Help Pls! Prev Burns to 12% higher no burn, New Flyback, ammeter fit, just pink glow, no power/burn

Hi please could somebody advise a newbie?
I bought a 2nd hand K40, they said not used much.
It test fired but only burned paper at 12%, higher powers no burning.

Changed flyback, added ammeter.
Now get pink glow on test fire but will not burn or scorch paper throughout the power range below.

% mA
5% 0.5
10 2.7
15 2.7
20 5.0
25 7.1
30 8.3
35 9.5
40 10.3
45 11.3
50 12.3
55 13.8
60 14.8
65 16.0
70 17.5
75 18.6
80 20.0
85 21.0
90 22.5
95 23.7
100 24.9

I am away from 10/8/20 til 18/8/20 so sorry cant respond in mean time.

Many thanks in advance if anyone could help.

Original Flyback was:

replacement was:

1 pin type

Your power curve looks pretty close to normal:

Have you done an optical alignment, inspected all the mirrors and the objective lense?
Do you have the bed at the right focal length?

Hi Don, many thanks for responding. I am holding paper directly in front of the end of the laser tube so there is definitely not much light coming out.

What colour is the plasma in the laser tube? It should be pink/purple. If it is white/grey, your tube is no good and needs replacing.

Hi, thanks.
It is pink slightly purple.

Do you see any cracks in the tube?
What coolant are you using?
Post picture of the dot burned on paper at the output of the tube.

There is no dot on the paper, no mark whatsoever.
I’ve tried cleaning the output laser mirror, seems clean enough.
I am using deionised water.
There are no signs of any cracks.

When I attached the HV lead from the flyback I used one of the connectors from inside a small terminal strip as below, (filed down screw to fit inside silicone tube and then siliconed).
When I tightened the screw I am not sure if I heard a faint crunch. I thought it would probably be all right as it may just be very thin layer of glass that tapers down to nothing around the HV terminal.
Absolutely no signs of cracks around the HV terminal as far as i can see without taking the silicone off.

If there were any leaks surely the tube would not make the pink slightly violet glow in the tube?


Very strange, I wonder if there is something wrong with the output mirror.
Post picture of the tube firing if you can.

I have had the same issue recently. Mine was working fine then the next job - trying to cut a stencil from card stock - failed. I tried 6 passes at 10mm/second and couldn’t burn through. I though something happened to my mirrors so I put paper on them to check alignment and hit the test fire button. There wasn’t even a mark on the paper on the first mirror. The laser tube was glowing pink when fired. Eventually, I just pressed the test fire button and held it. After a couple seconds a large 1/4" double mark (two half moon shaped marks) started to burn into the paper. I assumed the tube was going bad so I ordered another one. I believe somebody recently had a similar post on here somewhere about it, but for the life of me I could not find it.

Like this?:

When lasers go bad they sometimes change modes.

@donkjr I’m trying to figure out where in the Getting Started category to put information on TEM01 — it’s certainly come up recently but isn’t in the intro docs. Ideas?

Please find photos one with and one without flash.
Absolutely no marks on the paper.

@mcdanlj I would say put tube modes in an area that talks about indications of tube failure.

As a stab in the dark try bypassing the current meter and directly ground the cathode.

Just tried that, no difference unfortunately. Will just order a tube now via aliexpress.
Thank yo for your efforts.

Thanks to everyone for your help and efforts. If I find out what happened I will post on here.

Please do! Every time someone shares what worked for them it helps the next person and pays it forward! :slight_smile: Best of luck with the replacement!

Like the one on the right (TEM10). Thanks. The original tubes must be crap because I have well under 100 hours on it. I doubt if I had 50 hours on it.