The OmegaForce S454HP's are notorious for certain problems. There are some batches that suffer from very poor factory quality control, which shows up as poor solder joints and some improper wiring of the RFX75 module. I own an 'S45HP, and am familiar with most of the issues. The first thing one needs to do is go into the radio and carefully look for bad solder joints. This bad soldering comes from improper use of RoHS compatible solder and insufficient or improper heat. Carefully go over every suspect solder joint. There is another issue with the RFX75's: incorrect connection of the main +13.8 V input. On some radios this wire was incorrectly attached to a diode (protection diode?) which did not deliver enough voltage to the RFX75. This was changed to connect to proper 13.8VDC, and the output went up to proper full power. Also, make sure that the mic connectors are tight and secure. You may have to add a ground braid to the shell of the connectors to make a good ground. This should eliminate some hum issues.
Finally, there are some batches of radios, with poor internal grounding (due to bad solder joints) that exhibit microprocessor glitches that cause weird and unexpected symptoms, lock-ups and other odd problems. This sometimes requires going in and resetting the uP. Correcting the solder joint issue should cure this. As well, always make sure that the radio is connected to a DC supply, to allow static to drain away. Occasionally the uP will glitch anyway, but that is rare.
Once all the bad solder joints and ground issues are addressed, the radio should work like a champ.
