Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
NC303 Issue




 
The AM Forum
November 13, 2018, 01:49:44 PM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: NC303 Issue  (Read 611 times)
0 Members and 1 Guest are viewing this topic.
WD4DMZ
Member

Offline Offline

Posts: 97


« on: July 15, 2018, 09:29:09 PM »

My NC303 suddenly lost the ability to hear CW and SSB. Still has good AM ability and nice audio. The S meter shows SSB signals being received but no audio.

I have checked all of the tubes and find them all good. Also, tried two other 6BE6 in the BFO/product detector circuit with no luck. The mode switch looks ok as well.

It appears the PD output no longer reaches the audio circuitry.

Any ideas?

Thanks, Rich
Logged
K1JJ
Contributing
Member
*
Offline Offline

Posts: 7628


"Let's go sailing, Tommy!" - Yaz


« Reply #1 on: July 15, 2018, 11:59:21 PM »

Hi Rich,

That should be an easy problem to troubleshoot since you narrowed it down and it appears to be a broken path.

The S meter is probably measuring AGC in the I.F., so that area is working OK.  First inject an appropriate steady signal into the I.F. (or RF input)    Then use a scope to check the product detector input and output as well as the diode detector and BFO to be sure they are generating signals and mixing properly.  

If so, then it's just a matter of finding out why the path from the detectors to the audio input is broken.  Might be a bad connection, bad cap, etc.  Sometimes using a capacitor to jump across suspected open parts will find it quickly. Trace it out with a scope probe.

Let us know.

T

 
Logged

“Remember, remember, this is now, and now, and now. Live it, feel it, cling to it. I want to become acutely aware of all I’ve taken for granted.”  -  Sylvia Plath

Favorite Song - Trololo thru the years:  
https://www.youtube.com/watch?v=IVqUecYGnoM
MikeKE0ZUinkcmo
Member

Offline Offline

Posts: 308



« Reply #2 on: July 16, 2018, 06:58:33 AM »

First I'd check to see if the BFO is running, and on the right frequency, look at pin 2 of V8 with a X10 scope probe. It may pull the oscillator a few cycles but it should still sweep through the IF frequency when you rotate the CWO knob.   I would think it would either be "on" frequency, way off frequency, or not running.

Then make sure you have IF signal on pin 7 of V8.   If nothing on pin 7, look at pin 5 of V6 and see if the signal is there.

AVC/S meter signal is generated through a regular old 6al5 envelope detector.
 
Logged

Mike KE0ZU

Bold Text and PICS are usually links

https://mikeharrison.smugmug.com/
WA4WAX
Member

Offline Offline

Posts: 206


« Reply #3 on: July 16, 2018, 10:26:03 AM »

A good source.

http://wireless-girl.com/Projects/NationalNC303/
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone © 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.055 seconds with 19 queries.