DHOM 532nm TEC setup appears to be totally Kaput!

[catalanjo]

Help needed desperately !

I have a problem with a recently purchased DHOM 532nm (model DHL-100A PSU, and model DHL-W532-1000mw head).

Power starts off nice and high and well over spec when first switched on but degenerates to less than half a watt within minutes.
If I switch off for a few minutes then switch back on the symptoms repeat themselves.

I can not detect any heating what so ever on the base of the head module so I assume that the peltier/s is/are not operating correctly.

Does anyone have a schematic for this laser since I need to know whether the problem is the temp sensor in the head, the peltier itself or the peltier driver.

I am loathe to take the head apart as dirt could possibly get in since I do not have a class A clean room or anything remotely similar so I would prefer to diagnose the fault from the PSU end of things for the time being.

I feel I have probably been sold a pup since I can not imagine how this type of fault could have possibly have developed during transport.

Does anyone have any thoughts on this ???.

Has anyone ever heard of a thermistor getting "bumped-off" or a TEC circuit giving up the ghost when obviously not powered up ?

The laser was switched on only ONCE for less than a minute using a 4.5volt battery as modulation input to check that it was lasing on arrival and then immediately replaced into its packaging before I got to test it properly with my Ophir power meter five weeks later.

I have already checked for any apparently loose wires and found none in either plug or socket on the PSU.

There is a fully populated 8pin socket on the PSU and a plug on the cable connecting the PSU to the head (which is hard wired into the head through sealed case holes). Since inside the PSU these eight wires split into four two pin connectors on the main controller board I assume the following in absence of further info:

Two of these are the fan supply the other six are probably 2 x pump input, 2 x peltier drive and 2x temp feedback suggesting that there might be only one peltier for the entire optics train!
Although ideally I would expect at least two peltiers, (one for pump and the other for the frequency doubler and stretcher crystals) and two temp feedback devices.

However despite the four way split in the PSU it is conceivable that there are common rails which would allow for another peltier drive and another temp feedback signal especially if the fan supply is shared with the pump input (very dubious but still possible). The internal PSU wiring design and the wire thicknesses (four thick and four thin however make all this somewhat unlikely).

Also since this laser is clearly of Chinese origin the design criteria is more likely to favour price and carefully selected crystals over thermal stability and linear modulation characteristics.

I am somewhat up shit creek without a paddle here !

Even the wiring diagram (or just the pin out) for the head to PSU connection would be a great help since this would enable me to monitor the peltier drive voltage/current and the temp feedback from the head so as to help diagnose the exact nature of the problem.

Does anyone know if DHOM lasers frequently suffer this type of fault ??

Who has repaired/stripped/rebuilt one of these babies?

Any info will be gratefully received either as a post or a PM.

Thanks!

Cheers

[laserdj]

I Have a DHOM 800mw 532 that starts fine then begins to fade... then some times it kicks back full power after a while, sometimes not. Seems we have the same problem, not a clue what it is...

[norty303]

If they were recently purchased, why don't you warranty return them?

I had a Laserwave green that was doing similar things, quite heat sensitive. Rob had a look and found the SHG wasn't well coupled to the cooling so it was over sensitive. He sorted it and its calmed right down now.


Also, have you tried contacting Marc or Shawn (iirc) to see if they can help with schematics, as they are the distributors (I think)

[300EVIL]

I'm not saying this will solve your problem but try warming the head with a hair dryer to about 85F while it's running and monitor output power. KTP does not like to lase when it's too cold. If your power output further degrades, its most likely a TEC fault as you pointed out.

[catalanjo]

Hi people, many thanks for the quick responses they help keep my spirits high, solidarity is a great feeling. It feels like I am getting somewhere albeit one minute step at a time.

Still searching for specific DHOM info !

@Evil
Thanks for suggestion Adam a bit rough but very simple and effective, and this, as you point out would at least confirm beyond doubt that it is a definitely a TEC problem not a stray ant or some weird "laser bug " LOL crawling around the optical cavity.

