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Mayor513
Junior Member
Username: Mayor513
Post Number: 41
Registered: 3-2002
| | Posted on Saturday, March 11, 2006 - 2:34 pm: | 
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--Hi, all. My General Sherman AM/SSB mobile CB squeals horribly when I engage the talkback. How can I remedy this problem? First off, if anyone has questions about the install, it is in my house on a power supply, grounded properly (I mean that the PS, radio and antenna are all grounded). My SWR is about 1.2:1 or so, it is a stock radio, non export. Nothing inside the radio has ever been touched, nothing has been tweaked, tuned or clipped. So, as far as I know, it is still putting out 4 watts or so. Oh yeah, I should say that the squeal happens no matter what mike I used...Echo, stock, or Astatic 636L. Also, the Talkback on this radio is a standard feature on this particular radio, located on the switch that reads "TB/BRT----DIM".
--I have been having trouble finding any info. on this particular radio and the circuit board number (PCB = EPT0148-14Z). Supposedly, my General Sherman is a clone of the Texas Ranger TR-296, but the TR-296 has a different PCB number, so it's not perfectly exact (I am guessing). I've also been told that it is also just like the old style Cobra 148GTL and Uniden Grant XL, but the Cobra 148 PCB is PC-412, and the Grant is PC-409. Perhaps, even though these three different boards have different numbers (EPT0148-14Z, PC-412 and PC-409), they all have the same parts on them arranged the same way? It's so confusing, since I don't have these radios handy to actually look at their PCBs.
--Sorry for the long post, I just don't know much about my radio. So, does anyone know how to get in the radio and turn down the talkback volume so it does not squeal? Thanks for your help.
P.S.
The radio will only stop squealing when I turn the mic. gain almost all the way down...but by the time it finally stops squealing, I am too low for anyone to hear me. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2549
Registered: 7-2004
| | Posted on Saturday, March 11, 2006 - 3:38 pm: |
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look at the main ic chip, mayor. it's most likely rci8719. (i posted to this Q recently, & one who asked, responded it in fact was an rci8719 in their sherman). even though the board #'s differ, it is a clone of the tr296, made by rci as well. all the radios mentioned are 99% duplicates of the others. even some versions of the 148 are confused! some were made by dynascan, some by uniden, & even some by rci!!! though a same era XL & 148 are identical circuitry wise, you'll find the circuit boards are ever so slightly different. same as you go to newer versions, 296, sherman, etc. each had a tweak or 2, that may or may not have made any difference in performance. as long as it has the MB or RCI version 8719 (& NOT the MMB version or any version 8734), all the tricks work.
i never use talkback, so never really looked at it. the point at which the TB starts to squeal differs from radio to radio. a change of resistance in the talkback itself will lower its volume coming back to you, & not your XMIT audio, thereby eliminating the squeal. for a temporary fix, try an external speaker & try to move it as far away from radio as possible & see if that helps. at least you'll be able to get a feel for how you sound, & then shut off the TB til the fix can be performed. |
Mayor513
Junior Member
Username: Mayor513
Post Number: 42
Registered: 3-2002
| | Posted on Saturday, March 11, 2006 - 5:26 pm: |
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--Hi, and thanks. Yeah, it is an RCI8719. Perhaps I will just experiment with different values of resistors. I love this radio. The mic. I use is one of those inexpensive echo mics called the Superstar DM-452 which Copper sells. http://www.copperelectronics.com/cgi-bin/checkitout/checkitout.cgi?catalogSTORE:CKIE:prodE01-06013+
When using that mic., for the first time in my life, I have gotten reports of good sounding, loud audio, and with the slider on the microphone right on the first dot, it sounds great. Great mic. |
Patzerozero
Senior Member
Username: Patzerozero
Post Number: 2550
Registered: 7-2004
| | Posted on Saturday, March 11, 2006 - 6:37 pm: |
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i laughed when i 1st saw that $16 power mic, then when i bought one, i felt like i was holding a brick. i don't use it much at all, but i gotta say, it is a pretty good mic in any price range! |
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