Check for open or shorted Veractor diodes and steering diodes there may be no direct interaction as you say but if a diode is open or shorted the RF circuits might still be selected for the higher bands and the lower output power on your vhf/uhf is an indication of this. If you do not have a service manual you can get one hear, you will likely kneed one http://www.tradebit.com/filedetail.php/127575994-vertex-yaesu-ft-857-ft-857d-2005-service-repair Good Luck Best regarsds Falco
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Check for open or shorted Veractor diodes and steering diodes there may be no direct interaction as you say but if a diode is open or shorted the RF circuits might still be selected for the higher bands and the lower output power on your vhf/uhf is an indication of this.
If you do not have a service manual you can get one hear, you will likely kneed one
http://www.tradebit.com/filedetail.php/127575994-vertex-yaesu-ft-857-ft-857d-2005-service-repair
Good Luck Best regarsds Falco