Yeasu FT990 Problem at G4GYS

My Yaesu FT990AC would intermittently stop working. The S meter light would illuminate but no display and no sound. Also the memory would be lost. Seemed like a power supply fault. Reference to the circuit diagram pointed to a failure of the 5 volt line which is derived on the regulator board. The problem turned out to be dry joints on the 5 volt regulator. The following procedure . may assist others having this problem.

Ensure the mains supply is disconnected
Remove the bottom cover. Remove the masking tape securing the thin wires under the PSU. Carefully snip and remove a few cable ties. Remove the four screws fixing the PSU to the chassis.


Slide the PSU out a little. Making a note of the connections, unscrew and remove the four large terminals, and unplug connectors as neccessary. Now ease out and remove the power supply from the chassis completely.


Remove the four screws securing the regulator heatsink to the PSU.
Do not attempt to remove the board from the heatsink because the regulators are secured with clips on the edge of the heatsink.
The position of the 5 volt regulator is arrowed. The close up shows the three fractured solder joints. These were re-soldered and the parts re-installed in the chassis. The fault was cured.