Although I have done many restorations from the 1950’s vintage Heathkit DX35 up to 1980’s vintage rigs like the Kenwood TS440SAT and Icom 735, none of them was as challenging as the FT100D circa year 2000 due to its tiny size and its use of perhaps 95% surface mount components. This FT100D came from eBay a few years ago. It worked fine at that time. After several months, 2M suddenly failed. The through hole output pin diode for 2M had failed. It fell out as two pieces when it was unsoldered,. The glass had cracked. It appeared that the leads on the part had not been spread apart enough for the part to drop in so an assembler forced it into the holes. The diode had been under stress for many years. This diode is available but it took six months to obtain one. The factory, Microsemi in Massachusetts, only makes one batch of these diodes per year. All the distrubutors were out of stock. Meanwhile, I used a lower power pin diode and kept the output power reduced. Next the 70 cm band failed, then 6M failed, finally 2M failed again on transmit. It was noticed that 6M receive is also failed although it receives well in every other band. I have been able to determine that none of the failures is related to the output power devices. For example, the HF output from the mainboard is about -5 dBm except on 6M where it drops to -40 dBm. The 2M and 70 cm signals vanish somewhere in the preamp area of the power amplifier board. Below is a photo the FT100D with its switching power supply. As may be seen above there are a myriad of flat cables and coax cables internally. Yaesu used RF connectors internally for the coax cables made by only one Japanese company, Taiko-Denki. The plug is part number TMP-K01X-A1. These have been discontinued but I was able to obtain a few samples to make the TMP to SMA cable shown below which makes it much easier to test the signal levels in the unit with a spectrum analyzer. Below is a drawing with the locations of the TMP connectors on the mainboard. The inputs are LO1, LO2, LO3, HFRX, and V/U RX. The outputs are HFTX and V/U TX. HFTX is the output for 160 through 6M, V/U TX is the output for 2M and 70 CM. Regarding the flat cables; while it may be tempting to just pull out the flat cables like a ribbon cable, these cables actually have a mechanism in the mating part on the pc boards which release the tension so the cable can be easily removed. The image below shows the connector in locked position with the red arrow pointing to the top cap that releases the cable. In this photo the cap has been lifted up at both ends as shown by the vertical red arrow. This releases the cable so it can be removed with out tension. A problem can already be seen in preparing to remove the mainboard from the casting. At the red circle on the right side there appears to be a chip capacitor that has broken in half on a daughter board in the image below.