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Author Topic: Dead Receiver???  (Read 3842 times)

Posts: 132

« on: April 24, 2012, 09:35:12 PM »

Last night I was on 40M CW enjoying a nice sked with a friend.  I decided not to use my "big rig" (a TenTec 525A) but to use my old HW-8.  The HW-8 doesn't have an accurate dial so I plugged the antenna into the HW-8 and tuned up my big 2W signal.  I used my "big rig" to help make sure I was on the right frequency.  There was no antenna hooked up to my TenTec, but I was able to spot my HW-8 and get it on the right freq.  I have done this many times and never had a problem.
This time it worked just fine.  Then I turned it off to have my chat with my friend.  About 15 minutes in we decided to QSY a bit because there was some sort of carrier that showed up on freq and made it hard to copy each other.  I decided to switch rigs and bring my TenTec into action.  I fired it up and swapped the antenna, but there was no sound over the internal speaker, I quickly hooked up my headphones, and still NO AUDIO!!!  
By this point in time I was feeling panic and dread rising up.  I finished my QSO on my HW-8 and then after tried to start over.  I checked my power supply, I checked my antenna connection.  Everything good so far.  I tuned around and saw the S-meter jumping with signals but still no audio. I tried it with headphones, with another speaker--still no audio.  The transmitter works great but no receiver audio output.

I have built crystal rigs and a DC receiver from a kit, I am getting ready to build my first regen receiver, but this little 525A is way beyond my current skill level.

Can anyone throw me an idea as to what the problem is?  And how to try and bring it back from the grave?

Tnx es 73 de KE7WAV
« Last Edit: April 24, 2012, 09:37:35 PM by KE7WAV » Logged

Posts: 6642

« Reply #1 on: April 25, 2012, 04:23:07 AM »

Sounds like the audio section of the radio failed.  I can only suggest using the headphones to try and trace where you lose it between the detector and the speaker.
Good Luck with the project!


Posts: 1757

« Reply #2 on: April 25, 2012, 04:30:35 AM »

When you say 'no audio' do you mean absolutely dead or is there some faint background hiss with the volume control turned all the way up?

It could be that your T/R relay has a bad contact in it. If that's the case, the audio chain will generally hiss a little with the volume all the way up.

73 de N4CR, Phil

Never believe an atom. They make up everything.

Posts: 2409

« Reply #3 on: April 25, 2012, 06:18:38 AM »

The receiver obviously does work as per the S-meter indication. First thing to consider is something like a mute switch or similar. Do you have a schematic? What measuring equipment do you have. An oscilloscope would be quite helpful to check the audio. I agree with the assumption that this seems to be somewhere in the audio section.

Posts: 504

« Reply #4 on: April 25, 2012, 09:15:03 AM »

Full schematic,

page 3-12 has the audio circuit.
« Last Edit: April 25, 2012, 09:42:47 AM by KB1GTX » Logged

Posts: 17483

« Reply #5 on: April 25, 2012, 10:18:59 AM »

I also have an Argosy (and an HW-8).

Do you hear sidetone on transmit?

Check that plugs #3 and #43 are properly seated on the IF/AUDIO board.
Connector #3 is the audio output to the headphones / speaker, and would make the
rig totally deaf.  #43 goes to the volume control, but the sidetone is injected after
that point so would still be heard if the plug were open.

You should hear a bit of background noise from the LM383 audio amp if #43 is open,
but nothing at all if #3 is loose.

The S-meter is audio-derived, so if it is working then you know that the signal is
getting through the audio filter to U3.  That narrows things down considerably.

So if you can NOT hear the TX sidetone, check connector #3.  By clipping a pair
of headphones to this point you can determine whether it is a problem in the
audio amp (no signal) or in the wiring to the jack (you can hear signals).  In the
latter case check for a broken wire on the headphone jack.

If i DO hear the TX sidetone, check connector #43, a broken wire or defective pot
on the volume control, or check U3 to see if one half is bad.

Posts: 132

« Reply #6 on: April 25, 2012, 08:54:32 PM »

Thank you for the posts gentlemen. 
To answer a few questions-even with the volume all the way up there is nothing; no side-tone, no hiss, no sound--its really depressing :-(
Yes I have a schematic, but I am still learning how to read them.  So its is a good starting point but I find myself having to read through a lot of Doug DeMaw articles to work, my way through it.  But this has been a good educational experience---even if it is depressing to stare at the dead rig hoping it will start to sing the sweet tones of CW back at me.
Dale--Thank you once again for all your help.  I will pop the top off the rig this weekend and see if I can find that connector and test it as you recommended. 
Thank you all and I hope to "hear" all of you on the air soon!
One thing this experience has provided me is the desire to get to know my electronics better and I think its time I begin home-brewing a few receivers and transmitters--so when they break I have a better idea of how to fix them.
Tnx agn es 73

Posts: 76

« Reply #7 on: April 26, 2012, 08:26:00 AM »

Hi i live in clinton about 50 miles south of you if you want to bring your rig over i will be happy to look at it. 73 Bob

Posts: 132

« Reply #8 on: April 26, 2012, 07:26:27 PM »

Thank you Bob I may take you up on that if I can't get it on my own.

Posts: 1757

« Reply #9 on: April 26, 2012, 08:09:18 PM »

Troubleshooting a receiver you built won't be much different than troubleshooting one someone else built unless you actually designed it.

There are several typical methods of troubleshooting.

First is to insure power supply voltages.

Second is divide and conquer

Third is working backwards from the expected output towards the power supply. This isn't a bad choice for an audio stage. Inject audio at the wiper of the volume control and see if the audio amplifier chain is working. (this is divide and conquer). If you have audio then work backwards towards the detector.

If you don't, measure voltages at the stage to see if they are all typical. Then inject at the finals to see if you have any output. If you do, inject at the drivers. If you do, inject at the first audio preamp, going backwards through the circuit.

Audio circuits are the easiest to troubleshoot in most ham radios.

You'll need an audio generator to inject audio tones with.
« Last Edit: April 27, 2012, 10:53:46 AM by N4CR » Logged

73 de N4CR, Phil

Never believe an atom. They make up everything.
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