Lars,
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Thats an interesting one.
What band were you on?
Do you know your antenna system's SWR at the operating frequency?
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On 160m and 80m, the voltages across the finals exceed the Vds spec for the BS170's of 60v,
even when operating into a 50 ohm dummy load.? It gets worse as the SWR increases.
Operating on 40m is also at risk with even a moderate SWR mismatch.
Having transmit-shaping-OFF may cause spikes, making it even worse.
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So my guess is that you have simply blown your finals again.
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Good to hear that you can talk to the processor, this doesn't sound too serious.
My best guess is that a 150ma current limit is not enough on startup when running at 7v,
try increasing that to maybe 500ma.
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At startup, the processor is running on the linear 78M33 regulator, and is drawing
around 130ma from that rail.? Since it's a linear regulator, that's 130ma straight from
your 7v supply.? The processor then starts up the 3.3v and 5v SMPS supplies.
There may be a significant surge filling up the large capacitors at C106 and C107.
Also, the rig will be drawing around 100ma from the 5v SMPS once it comes up at maybe 85% efficiency,
That's 100ma*5v/0.85 = 0.59 Watts from the 7v supply, which is another 0.59w/7v = 84ma.
The rig will be drawing a total of roughly 130+84 = 214ma from the 7v supply, plus a bit more
to deal with that surge.? Hence my suggestion that you increase the current limit up from 150ma.
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I think the solution to the high Vds seen at the BS170's is to do away with L502.
This will reduce power output, so rewind the 3:2 turns ratio at T501 with the 1:1 turns ratio
used on the 9v build.? Your post gives me reason to get back to it, and do some hardware tests.
Since the 9v case doesn't have quite such high voltages at the BS170's, probably fine to leave it as is.
Here's my old thread on this, not a lot of interest expressed and I had plenty of other things to do:
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Jerry, KE7ER
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