7 Nov
2002
7 Nov
'02
4:55 a.m.
I checked around but I can't find any info on this model laser. Is there a date on
it anywhere? Here
<http://www.spectraphysics.com/products/cld_products/stabilite_series.html> is a
link the the Stablite lasers on Spectra Physics website. There's also a phone number
on that page. I would call them and get the specs for that laser and ask (1) if it's a
hard sealed laser (2) if that's the right power suplly for it. Someone clould have
just stuck any power supply with it and the wrong PS could certainly cause the problems
that you're having. If that is the right PS ask them what the operating current,
trigger and operating voltage should be.
Joe
At 10:07 PM 11/6/02 -0500, you wrote:
On Wed, 30 Oct 2002, Joe wrote:
Hi Pat,
I'm assuming that your laser is helium-neon laser. If so, then if
it's 23 years old it almost certainly has what they refer to as a
soft seal between the electrodes and glass tube. The problem with the
soft sealed lasers is that the helium atoms are small enough that
they slowly leak out of the seal. When they do, the mixture ratio
changes and the ignition and operating voltage goes up until the
laser will no longer operates. That's what it sounds like is
happening with your laser. Your's sounds like it's it border line in
that the PSU firing voltage can make it fire but the operating
voltage isn't high enough to keep it operating.
The laser is a Spectra Physics Stabilite model 24B 35mW HeNe laser, and
the power supply is a Spectra Physics Laser Exciter model 255.
That seems accurate. I've rigged up a 'line conditioner' to give me a
cheap pseudo-variac to change the input voltage to the laser power supply
(the supply is a simple transformer -> rectifier -> capacitor type with a
current regulator stuck on it, here's a PDF I found:
http://www.repairfaq.org/sam/255apsch.pdf
Does anyone know what the specs are on that transformer (eg rated output
voltage), and how far I can (fairly-safely) run it above its rated input
voltage? Specifically, it'd be nice to know an upper limit so I don't
explode the HV caps or diodes.
Further you can't just use a resistor as a
dummy load. The laser
tube is similar to neon and floresent lights in that it has a
negative resistance. That is it has a certain amount of resistance
until it fires and then the resistance decreases dramaticly. You
have to use a ballast with such devices or else the current will
increase drasticly and almost instantly burn out the device. The
ignition voltage will be on the order of 20,000 volts but the
operating voltage will be roughly 12,000 to 14,000 volts.
By looking at the schematic I linked above, it looks to run at a lower
voltage than that, but it's hard to tell without a HV meter or knowing
what the tranformer is outputting.
Be careful using a scope around these things.
It probably isn't made
to handle nearly the kind of voltages involved in the laser. You
need a good high voltage probe for checking these things. You can
use one made for TV repair. They're fairly easy to find and are
reasonably priced.
I wasn't going to scope the HV side, and since there is no LV side of the
power supply, I'm just not going to bother looking at it with a scope.
Besides, it's a simple enough circuit to troubleshoot with a HV meter.
If you send me the brand and model tube I may
be able to tell you if
it's a soft sealed tube and other details.
Joe
At 04:38 PM 10/30/02 -0500, you wrote:
>I know this is a bit OT, becuase it's not really computer related, but the
>hardware is at least 23 years old, so that's my excuse for posting to the
>list...
>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. From the
>sound of the power supply it's either a loose connection (which I doubt
>after opening it up and taking a good look around) or there's a problem
>with the power supply.
>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?
>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.
>I'm just looking for general
guidelines.
>Thanks!
Pat
--
Purdue Universtiy ITAP/RCS
Information Technology at Purdue
Research Computing and Storage
http://www-rcd.cc.purdue.edu
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