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Hello Jerry,

Thanks for the reply and suggestions of where to look.?? I would guess it has something to do with me feeding the ubitx microphone input directly from the line output from a C Media soundcard dongle.? I had no isolation transformer or blocking cap in between the two until I installed the EasyDigi.? SSB worked fine ten days ago, but since then, I've continued to attempt to interface the ubitx and soundcard with just a 3.5 mm stereo cable.

I haven't dropped the radio, or touched the calibration of the BFO.? I thought about reloading the configuration I've been happy with, but didn't want to unless absolutely necessary.

I've been using the radio on CW for a year now and SSB infrequently without issue.

Your comment "Applying several volts of audio to the modulator somehow, enough to blow the diodes?" is what I suspect the problem could be.? I would guess the soundcard line output is somewhere around 5V.

Karl, W5QJ

I had a chance to troubleshoot my radio this weekend, but am unable to find TP20 on the board.? I've checked everything but the voltages suggested by Jerry.? Perhaps it is clearly marked, but my 65 year old eyes can't see it.
Also, does anyone have an idea of what could be used for replacing the surface mount diode, D5?? I suspect it is the problem with the unsuppressed carrier.

Thanks,

Karl, W5QJ

Between C64 and C52 (the two large blue electrolytics on my v4 board.

Test points are not on the v3 uBitx boards, they got added with v4 (and remained on the v5).
TP20 is on T7 pins 3 and 5 at the modulator, that node goes down to the rx audio preamp and tx mike amp.
D5 is a BAT54S, a dual shottky diode in a SOT23 package:
? ??

Jerry

Thank you Jerry.? Not sure of what rev level this board is.? I've had it about a year. I'll order a couple of diodes and see what happens.

Karl

First uBitx to be sold was v3.
Mine says "uBitx v3 (c) hfsigs.com 2017" in copper on the board edge nearest the 4 relays.
Has the TDA2822M audio amp chip.
If you can't find any testpoints, it's almost certainly a v3.

The v4 was announced in late May of 2018:
? ??/g/BITX20/message/50421
Has the discrete 2n3904/2n3906 push-pull audio amp.

The new v5 has an LM386 audio amp chip.

Let us know if you figure out this unsuppressed carrier thing.
If too much audio into the mike jack can have the mike amp to blow the modulator diodes,
that's something we should all be aware of.?

Jerry, KE7ER

Jerry,

I have the v3 board as do you.? I bought 10 diodes from Mouser and installed a replacement (twice) this afternoon.? No improvement and still have the unsuprressed carrier.? I also heated up the pins on T7 to check for a cold solder joint, looked over the entire board with a magnifying glass to see if I missed something.? Loaded version CEC version 1.1 software, recalibrated, etc., without any success.

At the C50/C63 node, I am getting 1.4 mV without the microphone being keyed and 1.2 to 1.5 mV when the microphone is keyed.? I looked very closely at the microphone jack for bent pins and can't see any.

As before the radio works fine on CW and receives well.

Any other thoughts?

Karl - W5QJ

For those trying to follow the conversation, it started in this other thread:
? ??/g/BITX20/topic/30204401
Karl's adio had been working well as an SSB transmitter, but after trying to adapt it to a PC soundcard
for use on digital modes, it now has a strong residual carrier.
My understanding is that this undesired carrier is roughly as strong as the desired sideband.
Karl tried replacing the BAT54S diode pair in the modulator, that apparently did not help.

This fault may have nothing to do with the attempts at a soundcard interface,?
could just be from jostling and banging around the board.

Curious that the carrier is not getting at least somewhat suppressed by the 12mhz crystal filter.
I'd try shorting across R114 to disable the output from the modulator, then see if the carrier is still
there when the mike is keyed.? Could be that CLK0 is somehow getting coupled in after the filter.

Karl reports "At the C50/C63 node, I am getting?1.4 mV without the microphone being keyed and 1.2 to 1.5 mV when the microphone is keyed".
That node is going into the modulator from the mike amp.
Not clear if that is a DC level, or some sort of audio or RF AC.
If it's AC, that might just be local noise (perhaps from CLK0) getting picked up by a scope ground lead.
If it's DC, I would not expect that, but then I would not expect a mV or so to cause a very strong carrier.
Might be worth removing C50 and C63 from the board using two soldering irons, clean the board
in that area with alcohol in case some flux is providing a conductive path, then power up and see if
there is still a significant carrier when the mike is keyed.?
Check those caps with an ohmmeter to verify they are not leaking.

Perhaps windings on T7 have shorted out?
Might be worth rewinding T7 with new magnet wire, see if that helps.

Could replace that modulator with a commercially available diode ring mixer such as an SBL1 or ADE1.

One of the cheap AD8307 RF sniffers on ebay would be useful for looking at these?low level RF signals.?
Solder coax into the uBitx keeping signal and ground?as short as possible, run that coax into the sniffer.
? ??

Hacking at boards to investigate problems like this must be done carefully.
Would be very easy to create a second reason for this strong residual carrier.

Jerry, KE7ER

Thanks again Jerry.? Those were DC voltages as measured by an auto-ranging Chinese DVM.? The LCD display has blackened on my good volt meter.? I do have an oscilloscope, but just haven't had enough time to really look in depth.? I am looking for another microphone jack identical to the one that came with the radio, but doubt that is the issue.

The radio was never jostled around as I was simply plugging in a cable from the C-Media soundcard dongle to the microphone jack on the radio.? It could be a coincidence that things went south I suppose.? I did use this radio for a year without any issue, other than with the built-in keyer.? I've been using an external keyer for several months as I was never quite able to get the internal timing in the radio adjusted.? Much past 18 to 20 wpm, and all sorts of strange things would happen after a few minutes.? But then again, that is an entirely differently issue.

It will be this weekend before I have a chance to play with it again.

Karl -W5QJ