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Hey, guys!? Relatively new ham here, this is my first CW rig - I rather ambitiously tried to build a BitX20A kit previously, but I'm still debugging it.? I jumped on the QCX as a simpler to build kit that could get me more practice at building and testing and also get me to learn CW.? The good news is that I'm making definite progress learning CW using my QCX as a practice keyer, the bad news is that I've hit a snag - I think I cooked my audio amplifier.

When I first assembled the kit everything was working great.? I put it together in a small Hammond box since my ultimate goal was to use it as an ultralight SOTA rig.? I learned from my last build that I always seem to end up taking apart and reassembling my radio for troubleshooting and repair, so I decided to build all board connectors with Dupont connectors and header pins like the LCD screen uses.? This certainly makes casing and uncasing easier as I have to work on things, but unfortunately due to the cramped conditions in the case, I ended up bending one of the leads to the headphone jack and actually shorted it out completely.? Now, I get no sidetone or band noise.? I get a click and a quiet hiss on key down, so I have still been using it as a CPO, and tx still seems to work fine into my dummy load, but I can't hear anything except occasional interference from my cell phone when it's nearby.

I'm not sure if I cooked the IC, or maybe I did something to cause the TX mute switch to stick on, or maybe I damaged a different component.

The following are the voltages on IC10 in rx mode:

1. 5.81

2. 5.81

3. 5.81

4. 0

5. 11.56

6. 5.81

7. 5.77 (buzz when measured)

8. 5.77

I can't seem to find pin 8 of IC 10 in the circuit diagram, so I don't know where to start on tracing why it has low voltage.

I also looked at the audio ch 1 and 2 in the test equipment menu.? At key down in practice mode, I get a bit of noise on Ch 2 (10 to 5), and I get a brief spike and then nothing at all until (oddly) I exit the menu and re-enter it - Then I can get another spike.
All of this was in practice mode.? Interestingly, if I turn off practice mode, I get a mot more noise on Ch 2 (150 ish) and steady slight noise on Ch 1 (around 3)

Hope this wasn't too much info, but I wanted to err on the side of doing my research.

So what's the diagnosis?? Gather more data?? Replace IC10?? Something else?

Thanks,
Jake
KE0GYC

The schematic shows IC10's output (pin 1) connects to an electrolytic capacitor before connecting to the earphone jack. So even if you shorted the audio jack pins to ground you shouldn't have killed the IC; also it's reading close to what's listed in the assembly manual (image below). It looks to me like all the Op Amps connect pin 8 to +12V and pin 4 to ground. (see schematic

Just a thought but are you counting IC pins correctly (see below)? That would account for the odd voltages you're getting.

If the earphone connector is damaged then you might be better off getting it off the board and wire an external earphone jack. If it's still in circuit it could be the cause as you why you're not hearing anything.

I hope this helps!?

--Al
WD4AH

--------------------------------------from your post ----------------------------
You measured the following the voltages on IC10 in rx mode:

1. 5.81

2. 5.81

3. 5.81

4. 0

5. 11.56

6. 5.81

7. 5.77 (buzz when measured)

8. 5.77

-----------------------------------------------------------------------------------------
? ? ?? ?

I believe you're right - I think I wrote down pins 5,6,7, and 8 backwards - 5=8, 6=7, etc.

The earphone jack is already externally mounted to my case. ?I'm getting a bit of a pop and hiss on key down, so I know something is getting through, but not much. ?I'll check continuity to the board when I get home in case there's internal damage to the jack.

The continuity of the connector seems fine.

I rechecked, and pins 6 and 7 of IC10 are still showing a bit high - around 5.7 volts each, all others seem normal.

Does the info from the audio ch 1 and ch 2 point to an audio amplifier issue of some kind?? The manual says Ch. 2 is the audio amplifier output and Ch 1 is the output of the phase nulling circuit, and seems to hint that Ch 1 is at least one of the inputs to the audio amplifier.? I'm getting normal readings on Ch 1, but Ch 2 is showing nothing but a brief pop.

Image is taken from the manual. From the looks of it pretty much a straight forward audio amp all the way back to the Volume control. The TX Mute Switch looks like it's supposed to short the audio path to ground during transmit. It sounds like it's supposed to reduce click and only operates briefly. Maybe in your case it "on" all the time and shunting audio to ground?

I'm not sure what you mean by Ch 1 and Ch 2. You may be referring to sections A or B?

One suggestion is to remove Q7 and and see what you get on Receive. You should also be able to put a finger on the wiper of the Volume control and hear a very strong hum/buzz in the headphones.

Another approach would be to use another audio amp connected to the "high" side of the Volume control and see if you hear static.?

Again, good luck!!

--Al

I replaced Q7 with no change, unfortunately.? It did look damaged on closer inspection - One of the corners looked like it had chipped off somehow.

When I'm referring to Ch 1 and Ch 2, I'm referencing the audio channels in the Test Equipment menu - Page 102 in the manual.

I looked at the schematic, and on a hunch checked the volume pot.? Not sure how, but somehow it seems to have gone out - I shorted two of the volume pot pins to check and got a tone.

Next time I go out I'll get another volume pot and see if that resolves everything.

Thanks!