Wednesday, May 20, 2020

IC-7800 power supply failure






I use my Icom IC-7800 only for a few contests in a year and sometime for remote operation... About 2 weeks ago I was monitoring 6m and after 4 hours the radio died. Switched off 16A fuse... 
I take it at home and called to Karel OK1CF for help. Karel told me a lot of experiences from: how many screws I have to do, to how imposible is to find schematic diagram from it etc.
Thanks a lot Karel. 

True is, that the PS is black box from Futaba, code is FP2346C. Nothing on Google. The service manual from Icom is very nice, but there is nothing about PS :( 

I started opening TRX. Compare to IC-7600, Kenwoods etc, this is really different TRX. It is almost impossible to try anything when you remove some box. You have to disconnect a lot of flat cables, disconnect coaxes etc. 

I removed a few boxes and than power supply. First look and problem found. Both mosfets + resistors in the gates grilled... +15V part was dead.
I ordered new FETs but on 99 % also the driver should be dead. Replaced and yes, no signals to gates :( I tested rest parts of the power supplies (HV, +8V and +48V). By shorting optocoupler PC5 I switched on rest parts. Fan started, +8 and +48V too. Great some good news. Than I have decided to try last thing - apply external +15V. Connected PS to TRX and bingo, TRX alived! Not nice, but better than lost full TRX.
Icom needs now external +15V and about 4A.

 Died +15V PS part
 Disconnected HV (390V DC) and connected external +15V 

 Alive!

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