Well, never let it be said I never followed a phantom!
Just for the archive - the problem turned out to be an NPN SMD transistor on
the Receiver Control board. The job of this transistor is to assure that the
RCVR 10 volt line is piled low enough. It was open. The RCVR line was about 1.3
volts in TX, high enough to turn on the 1N4007 switching transistors in the QSK
circuit. This caused them to get quite warm on 20 meters and higher.
Replacement of that transistor cured the issues and the radio works great!
Gary
W0DVN
> On May 15, 2016, at 8:04 PM, Gary J FollettDukes HiFi <dukeshifi@comcast.net>
> wrote:
>
> I tried searching before asking the reflector for a solution to this issue,
> no luck, so, here goes…
>
> I have a Scout that works perfectly up through 30 meters.
>
> Above 30 meters, the TX power drops a LOT after a few seconds transmitting.
>
> I know why it does so. The two diodes D3 and D4 on theLLD/ALC board get very
> hot and allow TX power to leak through. This causes a pullback in output
> power as the perceived impedance of the load drops.
>
> If I lift one of the switching diodes, D3, everything is fine, full output as
> long as I want to stay keyed, even on 10 meters. Of course, there is no
> receive as D3 is the receive signal path from the antenna.
>
> My question is, does anyone know why Ten Tec chose to use 1N3007 diodes here?
> This would seem to be a poor choice as these are not particularly fast diodes.
>
> Has anyone tried PIN diodes here? If so, what type was successful?
>
> I guess I could select some but would rather benefit from others' successes.
>
> Gary
>
> W0DVN
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