K5BCQ click fix 2nd generation installed #ubitx

Don, ND6T

Lacking a leaded capacitor in that general range, carefully touch a wire from the top of your new C50 to the I/O trace while in receive mode. This bypasses the new board. If it restores audio then you know if the rest of the receiver is still functioning. In that case, check the gate of Q3 to ensure that it is getting the RX voltage. If it is, then either Q3 is bad, R2 or R4 is shorted, Q2 is shorted, or some unimaginable other combination of bad things.
Looking at the top of a 2N7002, with the single pin (that's the drain) away from you, the left pin is the gate, the right pin is the source.

If there is no audio  when you couple the audio past that gate then we can assume that your replacement capacitor is bad or that the receiver chose that moment to quit.

Having a little outboard audio amplifier would provide you with an excellent tool. Just a good blocking capacitor on the input will allow you to probe from product detector to speaker.


3am... you must be like me. Why sleep.

I replaced C50 with a .47U 1206 16V Ceramic Capacitor. Its was the closest I could find at my local electronics shop. Still no audio.
I'm planing to replace C63 and C250. But I need to get parts.

I do not have proper test equipment. But, I bet someone I know does, I put out the word.

If there are any additional suggestions though, they are much appreciated.


raymond bisseker <g3srq@...>

Still awaiting delivery of my uBITX....Hopefully next week?...Brilliant posts on this site...Helpful...Thanks guys.


Don, ND6T

Very well documented Patrick! The original C50 and C63 are not polarized. C250 is part of the sidetone filter and would not cause your problem, but C50 is certainly suspect. Try substituting something for C50. Anything from 0.1uF to 10 uF. If you use a polarized substitute put the positive side toward Q70 and R50.
Do you have any signal tracing equipment (tone, oscilloscope, outboard audio amp)? Those would be quite helpful at this point and would have saved you a lot of work. It appears that you have done everything properly but it is 3AM and I am not competent enough at this time to be sure. I'll keep studying your message. 73, Don


OK, I am stumped and I could use some help. For context, the issue is no Audio at all when powered on ANT attached or not.

I annotated this drawing to match my pictures.

Here's what I've tested all but the TX test was without mic attached:
  1. Rework
    • I resoldered a few wires that didn't look great.
    • I cleaned up a dropped blob of solder that was all over C250 and R251 on the main board. (oops)
      Ultimately, I had to pull C250 off the board, clean the solder off the board and reattach. The solder caps came off C250. I rebedded it in solder on the pads as best I could. It is firmly attached and continuity around it is correct. <<-- This might be it. Not sure.
    • I cleaned the board and main board anywhere I did work with rubbing alcohol and a q-tip
  2. I replaced my TDA2822 just to see and it had no change.
  3. General Continuity Tests
    • I have continuity from the outboard end of the wire (from the main board) to the next component on the add-on board (i.e., across the next trace) as follows:
      • Blue  to R5
      • Brown to R3
      • Black to C1
      • Purple to Bottom right leg of Q3 (as in drawing above)
      • Yellow to R2
      • Orange to top of Q2
    • My trace breaks on the main board are all good. No continuity across those.
    • My jumper wires at the breaks are good. Continuity across those tested across and not on the jumper wires.
  4. Power Tests (RX)
    • I DO NOT see any voltage on Blue wire to the Black wire (GND) on the board. This makes sense .. its on the TX side.
    • I DO see 12v from on the Brown wire to Black wire (GND) on the board. This is the RX side so again, that makes sense.
  5. TX Tests
    • PTT does enable TX on the display
    • PTT turns on 12V on the Blue TX wire (see above)
    • PTT turns off 12V on Brown RX wire (see above) 
  6. Speakers
    • I tested with a mono speaker that I've used before
    • I've tested with a stereo headphone that I've used before

My fear is that I've messed up the capacitors (that's what those brown things are right?) at C250, C50 and C63.

Am I correct in my sizing of these from the V3 schematic (
C50 & C63 - 1u
C250 = .1u

Am I also correct that C50 and C63 are polarized? I could have screwed that up when I desoldered them, dropped them 300 times before I barely stood them on end and tombstoned them. ;)

I'm stumped and could definitely use an Elmer.
Patrick W7PEA


Looks like I spoke too soon. When I re-assembled and plugged back in, I had no audio.
It does go into TX when I key the mic. I'm not sure if its getting out though.

So bummed, but this was my first time soldering surface mount components and I figured it wouldn't be perfect on the first attempt.

More to come... 


I didn't see pics of this in the site, so I thought I'd share mine. Continuity tests all look good. But, man tombstoning those surface mounts was hard! I Now understand why there was a REV 3. :-)