From: user@example.net   
      
   On 10/6/2024 4:07 PM, Dave Platt wrote:   
   > In article <66f4d3b5$1$1427964$882e4bbb@reader.netnews.com>,   
   > bitrex   wrote:   
   >   
   >> Any serious gotchas/unobtainium parts with respect to repairing these   
   >> 1980s/90s(?) Branson ultrasonic cleaners?   
   >>   
   >>    
   >   
   >  From what limited knowledge I have of them, I suspect that there are   
   probably   
   > two major points of possible failure:   
   >   
   > -  The ultrasonic transducers may have reached end of life (cracked?), or   
   >     de-bonded from the steel tank.   
   >   
   > -  The ultrasonic oscillator may have failed.  These often seem to be   
   >     resonant oscillators (a suitably-chosen C, interacting with   
   >     the L of the transformer) driven from the rectified mains voltage,   
   >     with one or two high-voltage NPN transistors or MOSFETs as the   
   >     switching elements.   
   >   
   > For either of these cases, there are probably suitable generic replacements   
   > available.  The trickiest part might be removing a failed transducer from   
   > the tank, and the securely bonding its replacement (presumably with some sort   
   > of epoxy but I don't know what type).   
   >   
   > A good friend of mine had acquired a Quantrex 125-watt cleaner which wouldn't   
   > sonicate at all.  His testing showed that the two NPN power transistors in   
   the   
   > oscillator were dead... and he wasn't particularly complementary about the   
   > arrangement which held them to the aluminum bar which served as a   
   heat-sink.  They   
   > may just have overheated and cooked, after years of service, or shorted to   
   the   
   > heat-sink and fried themselves.   
   >   
   > The specific parts in question were unobtanium.  I looked around on DigiKey   
   > and found some modern parts which looked like suitable replacements... better   
   > voltage and current and dissipation ratings, similar package, and not   
   > expensive.  I included a few in my next order, and handed them to my friend   
   > along with a couple of suitable-sized mica insulators left over from my   
   > amplifier-building project.  He installed the new parts (with proper   
   > silicone grease), and the cleaner came back to life and makes plenty of   
   > cavitation.   
   >   
   >   
   >   
      
   Hi, thanks for getting back. The used unit I picked up seems to   
   ultrasound pretty good and passes the aluminum foil test, putting lots   
   of tiny holes in it...it's perhaps not in perfect adjustment but   
   probably will work well enough for my purposes which isn't much more   
   than cleaning various electronic bits, toy train parts, and maybe my   
   girlfriend's jewellery from time to time.   
      
   Heater seems bad (can hear relay switching but no heat) but that's   
   probably an easier fix, though I haven't had time to dig into it.   
      
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