Over the past couple of months, I had noticed some strange power output issues with my IC9100. I don’t use the radio a great deal, but at times, i would see the output power indicator drop over time, or fail to reach peak power, most noticeable on 70 cm FM, but also on HF. I checked and rechecked my antenna systems, thinking maybe the radio VSWR protection was kicking in to reduce output power and protect my device. When those checks showed my poorly built antennas weren’t that bad after all, i was at a loss. Contemplating sending the radio to Icom to check?
Next i looked at the power supply and DC system. The radio has sat on the desk since new, connected to a 60amp 13.8v power supply with the supplied icom DC cable and a quick check of the power supply showed it was still happily putting out the expected volts. The power supply has a front LED current meter in addition to the volts display, and i noticed that this was reading slightly higher than i recall it had been historically, in the 22-23amp range on TX. Where historically it had been around 20-21amps at full radio output.
Did I have a dud power connection into the back of the radio, wiggling the power connection on the back of the radio seemed to change the output power, with the radio returning to full output power and the current draw reducing, for a short while before dropping as the radio warmed up.
Back to the drawing board, was the radio broken, Did I have a faulty PA stage, related to heat, dropping back the output power. Though why did wiggling the rear radio power connector seem to make it come good for a short while before slowly dropping back the power. The last check before I found the box and sent it back to its maker was to connect a multimeter to the DC plug at the back of the radio, was the issue with the DC lead?
So the Volts at the power supply output were checked 13.82v and then the multimeter was crudely inserted into the back of the DC lead at the radio plug and the voltage measured, 13.82v on RX and 13.48v on TX at 20.5amps, and then it dropped, 12.23 v and 23.2 amps. Was it the connection with the multimeter, a wiggle and it was back to 13.48v, but it dropped again.
So i unplugged everything, removing the power cable from the DC Supply and realised the power cable had two blade fuses inline. (having been hidden behind the desk for years), i did not realise they were there. A quick check of these, and i discovered the contacts were oxidised/tarnished and (warm). The positive lead contacts had been getting very warm with use at some point and some of my input DC power was turning into heat. A quick clean and reseat/adjustment of the blade fuses and quick adjustment of the holder lugs to increase the tension, connecting the radio back up saw it seeing 13.82v RX at the rear connector, and 13.53v on TX. The current had dropped back to its expected 21amps, and after some use, a check saw no increased heat on the fuse holder. Wiggling the power cable must have been moving the fuse holder enough to make the difference.
So, if your icom radio with inline blade fuse holders has erratic power output issues, check the fuse holders and clean/reseat the fuses to ensure this is not the issue. It just might be a cheap/free/quick fix!
As an aside, i purchased two new 30amp blade fuses and popped them into the DC cable just to be sure, a couple of weeks on and i am still running at full power!