I once asked Shoreline this themselves (I wanted a circuit diagram). They didnt repair them at all, they simply replaced them.
Its possible someone like Mantsbrite Marine at Maldon will have a go, as will some other good electronic repairers, but they'll have to do so without support.
That suprised me - I thought ultimately I would be paying money to Shorline. Do you have their contact details, by the way? My 'Compact RT' seems to have stopped transmitting. Press the PTT and all you can receive (on the handheld) is a crackling hissing noise, so it's trying but not getting anything out. Rx is ok. Antenna is ok (tried another). All channels the same.
It failed rapidly but not instantly - over the course of two days it got worse until it failed to get anything meaningful out. I took the top off expecting to find something I would recognise but as is the way these days just a load of chips.
If you are getting something on the HH then the carrier is switching on, but perhaps not being modulated. That suggests the mike switch is ok, but perhaps a problem with the mike itself. Have you checked the connector on the mike for dry/loose joints? Take it apart and have a waggle of the wires.
If that looks ok, try re-connecting the mike without doing up the lock ring and waggle it about whilst trying again. Possibly just a poor connection somewhere.
Shoreline sourced the unit from an (unnamed) far eastern manufacturer, and never held spares or info. They usually considered repair uneconomic and just replaced the box. Unfortunately Shoreline went bust a few years ago, so no help there.
If you want it fixed and its not just loose wires (often is, but unlikely from your description) it needs specialist test gear which means a decent repairer, who may not be able to get the spares anyway.
I've got most of the gear, and if you really are stuck, PM me and I'll see what I can do, but no promises. Others here may be more qualified and have more time.
Eyup. I'm probably a bit late but I have one of them in bits in front of me right now. When you switch it on it goes straight into Tx and hisses at you. What had happened was that the Mic/plug socket had come loose, just enough to twist, rotate, causing a short between the tiny pcb which attaches to the back of the Mic socket and a pin on the volume pot inside.
This picture shows, the unit upside down with the cover removed. Looking from where the red/black power leads exit the body towards the front. This is the corner of the unit where the Mic socket is and the volume pot.
Volume and sqwelch, love that word, pots at the bottom and a small oblong of circuit above which is connected to the Mic socket behind it. You can see the 4 pins on the left side. The above picture is how it should look, the next how not.
Here the socket has come just loose enough to rotate causing it to short out on the legs of the volume pot.
It is possible to rotate it back, lift it up, and then re-tighten the 'nut' slotted ring that tightens it on the front. I drove it round with a fine bladed flat screwdriver and a sharp thwack.
I caution you about taking the facia off, the 4 screws that hold the black plastic tags on rip up the chassis going back in and, there is a tiny capacitor (arrow) soldered spread-eagled to the shell of the sqwelsh pot and the main circuit and it would be very easy to tear it apart.
Now I have to work out which pin does what so I can wire a new Mic for it to test........