@Norty
No warranty I am afraid since I purchased it second hand albeit with excellent seller references from a PL member.
With regard to SHG thermal coupling, I find it difficult (though not totally impossible) to believe that transportation, in a well packed box, could influence this. This possibility would tend to confirm that the seller was aware of the problem and kept mum about it and I am trying to avoid this conclusion as much as possible until such time as a precise diagnostic becomes available.

Forgive my higorence .... but what does (iirc) mean exactly ?

Pointers to Marc (presumably = CT and Shaun = in Canada?) will probably be useful.
Thanks a bunch.
Rob would be a great solution but I am at present with the laser in Spain not UK, and also he is more LW than DHOM I think.

@laserdj
I think we may have similar problems, but by no means identical ones. Your problem sounds intermittent and unpredictable, mine in contrast occurs like clockwork every time. The only thing they have in common, is probably that both are cooling issues.
Once I have the info I need, I will endeavor to try and help you with your situation which sounds very embarrassing if you are doing gigs. Please do NOT sell this laser of yours without advising any prospective buyer of the problem,(for some poeple it is a small problem, for others it's gigantic and would be most dishonest although probably very easy to achieve).

Cheers

[buffo]

Hey Lari;

First: iirc = if I remember correctly (internet shorthand)

Second: I can vouch for the fact that the laser did not have this problem when I had a chance to test it (which was about 7-8 weeks before you bought it). I ran that laser for several hours at full power without any problems. (I also ran it for a couple hours under normal modulation, to be sure it didn't jellybean.)

That doesn't mean that a problem didn't develop during shipping, of course. I'm not doubting your report that it's got problems now. But I had originally intended to purchase it myself, which is why I tested it so thoroughly. I can promise you that Jeff did not knowingly sell you a defective laser. For one, he doesn't operate like that, and besides, I *know* that laser was working as advertized when I had it. Jeff didn't do anything more with it besides power it on shortly to take a couple pictures before he listed it here on PL.

Anyway, I just had a thought... That laser is probably still under warranty even though it was transferred to you. I know I was able to claim the warranty on my Lasever unit even though I wasn't the original buyer.

So before you open it up (possibly voiding the warranty), maybe you might be better off sending it back to China to get it repaired professionally... I think it's worth checking into anyway.

Have you contacted Jeff about it yet? (Do you want me to call him?)

Adam

[catalanjo]

Hey Lari;
Have you contacted Jeff about it yet? (Do you want me to call him?)
Adam

Hi Adam,
I had hoped to be a bit more discrete about this until I have a firm diagnosis.
No I haven't contacted him as yet since I prefer to have a recorded printout of the power output before doing so.
I am busy mounting a test rig right now as per my PM.
I will PM you as soon as I have results.
If there is any chance of a warranty YES please contact him for details.
I have only looked at the PSU plug so far so no seals broken until authorised to do so by Shaun or Marc.
Who was this laser originally purchased from ?
Thanks for the reassurance.

@laserdj
Have you talked to Shaun about your DHOM problem ?


Cheers

[catalanjo]

Hey Adam,
Regarding the fan noise :
http://www.photonlexicon.com/forums/...ght=ultralaser

Looks like my girlfriends little brother was not the only person to remark on this !

So I assume it to be normal for this beasty!

Cheers

[kecked]

I have 500mw and there is knee just like every dpss green out there. I run under the knee to avoid it and it is linear as a ruler. Mine works quite well. Contact Shawn and he will fix you up. ultralasers@gmail.com This is direct to Shawn.

[catalanjo]

I have 500mw and there is knee just like every dpss green out there. I run under the knee to avoid it and it is linear as a ruler. Mine works quite well. Contact Shawn and he will fix you up. ultralasers@gmail.com This is direct to Shawn.

Thanks for direct Shaun link (email I had for him was different and quite ancient) !

Unless I misunderstand you completely the "knee" in my case would be a maximum power that did not require TEC which in my case (since TEC clearly isn't functioning ) would be about 300mw so not very useful really!

But thanks for advice, I will "explore" the knee I think you refer to once I have the TEC sorted and post results on this thread.

