You did not give an indication as to just how bad the sensitivity problem is. I have owned several of these radios and one problem experienced is that there are a number of diodes on the RF input that can blow if the rig is hooked to an antenna, while another rig nearby is operating on a different antenna (like at Field Day).
These diodes are light duty and can not take the overload. The best indication of this being the case is that some bands will give you good receive, while others seem almost entirely dead. The noise will be very low on the bands that have the bad diodes in them.
You can buy heavier duty replacement diodes at Radio Shack, but some care must be taken when replacing them, as you have to lift the RF board up and out of the chassis. There are also a number of plugs and coax jumpers internal to the 735 that must be removed and then reconnected after you have finished replacing these diodes.
Best bet is to remove and replace all of the diodes towards the back of this board. This way you don't have to try and figure out which ones are actully shot and which ones aren't. Just be careful to get the polarity correct when intallling the new diodes.
The Yaesu FT-1500 appears to have a problem with the tone encoder malfunctioning when the DC voltage to the radio reaches 14.2 volts.
I and two other hams that I know who own this radio have experienced this problem. The reports we received were that the radio dropping out of the repeater.
I discovered that when I turned the engine off, the problem went away. When the engine was running, the problem would reappear. I monitored the voltage and saw that my normal charge voltage was at 14.2 volts. The radio appeared to work OK until the voltage hit this number, then I would get reports that it was dropping out. The rig was still transmitting full power, but the sub-audible tone was disappearing at 14.2 volts.
Most late model vehicles charge the battery with a voltage of 14.2 volts and not the 13.8 volts used in years past.
WA3CVB told me tonight that he has resolved this radio cut out problem.
He bought a full wave rectifier at Radio Shack and used one of the heavy duty diodes in series with his power cable. This drops the dc voltage to the radio about one volt. This radio appears to work fine at this lower voltage.
73 to all.
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