DanSteely Posted December 13, 2012 Share Posted December 13, 2012 Hi, In my office I have a two PC's, a tuner and a CD player connected to an amplifier and speakers via a small Behringer MX1602 mixer - which has been barely off in 15+ years.. All has been good for a many years except I now am noticing mains hum coming through when the faders are all off at infinity. The mixers in-line mains power supply outputs AC so the rectification, regulation and smoothing is done in the mixer and the top right side where the power comes in has always run very hot. So hot in fact that you can't keep your hand on this part for longer than a few seconds. So my assumption is that over time this heat has dried out the electrolytic caps and this has led to the hum. I have not taken the cover off the mixer but wondered if you had any thoughts on the fault and if I am looking in the right direction regarding a fix to the hum... Many thanks. Link to comment Share on other sites More sharing options...
Bobbsy Posted December 13, 2012 Share Posted December 13, 2012 Before I even got to the end of your post my instinct was dried out electrolytics--it's a pretty common fault. Frankly, if you've got 15 years out of a Behringer mixer, it owes you nothing. If you have the time and inclination to open it up (and on a Behringer that will be major surgery) you could try replacing all the caps. However, if you value your time at more than a few pennies per hour, buying a new mixer might be the more economical option. Link to comment Share on other sites More sharing options...
DanSteely Posted December 13, 2012 Author Share Posted December 13, 2012 Hi Bob and thanks for your reply.. I'm looking at a few small jobs for the Christmas break and this might be one of them. The older Behringer stuff was not too bad and could under the right circumstances run for years. The hotplate feature though should never have emerged from prototyping - what prototyping you say... If you were repairing, would you replace the channel electrolytic's as well as the PSU ones? Link to comment Share on other sites More sharing options...
DrV Posted December 13, 2012 Share Posted December 13, 2012 I , similarly got as far as "humming" and "15+ years" and thought "dried out electrolytics. I wouldn't bother with any of the signal level ones unless they are showing signs of leakage, but the caps in the PSU are probably down to a fraction of their initial capacitance, especially if they have been cooked by a nearby regulator. Get some 105 degree rated ones and the PSU, at least, will give you another 15 years. Dave Link to comment Share on other sites More sharing options...
howlingwolf487 Posted December 13, 2012 Share Posted December 13, 2012 Hi, In my office I have a two PC's, a tuner and a CD player connected to an amplifier and speakers via a small Behringer MX1602 mixer - which has been barely off in 15+ years.. All has been good for a many years except I now am noticing mains hum coming through when the faders are all off at infinity.When you unplug all inputs from the mixer, does the hum remain? Also, can you describe the wiring and I/O types you are using (star-quad mic cable w/ XLR ends, etc.)? Any new gear added onto the circuit could cause similar issues, too. I tend to agree with the others, but an exercise in troubleshooting is always a good way to stimulate some synapses. :-) Link to comment Share on other sites More sharing options...
DanSteely Posted December 15, 2012 Author Share Posted December 15, 2012 Hi Guys, I swapped the humming mixer for a tiny mains powered Alesis mixer and the humming disappeared. Along with your comments, this was the proof I needed. I then decided to take the Behinger apart and had to de-solder 3, what look like voltage regulators in order to release the PCB - There was no way round it.. One of the reg legs has fractured and therefore need replacement along with the caps.. (And thinking ahead it seems pragmatic to have 3 new reg's to hand when it comes to reassembly) I have been looking on the www.rapidonline.com for the bits and have found all the caps but need a recommendation on equivalents on the regs, which are labeled: 317JRCM6116F ML7185A ML7915A I have Google'd the above numbers but am a bit snow blind by the results and don't want to ###### it up. If possible I'd like to try and get all the bits from a single supplier - like Rapid. A bit of a Sat morning time waste I know but Radio 4's on, I have a cup of tea to hand and can smell the Christmas tree downstairs.... Small pleasures... Many thanks and seasonal best regards..... Link to comment Share on other sites More sharing options...
Brian Posted December 15, 2012 Share Posted December 15, 2012 317JRCM6116F A variable voltage 1A regulator, something like an LM317 will do as a replacement. ML7185A Typo - should be ML7815AAny 1A +15V regulator in a TO-220 case will do. ML7915A Any 1A -15V regulator in a TO-220 case will do. Let us know your preferred supplier for spares and I'm sure we can dig out order codes for you. Link to comment Share on other sites More sharing options...
DanSteely Posted December 15, 2012 Author Share Posted December 15, 2012 Many thanks Brian, I plan to use Rapid for the bits... Link to comment Share on other sites More sharing options...
Brian Posted December 15, 2012 Share Posted December 15, 2012 Rapid order codes... LM317T - 47-3318L7815CV - 47-3295L7915CV - 47-3301 ...before you order just check they look the same package. Link to comment Share on other sites More sharing options...
DanSteely Posted December 15, 2012 Author Share Posted December 15, 2012 Thank you so much - you're a star. Best wishes. Link to comment Share on other sites More sharing options...
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