Bad Tube or PSU?

Discussions on optics for laser cutter/engravers

Bad Tube or PSU?

Postby timogiles » Mon Mar 18, 2013 12:19 pm

I'm having trouble figuring out if my tube has died or my PSU has died, hopefully someone with a similar experience can share their knowledge. I have a 40W 700mm CO2 tube and a standard 40W PSU. They originally came out of my DC-K40 laser and have about a year and a half of use on them.

This weekend I setup for a routine vector cutting job and when I hit "GO" the laser turned on for a split second and then the tube current dropped to zero. I stopped the machine and checked all my connections, but everything seems fine. I'm not getting any strange smells or sounds and upon opening up the power supply I didn't find anything that looks visually damaged. From reading through the forum it looks like most people experience a period of reduced power output from a tube before it dies, but my tube was running fine a few days prior. All the lights on the PSU are operating as normal. I checked the internal fuse and it is fine.

Has anyone had a similar experience?

Is there a good way to test my PSU?

When a tube "dies" does current still flow through it? There is no current flowing through my tube right now and no plasma.
WildCircuits.com
timogiles
 
Posts: 27
Joined: Wed May 19, 2010 11:41 am
Location: Rochester, NY

Re: Bad Tube or PSU?

Postby bdring » Mon Mar 18, 2013 2:55 pm

I have had 2 power supplies go. I have replaced 1 tube after it lost power. I have never had a tube just go dead.
Bart
"If you didn't build it, you will never own it."
bdring
Site Admin
 
Posts: 2966
Joined: Sun Nov 22, 2009 7:33 pm
Location: Chicago, IL, USA

Re: Bad Tube or PSU?

Postby timogiles » Mon Mar 18, 2013 3:44 pm

Interesting. I have been thinking that it is likely the power supply, but it's hard to know for sure. What symptoms did your power supplies give when they needed to be replaced? did they just stop working?
WildCircuits.com
timogiles
 
Posts: 27
Joined: Wed May 19, 2010 11:41 am
Location: Rochester, NY

Re: Bad Tube or PSU?

Postby timogiles » Mon Mar 18, 2013 9:06 pm

Anyone else care to chime in?
WildCircuits.com
timogiles
 
Posts: 27
Joined: Wed May 19, 2010 11:41 am
Location: Rochester, NY

Re: Bad Tube or PSU?

Postby bdring » Mon Mar 18, 2013 9:19 pm

I though I heard a little pop when mine went, but it was not load enough to make me think anything broke. There was no smoke or smell either.

I don't think anyone is chiming in because it is hard to tell whet happened. There is no safe way to test for the average mortal user.
Bart
"If you didn't build it, you will never own it."
bdring
Site Admin
 
Posts: 2966
Joined: Sun Nov 22, 2009 7:33 pm
Location: Chicago, IL, USA

Re: Bad Tube or PSU?

Postby macona » Tue Mar 19, 2013 7:57 am

I had a 80 watt PSU die once. Just stopped working. Found a blown mosfet inside, it was replaced under warranty so I didnt do anything more.

Tubes should not just stop working unless there was a sudden breach and it came up to air. But since you saw it flicker the chances are that it is the power supply.
macona
 
Posts: 363
Joined: Tue Aug 17, 2010 10:30 pm

Re: Bad Tube or PSU?

Postby twehr » Tue Mar 19, 2013 11:54 am

I am curious... Have you checked to ensure that the power supply is actually receiving a signal to fire the laser? (Alternatively, have you tested by pressing the test button on the power supply?)

If that does not lead you to it, I would suspect the PS. The "pop" is probably the most significant sign. If you open the PS, you will likely find that a good portion of it is has been filled with a plastic-like substance. If an electronic element inside that went out, you might not see or smell anything.

I had one PS go out (with a pop). The pop was a spark from the tube connection to ground (trough the insulating tape I had on it). Tube, itself, was fine - just fried the PS.
tim
--
"The answer is usually easy and obvious once you know what it is." tw

DIYLaser Blog
SemiHomemadeTools.com
twehr
 
Posts: 439
Joined: Mon May 24, 2010 4:49 pm

Re: Bad Tube or PSU?

Postby timogiles » Tue Mar 19, 2013 10:52 pm

macona wrote:I had a 80 watt PSU die once. Just stopped working. Found a blown mosfet inside, it was replaced under warranty so I didnt do anything more.

Tubes should not just stop working unless there was a sudden breach and it came up to air. But since you saw it flicker the chances are that it is the power supply.


The FETs in my supply don't show any physical damage, and I'm well past my warranty. I generally waste no time voiding those. :D

twehr wrote:I am curious... Have you checked to ensure that the power supply is actually receiving a signal to fire the laser? (Alternatively, have you tested by pressing the test button on the power supply?)


Yes and Yes. Those were the first and seconds things I checked.


So here is the verdict: PSU

A friend of mine at work used to have a TV repair business and had a high voltage probe. He let me borrow it. It's a BK Precision HV-40.
P1030923.JPG
BK Precision HV-40

Touching the tip of the HV probe on the tube connection with the red wire and the ground clip connected to the laser PSU chassis I could only barely see any movement of the needle. That ought to equate to something less than 1kV. I think it's pretty safe to say that the PSU is bad. I've got a new one on order.

Here are some pictures of the internals:
P1030917.JPG

P1030918.JPG

P1030919.JPG

P1030920.JPG

P1030922.JPG


Thanks everyone for adding your 2 cents. I'll update again once the new supply comes in and my laser is back to working.
WildCircuits.com
timogiles
 
Posts: 27
Joined: Wed May 19, 2010 11:41 am
Location: Rochester, NY

Re: Bad Tube or PSU?

Postby AVRC » Tue Mar 19, 2013 11:13 pm

Maybe it's the photo, but the transistor on the right in your second picture looks messed up to me.
Look closely at its lower left corner.
AVRC
 
Posts: 20
Joined: Fri Mar 02, 2012 3:34 pm

Re: Bad Tube or PSU?

Postby timogiles » Wed Mar 20, 2013 3:22 am

I think you are just seeing a slight build up of dust. Here is another shot of it. The yellowish mark on the front of the transistor is a reflection of the yellow coloring on the frame of the transformer between the two FETs.

P1030925.JPG
WildCircuits.com
timogiles
 
Posts: 27
Joined: Wed May 19, 2010 11:41 am
Location: Rochester, NY

Next

Return to Optics and Lasers

Who is online

Users browsing this forum: No registered users and 6 guests

cron