N75 help needed


Bill VanKirk
 

Just completed a N-75 kit and have no audio. I have checked my work, connections etc. The transmitter is putting out 5 watts with forward modulation and seems to be working fine. I can not get any audio to the speaker. I also note the AGC LED is on solid and bright in receive. Any kit builders out there willing to take a look at it for me. I would be glad to pay you for your time. I don't want to attempt anything with the surface mount parts as I am sure I would destroy the board. Can someone help me out? 

73
Bill


Curt
 

Bill

There are some clues here. Check orientation of diodes, transistors, electrolytic capacitors in the receive audio section. That led says look around there. Take a break then look around to find what's misplaced or not soldered. 

Curt


g gusto
 

Hi Bill, you can probably figure it out yourself.  Curt is right, take a break and do something else. Return later with fresh eyes.  I'll suggest get a magnifying glass and with bright light,  carefully look for any solder bridges between circuit traces especially in that RX section.  I've erred with hair thin bridges more than once!  Good luck. Let us know what you find. Gus


g gusto
 

P.S. Bill have you tried headphones?


Bill VanKirk
 

Yes I did try headphones, no joy. Using an outboard amplified speaker I can get audio off of pin 4 of U-1 and the wiper of the vol control. I have checked my work over and over several times and so far I have not found the issue. I have confirmed the caps are placed correctly as well. The only part I am not sure about is U2. The instructions are not really clear on how it should be mounted although I don't think it would have anything to do with lack of audio. I am not one to go poking around inside for fear of causing further damage to the radio. Not that is matters however I have built a lot of kits and for the most part they have worked as expected. I do appreciate the suggestions.

73
Bill

On Sun, Mar 13, 2022 at 6:12 PM g gusto <hamgusto@...> wrote:
P.S. Bill have you tried headphones?



--
73
Bill
W0PT


William Franklin
 

Hi, I'm Bill Franklin, K5WB, and I've just joined 4SQRP.  I've been a ham since 1956, worked in electronics my whole career, and still do it as a hobby.  I've made just about every mistake that can be made.  So, here are a few suggestions.  Is U1 mounted with the correct orientation?  Is U1 getting +12 vdc on pin 6 (make this measurement on the pin of the IC, not the solder pad)?  Is U1 getting its ground on pin 7 (same, measure on IC pin)?  Is there any solder flux between any of the traces associated with U1 (I have personally experienced a problem with this one)?  Possible bad IC or may be bad now if it was powered up with the wrong orientation.  Hope you can get things going.  I'm waiting for the Bayou Jumper to become available again.  

73, Bill, K5WB


From: main@4SQRP.groups.io <main@4SQRP.groups.io> on behalf of Bill VanKirk <bvkirk@...>
Sent: Sunday, March 13, 2022 6:57 PM
To: main@4sqrp.groups.io <main@4sqrp.groups.io>
Subject: Re: [4SQRP] N75 help needed
 
Yes I did try headphones, no joy. Using an outboard amplified speaker I can get audio off of pin 4 of U-1 and the wiper of the vol control. I have checked my work over and over several times and so far I have not found the issue. I have confirmed the caps are placed correctly as well. The only part I am not sure about is U2. The instructions are not really clear on how it should be mounted although I don't think it would have anything to do with lack of audio. I am not one to go poking around inside for fear of causing further damage to the radio. Not that is matters however I have built a lot of kits and for the most part they have worked as expected. I do appreciate the suggestions.

73
Bill

On Sun, Mar 13, 2022 at 6:12 PM g gusto <hamgusto@...> wrote:
P.S. Bill have you tried headphones?



--
73
Bill
W0PT


g gusto
 

Hi Bill (K5WB), Welcome to the group. I just joined a few weeks ago. With your extensive background and interest, I'll bet you will be a great asset to our club! 73 w5gus