Re: Toroids winding information #ubitx

Jerry Gaffke

My idea would be to divide and conquer.

First step, see if you get proper quiescent currents through the IRF510's.

Put an ammeter in line with 12v supply for the IRF510's,
turn RV2 and RV3 to the minimum setting, all the way clockwise.
Put a 50 ohm dummy load good for at least 5W (intermittent, better if 10W), on the antenna port.

Power up and hit PTT with no attempt to transmit anything, ammeter should be close to zero ma. 
Slowly slowly turn RV2 up, should be able to get 100ma of drain current on Q95 when RV2 has the gate at around 4v.
Then do the same with RV3 till we get an additional 100ma (200ma total on the ammeter) through Q94.

If you now have the ammeter at 200ma, the IRF510's are doing fine, L8 and L9 are passing current,
and traces from the 12v supply through L8 and L9 into the IRF510's are all intact.
Possible that L8 or L9 is shorted and thus zero inductance, but unlikely if not visibly damaged with obvious scorch marks.

Exactly how did he feed 500mv of RF into T10? 
I'll assume you remove R961, add a short across C92, then inject 500mv peak to peak of RF into T10 pin 4. 
If you don't remove R961 you have 12 volts DC in there, could blow out the signal generator.

All those relays and low pass filters are a major complication.
I'd cut the trace from T11 pin 5.  Easiest spot to cut would be on the back of the board, the 1 inch long trace
from the transformer closest to the two IRF510's, cut it near the transformer.  Can be repaired
later by scraping soldermask from the trace and adding a short wire from transformer to trace (or a big solder glob).
Then add a 50 ohm dummy load from T11 pin 5 to ground.

Now, with PTT pressed, apply the 500mv pk-pk of 7mhz RF into T10 pin 4.
If that picoScope can see 7mhz, should now see something on the order of 250mv pk-pk of RF centered at around 4v of DC
at the gates of Q94 and Q95.  The drains of Q94 and Q95 should now have about 2 volts of 7mhz RF signal centered on 12v DC.
(Note that the two gates have complementary RF signals, when one is high the other is low.  Same with the two drains.)
And the dummy load should have about 4 volts pk-pk on it.

The 4 volts peak to peak of RF on the dummy load would  have an rms voltage of  (4/2)*.707 = 1.414 volts,
and the power into the dummy load would be   1.414v*1.414v/50ohms = 0.040 Watts.
So the dummy load could be most any 50 ohm resistor, though a small resistor will quickly vaporize if you turn up that signal generator.
Those without a picoscope or signal generator could use a simple diode RF probe with a DVM to check the RF voltage levels,
and one of the si5351 outputs through a couple series resistors to generate the 7mhz test signal.
The diode RF probe is not very sensitive, so perhaps double all of the voltages, so 1 volt peak to peak injected into T10.
Not obvious exactly what load T10 will present (due to gate loading by the IRF510), but a couple 50 ohm resistors in series
to ground  from the si5351 should get you into the right ballpark, the junction between the two resistors gets tied to T10 pin 5.

But beware, I haven't actually done any of this.


On Sun, Feb 4, 2018 at 12:23 am, Raj vu2zap wrote:
What Cesar has not told us other than he has some great antique guns is that he has
6600 function generator. He also has a pico scope.

I've been trouble shooting via whatsapp which is faster than group emails!

The last test done was to feed 500mv to T10 at 7.15MHz and check output - NIL.
Any ideas Jerry!


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