Yaesu FT-736R PSU repair
Updated for DigiKey (North American) sources & data
I gratefully acknowledge OZ1DB and his original repair documentation
and DL7VHF for his schematic diagrams
The built in AC/DC power supply on the FT-736R commonly fails after about 10 years of
normal use. The reason is usually faulty electrolytic capacitors (dried out) or bad solder joints
on the switch mode power supply board FP-1274A.
The first symptoms of the failing internal power supply are that it fails to start properly and only
a few LEDs on front panel are dimly lit. If the power supply doesn’t fail outright, the problem
ultimately leads to a rig that will not power up at all with the internal power supply. The most
likely sources of this problem are C9 (a 220uF/35 V capacitor with a defective ESR of 450 ohms
or more!), and C12 1uF/50V (with a defective ESR of 60 ohms or more). There are likely other
capacitors that are suffering from similar aging problems.
Step #1 - Remove the PSU from the main frame and disassemble the unit.
a.
unplug the AC cord;
b.
remove the radio's bottom cover
c.
remove the 3 long M3 screws from the back securing the PSU heat sink bridge plate to
rear chassis plate
d.
remove the 2 screws from the bottom side of the base (in the middle, holding the PSU
base plate on the chassis)
e.
lift out the PSU unit
f.
remove the PSU cage screws and the 4 PCB securing screws holding the base plate.
Step #2 – Visual inspection of the PSU board
The board is usually discolored between the two 470µF/200V electrolytic capacitors and
the transformer. The reason for this (and the short life of the capacitors) is two very hot
33ohm, 2W resistors (R17 and R18). See figure 1.
Fig 1. - Check C8, C9, C12 (C12 is removed here) and C22. They are likely out of spec.
