Members TimBird Posted March 8, 2009 Members Share Posted March 8, 2009 Hi just got back in from a gig - using Allen & Heath mix wizzard 3 14:4:2. All seemed ok with set up then suddenly during sound check seemed to get a load of intermitent farily low frequency / static noise - bit like would get with a dirty pot on a guitar amp - being constantly rotated. Tried muting all channels, switching all other gear off one at a time, different power cables to the mixer - nothing seemed to stop it. The wierd thing is that whilst the noise was going on the mixer case seemed to be microphonic - so if i tapped it with my finger it came out of the pa. After a while of frantically scratching my head it just stopped making the noise and seemed fine - and the microphonic side of the mixer was gone. Anyway just as about to start first set - the noise (and microphonic mixer) returned - we just started the set regardless as no choice and seemed to get away with it. Whilst in the end the gig was great - it was one of the most stressful build ups to a gig that ive had - and dont fancy a repeat... Does anyone have any suggestions what may be the issue / solution ? thanks in advance Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 8, 2009 Members Share Posted March 8, 2009 There were a few with cold solder joints from early RoHS process. It's a bitch but the entire baclplane (at the very least) must be completely resoldered. I have encountered a couple of these so far, but all in all it's a tough board to beat. Do you have a qualified service tech you regularly use? Link to comment Share on other sites More sharing options...
Members TimBird Posted March 8, 2009 Author Members Share Posted March 8, 2009 Thanks for reply, Have only have the unit a couple of months (bought 2nd hand) so not had any need for engineer yet - will get onto A&H tomorrow morning and see what they recommend. Out of interest, have used the mixer about 6 times previously without any problem - any idea why we may just have experienced the problem ?(Dont really understand what a cold solder joint means as a i'm complete buffoon when it comes to technical stuff) Link to comment Share on other sites More sharing options...
Members abzurd Posted March 8, 2009 Members Share Posted March 8, 2009 Cold Solder Joints A cold joint is a joint in which the solder does not make good contact with the component lead or printed circuit board pad. Cold joints occur when the component lead or solder pad moves before the solder is completely cooled. Cold joints make a really bad electrical connection and can prevent your circuit from working. Cold joints can be recognized by a characteristic grainy, dull gray colour, and can be easily fixed. This is done by first removing the old solder with a desoldering tool or simply by heating it up and flicking it off with the iron. Once the old solder is off, you can resolder the joint, making sure to keep it still as it cools. Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 8, 2009 Members Share Posted March 8, 2009 Absurd's somments were more true with traditional lead based solders, but with the new RoHS compliant solders, the alloys are completely different and the color is no longer shiny silver but more of a dull gray, and the cold sloder joints are due to poor wicking and less fracture resistant nature ofthese materials. Extra attention to details, preheating, fulx type, solder temperature, velocity through the wave, design of the pad geometries and anular rings is critical to high quality product. We changed over all of our processes early, well before the deadline to allow us to get a jump on the rest of the market. We took our time to get it right and avoided most problems. Link to comment Share on other sites More sharing options...
Members trevcda Posted March 8, 2009 Members Share Posted March 8, 2009 Please don't "flick it away with the iron" or you cold solder joint could end up as short circuit someplace else. Believe me, this is from first hand experience! A desoldering tool, as abzurd mentioned, or desoldering braid is the way to do it. Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 8, 2009 Members Share Posted March 8, 2009 If you don't know what you are doing, you could end up with a $999 piece of worthless junk. Reworking Pb-free solder is not a piece of cake at all. Link to comment Share on other sites More sharing options...
Members 6Imzadi Posted March 8, 2009 Members Share Posted March 8, 2009 Just an observation here: Abzurd's description of a cold solder joint sound more like a cracked solder joint. My understanding of a cold solder joint is when the pad or the component lead does not reach the correct temperature to melt the solder. This causes the solder to NOT adhere to the affected surface at the molecular level and thereby the circuit doesn't function correctly.Again, this is "old school" using sn-pb solder and hand soldering methods. Andy, feel free to enlighten me on this, if needed. Link to comment Share on other sites More sharing options...
Members abzurd Posted March 9, 2009 Members Share Posted March 9, 2009 Sorry fellas, I just copied that from a "how to solder" website. Link to comment Share on other sites More sharing options...
Members agedhorse Posted March 9, 2009 Members Share Posted March 9, 2009 A cold solder joint is generally any solder joint where the crystalized structure has been disrupted or is not uniform and the molecular bond is poor. This is more common with Pb-free solders, which are an entirely different chemistry. Link to comment Share on other sites More sharing options...
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