Laser PSU Noise

Electronics related to CNC

Laser PSU Noise

Postby TLHarrell » Tue Dec 20, 2011 2:25 am

I think it's the laser power supply. Anyway, I'm having what seems to be reduced and intermittent laser power. What used to slice through 1/8" MDF is barely making it in two passes, and some parts aren't even cutting through.

I've been running some test cuts, 1" square at 15ma, 50% speed. First pass sounds about normal. Second pass starts sounding louder. Third pass, the whine gets intermittent. It keeps getting louder and nastier sounding from there.

A couple runs, I did a two pass, and at the end of the cycle the laser stayed on. Had to e-stop it.

Is this a sign of my power supply going on the fritz? Anybody want a sound recording emailed to them to check it out for me? I've got a couple orders to do, and I'm sitting here unsure if I'm going to cause further damage if I continue.
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Re: Laser PSU Noise

Postby lasersafe1 » Tue Dec 20, 2011 7:59 pm

It sounds like the supply is the problem. Assume tube water flow is good? I would temporarilly take the supply to manual control mode with a pot to verify it is the supply and not any attached controls.
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Re: Laser PSU Noise

Postby TLHarrell » Wed Dec 21, 2011 3:35 am

Water flow is good, and since it's been consistently below 65F during the day, and in the low 30's at night, the water is nice and chilly.

I was thinking it would be a good idea to try swapping the pot back on and see if the digital control is being funky. If it is the power supply going bad, is there any issue with continuing to run the laser while waiting for a new one to arrive? I'm wondering what a PSU's usual mode of failure is. Does it just give up and go cry in the corner, or does it let out magic blue smoke, flames, and throw lightning bolts at my driver board?
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Re: Laser PSU Noise

Postby TLHarrell » Wed Dec 21, 2011 4:57 am

Laser power supply is completely silent when using test fire buttons. The sound does seem to be coming from the PSU, but I'm thinking the controller card (Retina) might be the issue at this point. I am having a completely repeatable issue with the laser not turning off at the end of the run on my 1" square test pattern when it is run in two passes. One pass it works as normal. When the laser remains on, the e-stop and laser on/off buttons will stop it, but upon clearing any of those it resumes firing. Pulling the USB (which is power to the Retina card) shuts off the laser. I've also started having RetinaEngrave locking up. Sounds to me like a hardware issue. Hopefully support will clear this up. I'm shut down until I can get this resolved.

...at least I don't have to buy a new PSU... yet.
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Re: Laser PSU Noise

Postby iGull » Wed Dec 21, 2011 11:39 am

Ensure all your system power supplies are ok for voltage and ripple (you'll need a 'scope for that). Cheap chinese PSU's normally don't include high quality output capacitors (or high quality anything for that matter LOL :D ) and have a tendency to go open circuit causing massive amounts of ripple. If you don't have a 'scope, see if you can swap out your power supplies with new ones temporarily.

Dodgy PSU's are the most common fault in any system and can cause extremely oddball faults that seem attributable to something else.

Cheers

Neil
EMOs are a sign of weakness ...
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Re: Laser PSU Noise

Postby TLHarrell » Wed Dec 21, 2011 10:05 pm

I'm going to see if I can beg/borrow/steal a scope. I'm not an expert with electronics, merely light hobby level. Any chance you can walk me through some testing methods to confirm/deny the power supply issue? I've never used a scope, and I'm not sure what I'd actually be looking for. (That, and I'd hate to blow up a friend's scope by hooking it up wrong.) If I'm going to build my own laser, I better get started learning some of this stuff.
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Re: Laser PSU Noise

Postby iGull » Thu Dec 22, 2011 3:09 pm

TLHarrell wrote:Any chance you can walk me through some testing methods to confirm/deny the power supply issue? I've never used a scope, and I'm not sure what I'd actually be looking for. (That, and I'd hate to blow up a friend's scope by hooking it up wrong.)


Hi

(I couldn't get your name from your sig :) )

There would be no problem walking you through it if I was sitting on your shoulder - doing it over the net is a different matter altogether :D All scopes are not equal, controls are different and some of the more up to date units require a first degree in astro physics to drive them :D Also, as you say, you wouldn't want to blow up his scope (unlikely though that is :) ).

Here's what I would suggest, if you can get a scope from a friend, bring him or her along to drive it.
First check each PSU for the correct voltage with a DVM (on load - make sure everything is on) - the voltage should be within about 0.2-0.3V of the nominal PSU voltage. If any are well off the mark, that may be your problem.
Hook up your scope to each PSU rail in turn - scope ground to system PSU ground and the probe tip to each positive rail in turn. Scope should be set to about 10mV/cm AC coupled - set trigger to auto for now - again make sure everything is on and loaded up. There may be some random system 'noise' which may involve fairly high spikes (in a perfect system, they wouldn't be there, but nothing's perfect). On 'old' analogue supplies, we would be looking for mains ripple (50Hz europe - 60Hz US) - but most modern el cheapo chinese PSUs are switch mode, so it will be a high frequency ripple instead - let's say about 20KHz for now. If this ripple is more than about 300 - 500mV, you may have a problem.

If you can't get a scope or a good set of replacement PSU's, you could temporarily swap out the supplies with batteries - don't use ordinary alkalines, I would suggest NiCd or NiMh - a high current model a/c Rx pack of about 2200mAH at 4.8V will hold the system 5V up for a while - a 12V Tx pack of the same will do your 12V - ditto a pair of Tx packs in series for the 24V - or even combinations of Rx packs. I don't know what your system consists of in the way of PSUs - I have 24V for the steppers and a separate isolated 12V with 5V and 3.3V derived from that . The good thing about using batteries is that they are noiseless and can show up other issues - odd things like 'artefacts' being printed - zig zags, rough edges and the like - all attributable to bad PSUs.

It's conceivable of course that the controller IS bad :D

Hope this helps.

Cheers

Neil
EMOs are a sign of weakness ...
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Re: Laser PSU Noise

Postby TLHarrell » Thu Dec 22, 2011 6:36 pm

I got a negative on the beg/borrow/steal. Looking to add a DSO Nano to my kit. Not too bad on EBay for +/- $75 delivered.

I'll have to make do with my DVM for now and play around with the PSU. It seems that's the culprit, but I'd like to isolate it as well as I can before dropping the coin for a new one. I hope I can get my machine up and running soon. I need to start gearing up for Valentine's Day stuff.
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Re: Laser PSU Noise

Postby mikegrundvig » Fri Dec 23, 2011 4:50 am

I've used this before as an O-scope quite a while ago:
http://www.societyofrobots.com/sor_scope.shtml

Basically, it uses the Axon II microcontroller board and provides a pretty solid scope for free. It will cost a ~$110 all told but you get a really killer microcontroller (designed very strongly for robots and automation) along with a reasonably capable scope.

-Mike
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