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Sunday 29 July 2012

Have I killed my FT817 :-(

Right in middle of RSGB IOTA contest, well about 4am this morning. I thought I'd switch to my FT817 and new laptop. Switched on and everything seemed to be fine, was not keying anything at the time and just listening.... then buzz... psskt and the FT817 goes dead.

Immediately switch off the DC/mains feeds to anything radio in the shack.

That definitely recognisable magic smoke smell. emanating from FT817.

Quick check and nothing else effected, laptop USB ports all fine and did a visual check on the sockets etc.

When cool (it was warm) I opened to discover that a choke near the DC input has some turns that are definitely melted!

Rubbish photos right now but only got a crummy camera with me.  It is the bifilar wound choke just to one side of the L3 inductor.

Anyone had this before?

I have the RF from the active rig going through an RF sample. So that I can feed into an oscilloscope to check what the signal looks like and isn't clipping etc... that is fine.

Been told that the inductor in question is T1035.
It sometimes goes short circuit between the windings . It can be repaired by replacement
or rewinding- it is only a few turns of enamelled copper wire around a toroid. 28SWG or 27AWG or 0.4mm in diameter. Suggestion is twist up 50cms so that you can bilfar wind it through the toroid - you will have some left over. Can use the original as a guide. The wire gauge is a little light for the current taken by
the FT-817 at full blast and I surmise that the enamel gives up under the heat and you end up with a short from supply to ground. Fingers crossed no other damage to rig :-)

I might check that TP1077, TP1078 and TP1083 are not showing a short to ground with the choke not here.

Some more digging. The PSU I am using for the FT817 is a Maplin XM19V. I see 13.8V on the output between the black and red terminals but between the chassis gnd and the black terminal I see 24V (23.62V) eek! What is that there for? Anyone got a circuit diagram of that PSU?

Doing some investigation of the shack DC stuff.

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