Cheers

[kecked]

What I mean is that as you increase power there is a point where the laser suddenly drops in power and then recovers a little bit later on. It is a small area where the laser losses power. There is a device made by the same greek company that makes eyemagic scanners that can correct for this. It is $800.00 so I never bothered. I just use a laser big enough that I have the power I want below the lasers knee. For me 500mw is a lot of green. I only have 1watt blue and 800mw red so I use maybe 200mw-300mw of green max. In my living room that is a lot of power. Heck I remember when I only had 125mw total from my argon and 35mw from my hene on a pcaom. So no complaints from me. I must say gas lasers and a pcaom made for a lot better beam quality. I still miss perfectly aligned colors and no color tails of any kind. You could also go for an AOM and not worry about it at all.

[blrock]

If you recently purchased it as you say I suggest sending it back. One of my first 800mW lasers (from Lambdapro) had a similar problem. I send it back and the report I received stated that the TEC came loose during shipment. They repaired it and covered shipping.


I have a DHOM which gives a very stable 1700mW. Seems to be a nicly build laser. These mishaps happen(especially with dpss technology). I reckon sending it back and not void your warrenty by opening it.

[catalanjo]

What I mean is that as you increase power there is a point where the laser suddenly drops in power and then recovers a little bit later on. It is a small area where the laser losses power. There is a device made by the same greek company that makes eyemagic scanners that can correct for this. It is $800.00 so I never bothered.

OK so we are talking about modulation linearity. Not my problem yet unfortunately..... but if it was, I think I would make something myself, rather than dish out 800$.

Thanks for the info though!

@blrock = Warranty still uncertain since laser was purchased second hand, and any shipment back to China would have to run the Spanish customs gauntlet yet again ......which took almost a month the first time round since it arrived just before Semana Santa (Easter) !

Prefer to fix it myself if possible. since I also prefer to know all the details about how my lasers work.

Cheers

[catalanjo]

It would appear that this laser IS still under warranty!

So with a bit of luck and some help from Marc and Shawn I might be able to get this sorted soon.

Marc has had strange DPSS laser failures caused by slight knocks let alone international shipping so there is a lot more to this situation then meets the eye.

It might be down to DHOM using a single TEC for both pump and SHG.

Full power plot and temperature data now logged but I don't know how to post it here. If anyone is interested just post instructions as to how I post the excel files concerned.

I will update the thread as things move forward.

Cheers

[sugeek]

Full power plot and temperature data now logged but I don't know how to post it here. If anyone is interested just post instructions as to how I post the excel files concerned.

I will update the thread as things move forward.

Cheers

Two ways... 1) Take a screen shot of it and post the image file. 2) Change the excel file extension from .xls (or whatever form it is) to .txt or .jpg to trick the file attachment filter to let you upload it.

-Adam

[catalanjo]

Two ways... 1) Take a screen shot of it and post the image file. 2) Change the excel file extension from .xls (or whatever form it is) to .txt or .jpg to trick the file attachment filter to let you upload it.

-Adam

Thanks mate I will try to do this tonight when I have more time.


Cheers

[catalanjo]

Update !
Seller has kindly offered to organise a "return under warranty" but I am really worried about what happens in Customs when the laser comes back from China to Spain.

Anyone got any ideas concerning this problem ?

Data plots of power output will have to wait till tomorrow since I am on a friends computer right now!

Cheers

[catalanjo]

Update!

Seller has offered full refund if I want to return the laser which is incredibly generous since he is fully aware that it is unusable.
Cheers Jeff

However since I do not think he is to blame in any way I do not want to dump the problem back in his lap!

I still have no further info on the umbilical plug wiring so clear diagnostic of exact fault is not available as yet.
Any info regarding this will be gratefully accepted.

Tried uploading jpeg using the "File Upload Manager" with no success. Maybe due to Win98 Op sys.

Will try tomorrow using XP

Cheers

[allthatwhichis]

Have you ordered a laser from China before? A lab module should have no problem as they usually don't in the US.

[catalanjo]

Yes but shipments always passed under the radar due to low value.... in this case I am terrified of Spanish Customs hassles on return shipment since they will probably declare full value for insurance purposes.

That is why I would prefer to check that this is absolutely necessary before shipping laser back to China.

