This 2004 eHam.net Q&A about K1MCN issue should assist your FT-726R troubleshooting and repairs.http://www.eham.net/ehamforum/smf/index.php?topic=55560.0
I have a Yaesu FT726R that the VFO dial dosn't work when the unit is cold. After it warms up for a while, the tuning works fine. I have isolated the problem to the control board. Is it possible that a capacitor or resistor could be cold sensitive? I have never run into this problem before.
A copy of the Yaesu FT-726R Service Manual, parts list by module and schematics are mandatory for proper disassembly and repairs.
Pete, K1ZJH offered this comment in 2004:
Erratic VFO tuning for the FT-726R really requires the use of a dual trace scope to look at the phase relationship and levels coming from the shaft encoder.
I've gone through this problem on two different FT-726R transceivers, and the most common cause is the 100pF disc ceramics used to filter the encoder noise become leaky. This is easily seen when scoping the encoder signal--the bad signal will be much lower in amplitude.
The debouncing circuit uses high megohm resistors and a small amount of leakage in the 100pF caps will kill the encoder output.
Unfortunately the capacitors are extremely tiny, and that area of the control board is densely packed! But, it can be done. I suggest using SMD replacements, right on the foil pads.
K5DOG offered this solution in 2004, which solved his issue.
For those searching for answers to this issue, I want to say that I just fixed this problem by replacing the 100pf capacitors (4) on the Control Unit Board.
They are C15, C20, C21, and C22. This replacement fixed the issue.
Remove FT-726R top and bottom covers, then remove two side screws, and the front panel swivels down out of the way. The Control Unit board is behind it. Carefully loosen the connectors and the Control Unit board slides up and out of the radio. The 4 capacitors are on the end, near the battery.