Re: uBitx v6 board failure--suggestions? #v6 #ubitxv6

Jerry Gaffke


If it's getting your goat, perhaps set it aside for a week or two.
Maybe ask for some help at a local amateur radio club.
But I think you are close to solving this.

Sounds like you have the IRF510's set to 100ma of idle drain current each, so the IRF510's are ok.
And that when you put an RF wattmeter between TP7 and ground when transmitting in CW mode
you see nothing on that meter, even when the trace from TP7 to the first relay is cut.
So it seems you are not getting RF power into the IRF510 gates from the driver stage.

Evan is right, next step is to check static voltages on all those driver transistors with a DVM when
attempting to transmit in SSB mode with no audio.  Should see the emitter somewhat above ground
(indicating quiescient emitter current) and the base about 0.6 volts above the emitter (indicating
the transistor is biased into the active region).
Here is the file from VU2ZAP:

If the static checks look ok, I suggest you next look for an RF signal that gets progressively stronger
at TP2,3,4,5,6 and the IRF510 gates while attempting to transmit in CW mode.
You could build a diode RF probe (a 1n5711 will be easier to find than a 1n34a and sensitive enough)
or you could clip 3 feet of wire to each test point as an antenna and look for it with your other receiver
(but make sure the wire is insulated so it doesn't short to something like ground or 12vdc).

Jerry, KE7ER

On Sat, Jan 23, 2021 at 05:07 PM, Evan Hand wrote:
There is a static voltage chart in the Files section of this site.  Look for an Excel file from VU2ZAP.  It is for a v4, but the RF amp sections are pretty much the same, so the voltages should be good.  The static voltages around Q90 are a good indication if the transistor is blown.

Join to automatically receive all group messages.