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SB2 not working, suggestions?

Gil
 

Hello,

I just finished my SB2 and to my dismay, it does not quite work... If you guys could steer me in one direction or another...

The screen turned on fine, I selected 40m. The speaker is hissing but there is no reception (I transmitted from another radio). Trying to transmit in SSB The TX LED turns on but there is no modulation, though that could be a microphone issue... In CW I do get output power but no sidetone in the speaker, though I hear the tone on a separate receiver, albeit sounding a bit "hissy." Where should I look? The only difficult parts for me were U10 and X7. I don't have a scope.
Thanks a lot!

Gil.

Steven Weber
 

Standard suggestion check the soldering. Side tone gets sent directly into the audio amp. Check that the trimmer is in the right way and is making connection. 

Since CW works, look close at the audio stages. Make sure the AGC is not muting the audio. 

Any voltages way out of whack? 

Steve 

On Sun, Apr 14, 2019, 11:12 AM Gil <gil@...> wrote:
Hello,

I just finished my SB2 and to my dismay, it does not quite work... If you guys could steer me in one direction or another...

The screen turned on fine, I selected 40m. The speaker is hissing but there is no reception (I transmitted from another radio). Trying to transmit in SSB The TX LED turns on but there is no modulation, though that could be a microphone issue... In CW I do get output power but no sidetone in the speaker, though I hear the tone on a separate receiver, albeit sounding a bit "hissy." Where should I look? The only difficult parts for me were U10 and X7. I don't have a scope.
Thanks a lot!

Gil.

Don, ND6T
 

Use your ohmmeter to be sure that your IC pins make connection to the pads. On U4 be certain that pins 6,7, and 8 are solidly grounded. Check continuity between U4 pin 4 to U2 pin 6, U4 pin 15 to U3 pin 6. That sort of thing. Appearances can be deceiving (close does not count) and a glob of solder on a pin may hide a poor connection beneath. Place one probe on the part of the pin where it exits the IC package and the other pin on a pad connected to the pad where your pin should be soldered (another component on the same trace).

Visually inspect your solder joints. A good connection will have a visible fillet, showing that both the pad and the component (pin or face) are properly wetted with solder.

Going in to a trouble-shooting project I usually use a signal injector and start in the middle of the signal flow, dividing the problem in half as I go. My favorite injector is a multivibrator operating at audio frequency and having fast rise-time square waves. This provides audio through VHF signals to be heard in the audio output. Costs about a dollar to build. When you find a dead stage, check the voltages and then start checking continuity as described above.

73,
Don

An oscilloscope is handy and fast but nothing beats a DMM for getting it done. Just take your time and be patient.

Gil
 

Thanks guys, I will get back to it..

Gil.