Yaesu: FT-900 will not power up.

[rbaldwin35]

Picked up FT-900 that would not power up.

So far I have found a blown trace in the PA from 13v to the connector that connects to the control board.
On the control board, first thing I saw was C277 blown that made burn marks on the back panel.
Both the 5V and 8V regulators were bad.
D3051 shorted, D3055 open

After fixing all that I now have 5V and 8V out of the regulators.
5V to pin 59 of the CPU.

When the power button is pressed, get 5V out of pin 50 of the CPU , but nothing out of pin 58 which should send the signal to close the relay on the PA board.
Checked Q3005 and Q3002 and they are ok.

Unit draws about 400ma and when the power button is pressed it jumps to 700ma then goes back to 400ma.

Not sure what I'm missing to get the radio to run on.

Any thoughts of what to check next?

Thank you

Robert
KO5MO

 

[RFI-EMI-GUY]

Not sue this will help you. I have a japan market radio that was gifted to me that powered up but would not TX or RX. (VCO Unlocked if I recall) I traced it to a negative voltage regulator (-9V) inside a can on the main board. Bought the part but never completed the repair. Also looking at my notes there was some TSB regarding a failure of a diode, likely Shottky, due to over current.