Has your IC746 stopped transmitting but works fine on receive? Or is the power output low? The IC746 pulls about 20A on transmit and it is essential that all the connections in the DC supply are clean and very low resistance. Otherwise the supply volts to the PA get pulled right down and the rig won't transmit.
This can look very much like a PA fault! To check it you need to unscrew the top cover and measure the volts where the 13.8V DC connects to the PCB. Connect the rig to a dummy load, switch to FM and make sure the power control is turned right up. If the volts measured at the PCB inside the rig drop significantly when the rig is switched to transmit then you almost certainly have a problem with the supply lead. There are two usual culprits:
1. The fuse holders in the DC lead may need cleaning or replacing and are frequently the cause of these symptoms. After repeated problems with my fuse holders I replaced them with audio quality automotive fuses.
2. The Molex power connector on my IC746 was getting hot and the rig would sometimes cut out on transmit. So I replaced it with 30A Powerpoles.
There is no need to drill holes in the rig.
Unscrew the top covers and remove the Molex connector. It just unclips from the back panel. Carefully remove or clip off the IC746 internal power leads from the Molex. With care they are just long enough to be reused
To mount the Powerpoles.
File about 1mm off a pair of Powepole mounting plates so they sit nicely in the recess on the back panel of the IC-746 where the Molex was.
Make up two small aluminium plates which will clamp the Powerpole mounting plate in place inside the IC746. Alternatively you can use a second set of Powerpole mounting brackets the wrong way round.