Yaesu FTM-100D NO VHF Power

A friend owns this rig. he was using it on 2 meters when it just up and died. The RF output for VHF wasn't anything that would register on a power meter although the LCD display thought everything was fine. Current draw dropped to almost RX level. 70CM output was still there at almost full power. Yaesu's technical suppliment is kind enough to provide schematics, parts layouts and tuning procedures but stops short by not providing any walkthrough of the circuit paths. I guess they figure if you're reading the supplement, you are smart enough to figure the rest out.

What I found when I opened the rig was a fried SMT coil that was no longer on its pads! It just rolled over and died. After reading what I could find on this and other similar Yaesu rigs, I made a guess at what happened.

My guess is that the relay for 2 meters either failed to close / open properly which caused an unhappy condition with the Mosfet and its driver circuit. The fact that the Mosfet final isn't shorted and produces power on 70cm has me stumpted.

In the process of replacing the three relays and the toasted L1516 coil, I found that each gate of the Mosfet final had four darkened 10 ohm resistors. I first attempted to clean them with alcohol and a Q-tip. Well that only served to lift two of the resistors off the board! This thing must have been HOT...

I'm ordering the 10 ohm gate resistors and hoping that when installed, the rig plays nice. I will update the page after they are installed.

Below are a few pictures showing the nasties in the Yaesu FTM-100.
Clicking on any pic will bring up a larger image.

The left picture shows L1516 as I found it.
Toasted and laying on its side.

The right picture is the cleaned pcb
waiting for the new coil.

The gate resistors can be seen to the
right of center at about midpoint
as well as towards the top.

The right picture is all cleaned up and waiting for parts.

Poof all three relays are gone.

Right side has them all replaced. Notice the pad on top of the relay in the middle. There is actually a copper foil tape on top of the plastic relay. The pad I'm guessing is for heat conduction, sticks to the copper tape.

I apologize for the images being flipped. I took the installed pic from an angle. If I flip it to the same view as the removed image, it looks odd.

 
K2MPW at Ya who dot com
Jan 2021