[Elecraft] K2 low voltage power down

[David N.]

Hello all my k2  has problem
Turn it on the s meter goes full up 
5 seconds later says low voltage shuts off.
I checked the display and the voltage is dropping and shut off at about 4.2 volts.
I checked at the power jack d10 and d12 and show the same thing but voltage at these points drop down to 9.4v on DVM then shuts off. Checking diodes in circuit. I cannot get a real reading check short 1 direction and chargers up in the other. The resettable fuse appears to be OK.
I tried resoldering the power, switch jacks and both diodes, to no avail.
Any suggest?
Thanks
David KR4OW