problems to get the NEScaf going
Submitted by PA0NCV on October 17, 2007 - 05:44.
NEScaf Discussion
Hello,
I hate to send you this message, but I am really stuck.
I build the Nescaf (excellent instructions) and all seems in order. IC1 is the MF10CCN.
All componebts triple checked.
All voltages are correct (8.9 and 4.7)
LM386 aplifier works fine (without IC1). starts oscilating a bit at full power, but this is not the problem.
555 generator works at 70kHz (without IC1) set at 70 whilst R10 in centre.
All R's messured at the IC1 socket are correct
Double checked all solder joins
I need to set the audio input at fairly loud to hear anything. (no problem without IC1)
Bandwith pot seems to work. Noisy on one side and quiet on the other side.
But rotating R10 to find the input audio tone does not work at all! In fact when I rotate this pot I hear many birdies just like tuning on am stations shortwave with the bfo on.
I can hear the audio tone faintly in the background but it won't peak.
Any suggestions? Could IC1 be defective?
Would appreciate any help on this.
TNX es 73,
Nick,PA0NCV
No audio
Submitted by PA0NCV on October 18, 2007 - 09:45.
Thanks Dave,
And yes Bingo!
First filter(a)was dead, second(b) worked fine.
Checked all again but without success.
Finally found it by bridging pin 10 and 11 on the IC.
No contact between pin 11 and its socket! Visually cannot see it but now that I have bend the pin a bit inwards it works fine.
Thanks for pointing me in the right direction.
Filter seems to do a nice job.
Next to get it into a box.
Cheers and 73,
Nick, PA0NCV
no audio
Things that I check (that it sounds like you checked as well)
* without the MF100. audio in to pin 19 of the socket delivers audio out of the lm386 (I specifically put audio there as it verifies all the solder connections to the lm386).
* Pins 10/11 of the socket have the clock from the 555 timer.
The MF100 is being used as two filters cascaded. If you lift the side of R5 which is connected to pin 2 of the mf100, you will essentially split the two cascaded filters. This should be the lead of r5 farthest away from the mf100. You should then be able to test both halfs of the filter.
* feed audio into the lifted r5, and it should be audible.
Please let us know what you discover.
dave /nt1u