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I noticed, with a new QRP Watt meter, that my SWR scans were at full power, all other performance? appeared normal.? It turned out, after a lot of diagnostic measurements, that Q507 was shorted drain to source and to gate.? Since I don't do cw I don't know if it would/did result in bad chirps.
The?AOD403 (Q507) is virtually impossible to safely remove so I clipped the gate and source leads and verified the?AOD403 had failed.?
I have a replacement on order which I will mount on top of the isolated chip.
This is a robust device that I don't see what could of killed it.? Possibly bad when originally installed.? As always possibly ESD.??
Any ideas?? Anyone else see this failure?

Hello Chris,

I have safely removed Q507 in two different rigs. ?Even though it’s a large device in close quarters, it can be removed. ?First careful remove L502. ? ?It’s best done by clipping the 2 legs then heating up the big pad with lots of flux while using teeezers to lift it out while hot. ?Don’t force it or you will rip the pads. ?Then you can heat and lift the remains of each leg after the main body is out. ?Clean up with solder wick and you can put in a new one.

Now as to why it failed. ?I doubt it was esd. ?Almost never is. ?I also doubt it was an initial failed component. ?It’s important to find out why. ?It will happen again. ?There are many possible faults in the finals section that can also take out Q507. ?That’s where I would look first.

Jeff:
I had removed L502 then I tried with my hot air station, screening off the local components but I couldn't budge it.
How did you heat the AOD402?
Earlier I had to replace BS170 after an SWR scan, in retrospect I believe it was due to scanning at 100% power.??
If in doubt blame ESD, it is very dry here!!!

I use a medium sized tip on a Hakko iron with lots of flux. ?In about 2 seconds all solder is liquified and makes for an easy removal. ?I use 750F as my temp.

Jeff
W1NC

Thanks Jeff, I'll try to remove Q507 this evening, unfortunately I will be waiting on receipt of the replacement from Digikey.
Any idea what caused the failures you see?? It seems like a voltage spike may be more of a problem than high current.

flux is key here as well as a tinned iron tip. ?If it doesn’t work right away, don’t force it. ?It should be easy.

it could be a spike or current. ?Just make sure your finals are ok and the output transformer is ok.

Jeff
W1NC