If it turns out to be an electronics issue in the PSU then it may be better to fix it here, but for that I need the info about what to measure and where to measure it.

Just occurred to me that I am running at 220VAC whereas in USA it was running at 110vac.
According to label on PSU it should accept from 100 to 250VAC and there is no sign of a commuter inside so next test will be using 110 as soon as I lay my hands on a suitable trafo.

Cheers

[catalanjo]

Update:

Managed to insert file using XP .....so here it is


DHOMtest1.jpg

I also have more logs which I will post later using different ambient temperatures with the help of an air conditioner. This is just the clearest one I made the first day once I had the test rig set up.

However my latest idea to try a 110vac input will have to wait since all my trafos are a hundred kilometers away in Barcelona and I am up to my ears in work in a village up the coast on the Costa Brava right now.

Cheers

[300EVIL]

Update:

Managed to insert file using XP .....so here it is


DHOMtest1.jpg

That looks pretty normal to me.... Unless it's just completely shutting off on it's own at the end of the graph there....

Another question would be, is the power supply providing enough current to the laser driver? It could be that you are reaching the maximum rated current output of the power supply as the TEC's require more as the head warms up.

[allthatwhichis]

I agree that looks normal to me also; it is a 1 watt laser that produces 2 watts for a few seconds then drops to around 1.5 watts... I assume you powered it down after 2 minutes? I would be worried if it dropped to a half watt after the 2 watt jump; 1.5 watts from a 1 watt laser is more than acceptable. What happens after 10 minutes?

[catalanjo]

That looks pretty normal to me.... Unless it's just completely shutting off on it's own at the end of the graph there....

Another question would be, is the power supply providing enough current to the laser driver? It could be that you are reaching the maximum rated current output of the power supply as the TEC's require more as the head warms up.

Yup laser is shutting down all by itself (no warning led on this occasion since mod input voltage was 4.5vdc (battery), when I went up to 4.9vdc (bench supply confirmed with Fluke) the warning "Alarm" led came on within one minute so all other logged tests were done at 4.5v. Most of these tests showed the laser settling to an output of about 500mw for extended periods (ten minutes or more) before shutting down completely.


current to laser driver = aha! that is the question !

but I still do not know the pin outs of the umbilical between the PSU and the laser so I don't know which points to monitor. No info has arrived as yet from either Shaun or Marc and I can not proceed easily and safely without this info since tracing the wiring would mean opening the head (voiding possible warranty) ....... unless you can suggest some more ideas to try! (non destructive naturally)

I suppose these DHOM PSUs are fairly recent on the market so no one has taken them apart yet.
Thanks for your interest Adam. All this would be a piece of cake if someone could give me a guided tour of the DHOM PSU in question.
My self confidence in electronics doesn't stretch to voiding a warranty by sticking my foot in it whilst measuring voltages and currents, although reason tells me this shouldn't affect anything at all due to the extremely high impedance of the meter when measuring voltages and the extremely low one when measuring current.
My warranty paranoia stops me short of just clipping the test leads on to all the combinations available.
I do also have a non contact clamp meter for DC current but it is not very sensitive and the PSU internal leads aren't long enough to wrap a few turns round the its jaws.

Do you think my Fluke could cause any damage in its DC voltage setting if I pick the wrong leads ?

All suggestions gratefully accepted... curiosity is gradually replacing desperation fortunately !

One of the things which pisses me off about warranty returns is that you never get to find out what was going on and what went wrong (let alone why), they just fix it (hopefully) and send it back with no explanation whatsoever.

I did try your preheating idea and the laser turns off much faster if I go up to local ambient temp of 35C and much slower if I go down to 18C This would tend to confirm the failing TEC diagnostic.

I will post further test results at different ambient temps once I get back to XP (in linux right now) and I can't seem to upload files to PL. (They all show much the same story however).

Strangely for a DPSS, even when at fairly chilly ambient temp the immediate startup power output is pretty high.

Cheers

[300EVIL]

Okay, Is the power supply and laser driver located in one enclosure? If it's a lab style, it would plug into the wall. Or is there a separate power supply and driver like in this pic?