Re: DB6NT sequencer

geoffrey pike

Hi John,
I have only SEQ2 details but they may be similar. So the gate is controlled via 3v zener. Have you monitored the gate
voltage when you let the ptt go?
Are you sure the other two IRF520s have actually failed.
Good news is that IRF520s are cheap until you find the fault.

On Tuesday, 9 March 2021, 20:32:06 GMT, John Lemay <john@...> wrote:

Hello all

I'm not having much luck lately .......

My 13cms masthead system uses a DB6NT sequencer SEQ 4 to switch a 28v
changeover relay. At the weekend I had no receive on 13cms, transmit was

Delving into the box today it seems that the switching FET, an IRF520 has
gone "leaky" between drain and source. It pulls the relay into transmit
nicely, with almost 0v on the drain, but on receive there is enough voltage
remaining to hold the relay energised.

I've replaced the FET, twice, today and failure of the device is instant but
without drama.

Disconnecting the relay from the sequencer and running the relay to an
external power supply, it switches just as it should.

Any suggestions as to the likely cause of my sequencer problem? I have just
one FET remaining ........


John G4ZTR

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