[1000mp] Unexplained Final failures in Yaesu and Icom and Kenwood HF transceivers

[Roy Westra]

I used an old transceiver to log the settings for the tuner that way I can
pretune before I transmit the Mark V, I thought maybe you had something a
little more technical than a noise bridge

On Tue, Feb 21, 2012 at 11:13 AM, <rick.moskovits at ns.sympatico.ca> wrote:

> I use a tuner tuner noise bridge  to tune tuner without putting any power
> into finals-also shows antenna short or open--really saves those finals!
> Sent wirelessly from my BlackBerry device on the Bell network.
> Envoyé sans fil par mon terminal mobile BlackBerry sur le réseau de Bell.
>
> -----Original Message-----
> From: Roy Westra <rpwestra at gmail.com>
> Sender: 1000mp-bounces at mailman.qth.net
> Date: Tue, 21 Feb 2012 10:53:49
> To: All about Yaesu 1000mp<1000mp at mailman.qth.net>
> Reply-To: All about Yaesu 1000mp <1000mp at mailman.qth.net>
> Subject: Re: [1000mp] Unexplained Final failures in Yaesu and Icom and
>  Kenwood HF transceivers
>
> I have had the finals in my Mark V blow twice, we believe the culprit was
> my Palstar AT2K antenna tuner, since I had the shunt board replaced in the
> Palstar tuner I have had no problems. However I am gun shy every time I
> tune, do you have a way to protect those expensive 200 watt finals ?
>
> Roy
> AA6QQ
>
> On Tue, Feb 21, 2012 at 10:48 AM, Russell Sherry <rsherry46 at hotmail.com
> >wrote:
>
> >
> >
> > Unexplained Final failures in Yaesu and Icom and Kenwood HF transceivers
> > After 10 plus years of operation my FT 1000MP MK5 (200 Watt) had a final
> > failure. After diagnosis and the determination that the failure was not
> > explained some six months later there was a second failure. At this point
> > additional thought was given as to the actual cause and future prevention
> > of this type of event. Output power at the time of both events was 70
> watts
> > operating in class AB1.
> > Typical HF solid state transmitter topology uses a transistor amplifier
> > followed by a bank of relay witched low pass filters that is followed by
> a
> > VSWR detector. That detector is also used to control forward power. VSWR
> > shutdown is done through the ALC circuit in the transmit IF amplifier.
> > When a lowpass filter selection relay is open and there is no load or
> > antenna connected to the power amplifier (PA) and drive is applied to the
> > PA high voltages are generated at the drain of the PA output transistors.
> > This is especially true if the output selection relay in the two relay
> > lowpass filter selection circuit is the one that is open. The reactance
> of
> > the filter components generates high drain voltages. Since there is no RF
> > going to the VSWR  and forward power detection circuit because of the
> open
> > relay the ALC signal is not reduced and maximum drive is applied to the
> > gates of the PA transistors. The high drain voltage along with the high
> > gate voltage from maximum drive causes a drain to gate short in one or
> both
> > of the output FETs.
> > This is what in my opinion causes many unexplained final transistor
> > failures.
> > Prevention of final failure is done by placing a DC voltage and current
> >  through the low pass filter relay selection contacts in such a manner
> that
> > when a relay or other component such as a connector or cable connection
> is
> > not present transmission is prevented. This is done through using the
> VSWR
> > shut down of the ALC input to the transmitter IF chain. This DC
> supervision
> > is done automatically and happens before any RF is applied to the PA
> > transistors preventing them from being damaged.
> > To find out about how this is very simply done contact me at
> > rsherry46 at hotmail.com or my present QRZ email address and I will provide
> > you with a PDF file including pictures and schematic for the
>  installation
> > of this modification in an FT 1000MP MK5.
> > This solution is also applicable with modification to Icom and Kenwood HF
> > transceivers.
> > Russ Sherry, NM6DX.
> >
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