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Author Topic: Wilderness Sierra low audio...  (Read 2497 times)
5P1CC
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Posts: 15




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« on: March 13, 2011, 10:22:17 AM »

Hello.. i bought a Wilderness Sierra some time ago at a hamfest, with the 14 mhz band module.

It worked great so far, with my indoor magnetic loop..:-)

However, after being stored away for some time some strange failure came up. The audio in the headphoneplug is very low, with the volume all the up its barely audible. 

Everything elses works perfect both  on transmit and receive...

Is this a known issue with this rig, of perhaps the lm368 audio amp ?+

73 de Claus
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NU4B
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Posts: 2331




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« Reply #1 on: March 16, 2011, 03:33:56 AM »

Hey Claus,
 I haven't heard of this problem before. It doesn't mean it hasn't happened but I don't think it is a common problem. Do you have the manual? And have you checked the voltages around U3? I'm assuming you can hear some signals (although faint) and that you have checked those obvious things (that we all forget) like headphone volume controls (if applicable), etc.. I don't know how long you had it stored away and there's always the possibility that something component failed when you turned it back on. It would be odd though. Do you have anything to trace the signal through the receive section of the rig? These radios aren't real complicated so it should be fairly easy to find where you are losing the signal (or not amplifying it).
 Also there is a Yahoo Sierra user group at  http://groups.yahoo.com/group/sierra_wilderness_radio/
 If your not a member, you should join.
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W5FYI
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« Reply #2 on: March 16, 2011, 08:06:41 AM »

One thing you might try is touching the input lead (either pin 2 or 3) of the '386 with your finger while the volume control is turned to full loud. If you hear a louder noise than you're hearing now, the trouble is not with the audio section.  If, however, the noise is quite low, one of the electrolytic capacitors at the '386 could be bad.  In that case, I'd check the one between pins 1 and 8 first, then the one at the audio output to the phones. GL
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WB8YYY
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« Reply #3 on: March 29, 2011, 09:28:59 AM »

Given the circumstances you describe, I can imagine a solder connection has broken or less likely, a tiny wire is shorting something out - if indeed it is a rig problem.  Solid state devices generally don't go bad in a short period of time being dormant. 

I would give the rig a careful visual check - starting with the antenna connector.  If you have a DVM - with no power applied you can use it to assist to make sure there is continuity where there is supposed to be.  Note that series caps will not have continuity, and neither will solid state devices.  Its not far-fetched with handling that something hasn't come loose. 

Try a substitute antenna -- like 10-20 feet of wire to see if it receives any differently.  A loss of receive gain could be anywhere!  Also check your power supply voltage.  If all truly is well with path from the antenna connector to the PA/LNA - then you can carefully transmit (for a very short duration) to see if that works - but only after you are sure you don't have an open or short in this vicinity.  Proceed with care - AND inlist a more experience local ham for help.  Often it is something simple, but not easy to find. 
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5P1CC
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Posts: 15




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« Reply #4 on: April 02, 2011, 08:34:32 AM »

Thank you very much for your help gentmen..

It was a very simple error.. the speakerjack i used shorted out the signal, and everything went okay when i switched to my headphones :-)

However, i would like to replace the final power transistor to something with a bit more outpout.. is ther a v-mos type or anything else that can be recommended..?



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