On Wednesday, May 09, 2012 11:40:31 AM Ralf Mardorf did opine: > On Tue, 2012-05-08 at 12:47 -0400, gene heskett wrote: > > I hope I helped. > > You confirmed that it's a good idea to replace the capacitors, regarding > to the age of the PSU. Yes, you helped. > > Btw. the capacitors I unsoldered where still perfectly ok. > Not all capaictors are tested but we guess all are still ok, we anyway > will replace them. > > We needed a good magnifier to see that a diode (IIRC near the > opto-coupler) had a could solder point. I couldn't see it with the > magnifier I own. Could=cold=microscopic crack in the solder? > The main issue seems to be that one HER 300 (a 50 ns fast diode) for > rectification on the secondary side is borked. > After we found out this, we found out that the Behringer UB-SPSU2 is > known for this issue. Btw. it's also possible to get the circuit diagram > in the Internet for free. > > The diode does cost nothing, but it's not easy to get here. No equation > diode. We found out that there's one diode IIRC >= 3A >= 200V <= 50ns > does exist here, Thomas anyway will order a HER 300. I didn't find it at > my dealer. So no mixer today, I need to test my Ubuntu Studio by > directly connecting to the Amp or using the headphone output of the RME > card. I'm not familiar with that particular diode. However power rated switching diodes that fast really stretch the limits of the technology, so I would expect a higher failure rate for that compared to the 3 to 20 microsecond recovery times of a more normal power diode. This recovery time can result in some interesting side effects, which has nothing to do with your problem. Back in the 70's, I was a tx supervisor for the Nebraska ETV Commissions KXNE, channel 19 site in northeastern Nebraska. A GE transmitter, rated at 30kw out, it used a pair of Varian 4KM100LA klystrons for final amplifiers. Those things are hungry, needing about 19.5 to 20 kilovolts at about 10 amps to run both of them. 20kv*10 amps is 200 kilowatts every hour its running. The supply was a triplet of 240 volt out, 14.4 kilovolt, 75kw rated line powerline distribution transformers running backwards, which fed a 6 diode full wave bridge. Each of those 'diodes' was actually about 60 std DO-5 diodes in series, with a small capacitor and a small resistor across each one to equalize the reverse voltages when they were off. But those old diodes had about a 20 microsecond turnoff time, so there was 6 spikes of time during the ac cycle when the still turned on diodes caused a very effective phase to phase short for that 20 microseconds. That was relatively minor, but when they all finally turned off, the spike on the powerline was a sight to behold. Coming out of every wall socket in the building was the usual 124-127 volts ac, but superimposed were these voltage spikes about 5 microseconds wide, and as much as 3 kilovolts peak. Light bulbs and small equipment fuses didn't last as long as they should have for obvious reasons. > A note. Thomas has got best equipment from Weller for unsoldering and > soldering, but even he had issues to unsolder and solder. He was near to > take it along to his employment to do it with hot air. > It's possible to do it with my Ersa C25 and a soldering tip that doesn't > cause tinder, but since it's even hard with best Weller equipment for > somebody who does such work everyday, it's no fun to repair the PSU. > > Thanks, > Ralf > > _______________________________________________ > Linux-audio-user mailing list > Linux-audio-user@xxxxxxxxxxxxxxxxxxxx > http://lists.linuxaudio.org/listinfo/linux-audio-user Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> The human race is a race of cowards; and I am not only marching in that procession but carrying a banner. -- Mark Twain _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
