Repairing devices - test-drb@ccmp.vtda.org

30 Oct 2002

On Oct 30, 16:38, Patrick Finnegan wrote:
...
  I've got a 35mW HeNe Laser + Power supply that I
picked up today for next
 to nothing.  It seems to be having some problems - the laser (somtimes)
 blinks a few times when I first turn it on, and then stops. 
As a few others have said, most common cause of an HeNe laser failing to
"lase" is loss of the helium.  I, too, found that out the hard way.
 Interestingly, the more it's used, the less likely that is to happen in a
given time (at least, so said the notes with the last HeNe tube I bought).
...
  Now, I've never really worked on a HV power supply
before, and I'm trying
 to be careful when I play with things.  First off, does anyone have a
 general idea of what sized dummy load ("resisitor") I should try haning
 off of the HV output to properly load it?  I noticed that the laser tube
 has 3x27kohm resistors in series, would a couple watt approx 81kohm
 resistor be a good idea? 
Probably not.  Although not always obvious from the specs, most resistors
are only rated to some hundreds of volts, maybe a thousand or two.  That's
why your laser has three in series instead of one bigger one.
...
  Also, does anyone have an idea for a failure mode to
look for?  I've got
 an O'scope, dmm, and various other tools at my disposal, but no
 'authentic' HV test/mesurement gear. 
You want a proper insulated HV probe for a start...  you need to be able to
measure kilovolts if you want to check the power supply.
Check out Sam's laser FAQ at www.repairfaq.org
--
Pete                                            Peter Turnbull
                                                Network Manager
                                                University of York