Yaesu FT-100

[N4JOH]

I have a Yaesu FT-100 that is doing the following

The unit is serial number 9F041452.

The unit appears to be in excellent physical and electrical condition
and I don't think it has ever been opened by anyone. It has never been
back to the factory for service that I know of.

The problem has been observed only on the 50 Mhz band. The unit has been
operated extensively on the 144 and 432 Mhz bands but not hf.

The unit appears to be breaking into oscillation intermittently. Under
this condition the output power control on menu 22 has no effect and
there is a high indicated SWR, which most likely means that it is
oscillating out of band.

The problem does not occur on a dummy load, nor does it occur on most
antennas with a good match. My own FT-100D operates normally on the
antenna in question and the antenna in question shows an SWR of 1.2:1 at
the operating frequency.

The supply voltage at the back of the radio is maintained at 13 Vdc,
dropping from the 13.6 volt supply through the power cord. In other
words, I think the power drop is normal and the voltage is adequate for
the unit to operate properly, otherwise.

All jumper coax cables and power meter have been changed with no effect
on the problem. The problem appears to be strictly associated with the
radio.

I recall that early FT100's had an instability problem in the design of
the SWR detection circuit that resulted in unstable operation of the
final amplifier stage of the Ft-100. Perhaps this is the problem.


Is there anything else anyone would recommend to do before we send this unit
back to Yaesu/Vertex Standard for service?


Thank you,

[W8OB]

I cannot for the life of me remember the url of the website but do a google search on the ft100 you will find a website with pictures that addresses the high swr problem found in some of these rigs. My suggestion is to do this mod the easy way. instead of the copper strip use desolder braid and tack solder it to the points indicated on the web site then to avoid drilling and taping holes in the radios channel run the braid to the center cover screw, take the screw and make sure and remove all the black paint from the bottom side of it untill its shiny. ( I used a dremel tool and wire brush). Make a small split in the braid around the screw hole so when you mount the cover the screw passes through the braid. Also shine up the bottom of the cover in the screw hole area. As a finish touch apply a light bit of solder to the braid to keep it stiff and prevent bouncing around if your going to use the rig mobile. This form of the mod will work just as well as the listed one with one exception you can remove it with pretty much no-one ever being able to tell it was done in the first place. While your at it look at the cooling fan mod on this site as well, for my rig I simply left the fan on high speed all the time. good luck Before you go through this I would suggest triple checking your 6 meter antenna system to make sure there is not a problem there.

[KE6VG]

I did the SWR mod on an FT-100 that I bought used. I had the high SWR problem on 440 and 10 meters. Aparently it appears on different bands for different people. When I had it apart I added the 500hz CW filter. Now I know why there are so many CW filters for sale used. (tight fit not the faint at heart) - I love the radio, it works perfectly now. It's a great little performer - Go to http://www.k0lee.com/ft100faq.html and read all about it.