Re: receive works great, but no trans power, #ubitx-help

Jerry Gaffke

I certainly wouldn't dump it.
Could sell it on the forum here.
Could state your location in the forum, see if others live close.
Could haul it into a local ham club meeting, see if anybody is 
interested in helping you debug it.
Could park it on the shelf for a week or two, then take another look.

Could be as simple as a bad connection at the antenna BNC connector.
The BNC socket provided with the kit is not machined to tight enough tolerances,
in many cases the middle pin does not make contact.
That was a problem with my uBitx, and others here have reported the same issue.
Try adding wires to go around that BNC connector directly to your dummy load.

Another common point of failure is the torroid transformers, inspect them closely.
Could be that the enamel wasn't scraped off the wire somewhere, and so the solder joint isn't working.
Or a broken wire, they are kind of heavy so rough handling while shipping can break them.
Following the schematic, check with an ohmmeter.

We should have a standard procedure for checkout out the transmitter.
Something like this:

Build a specific version of the diode RF probe, driving A7 for voltage readings to the LCD.
Create special Raduino firmware to support the debug procedure.

Set up the rig to transmit CW at 7mhz, disconnect PA-PWR to the IRF510's so they don't burn up.
Verify DC and AC levels using DVM and the RF probe at all points through T2, Q90, Q911, Q912, Q92,93,96,97.
Compare your readings with a chart for a properly functioning rig.

Apply PA-PWR, add a dummy load, measure power at IRF510 drains and at the dummy load.

Drive mike input from sidetone, go to special code that puts rig in SSB transmit mode with sidetone operating.
Verify DC and AC levels through Q6, D6, Q40,41,42, Q20,21,22
(The remainder of the transmitter was already checked out in CW mode.)

Something similar could be done for the receiver.
Perhaps generate 7mhz on CLK0 (normally the BFO) and apply that through an attenuator to the antenna port.
Trace this using the RF probe all the way through the 45mhz and 12mhz crystal filters to D5.
Now restore the BFO to 12mhz, disconnect it from the antenna, and unbalance the first mixer using CW-KEY.
Inject 45mhz at CLK2, and verify the product detector and audio chain.
Again, we need to compile a list of expected DC and AC voltages at each stage.

Parts for a good 12W dummy load (parallel four of Mouser part number 283-200-RC) 
plus a diode RF probe (1n5711 or similar, a couple caps and resistors) plus appropriate attenuators (a few resistors)
would cost about $1.  Could be included with every kit.

This capacitance meter using a Nano might also be of interest:

Am curious if anybody has a good way to measure inductance using the Nano.
I'd probably measure a 100pf cap using the above capacitance meter, then sweep a parallel combination
of the inductor being tested plus the 100pf cap using an output from the si5351 through a series resistor.
Look for the lowest freq dip using the RF probe.  Other caps such as 10pf, 1nf, ... might also be of use
depending on the size of the inductor.
The si5351 can go from about 4khz to 200mhz, up to 290mhz if pressed.

Jerry, KE7ER

On Mon, Jul 16, 2018 at 07:59 AM, Don - KM4UDX wrote:
Clark & Jerry -- thank you for the guidance! 

I think I'm getting in over my head here. I'll try some more basic debugging, but if I can't figure it out, I may have to put it in the dump and call it a "lesions learned" experience.

The ratio of working/communicating is getting way too high. I'm sadden that so many other uBitx folks are working the world, but I can't get out of my workbench. sigh. 

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