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Pro 97 volume problems
On Tue, 28 Feb 2006 23:56:58 GMT, "Allen Crawford"
wrote: I recently purchased a pro97 scanner in near new condition over the internet through ebay. The item was listed as having very low audio such as one has to place the speaker next to his ear to hear the broadcast so I took a chance and bought it for 45 dollars. I got it in yesterday and it is totally new! packaging, all accessories, books and not a scratch on it. Well. I unpack it and install freshly charged (new) batteries and I go to playing with it..first..a weather channel..sure enough, very low volume even when cranked to the fullest it is still at the same volume level. I went ahead and took out the four back cover screws and examined the area where the volume pot is soldered and took some readings. center tap is about 2.1kohm and 200 k ohm on the non grounded side. (this is without power applied) in the area of the volume/squelch pot, are 3 tiny pots and 3 test points...(this is all from memory as the scanner is closed up now). I was hoping for a misplaced speaker magnet or something simpler and the circuits are ungodly miniature and even the audio amp chip is about the size of an op amp on most regular size circuits. The doggone thing is so new looking, that it may be swapped with a newer one from radio shack (by swapping backplates) but I don't dare attempt the dishonest. Anyway, any suggestions to resolve my dillemma...could it be possible that I have a defective volume pot? No amount of regulation seems to affect the audio at all. The channel beep come through loud and clear but it seems that either the preamp from the radio is set too low or the pot is defective/soldered wrong. Of course, the possibility of a bad IC has crossed my mind as well. Any suggestions? No warranty so all I have is either a repairman or my good wits and some knowledge to help correct the problem. Btw, the sqelch seems to work OK. Your input would be greally appreciated, Allen Allen, I had a PRO-96 that had the *exact* same problem... I'm not sure how similar it is to the PRO-97, so the following may or may not be of any use... but might be worth a try, or may give you some ideas... Have a look at the picture at: http://www.ninemoons.com/~daf/images/PRO-96.jpg After trying all the obvious stuff, I found that very gently pushing down on the edge of the circuit board (with a non-metallic object :-) in the area outlined in red that the volome would increase tremendously. It was quite touchy, and seemed to be fairly localized to that general area. Volume would always return to it's previously "barely audible" state when pressure was released. I suspected a micro-crack in a solder joint or possibly one of the "plated-through" holes. A "cold" solder joint was another possibility... I removed the board and inspected both sides very carefully in that area with the highest power magnifier I had on hand (an eyepiece from a microscope...:-) Visual inspection didn't reveal anything, so I put the board back in and tried it again with the exact same results. This went on about 4 times until I finally got disgusted and drug out my trusty soldering iron! Having done a lot of bench work, I have a soldering iron with a tip about the size of a ball-point pin. I wouldn't recommend doing this with anything bigger, as it is very easy to overheat these SMT components. Using some high power reading glasses, I very briefly heated each of the solder joints "to melting" in the general area outlined in red, using no extra solder. (Very easy to use too much on these tiny pads!) I did add very minute amounts of solder to some of the plated-through holes until I could tell from both sides they were "soldered-through" After putting things back together - VOILA! Normal sound levels! The final test was when I could get no changes in the (now normal) volume by pushing down in area that had been so touchy before. Hope this helps... -Dan ------ Disclaimer! I'm NOT responsible if you muck things up worse!! |
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