldering it. If the problem still exists I would try a different antenna to see if this is the problem. It is possible that the radio itself has a problem, but check these other issues first. Raymarine has a 3 year warranty on their VHFs so you could send it back for a no charge repair if the antenna doesn't solve your problem.

Good luck!

You may have a bad antenna. What happens is a lot of guys carry their radios around by the antenna, inside the connection to the antenna is weak and can crack at the solder joint, thus opening up the antenna circuit and prevent you from transmitting any power out. Our Motorola hand helds have this problem, they are weak at the antenna connector and guys swing them around by the antenna end up breaking them.
Your next problem is that if the radios have been used often enough with a faulty antenna circuit, your final amplifiers are probably toast from transmitting into an open antenna circuit, causing all the power to be reflected back into the radio and burning out the final amplifiers

Check your microphone by swapping with another duplicate. If no differance, you will need a SWR meter (standing wave ratio) to find the culprit. It attaches in line of the coax and determinds power out and reflected power. The reading should be 25 watts foward and max of 1 reflected.