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NDB7875 Winked out and I don't know why?

DistortedDesigns

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I bought a NDB7875 from DTR a couple of weeks ago. I am using it for laser engraving. I needed the extra power over my M140 to speed up some of my engravings. 7875 is the 3w everyone else seems to use because of it's relatively low divergence for a 3w / 9mm. Emblazer (laserblade) uses them as well as the guys over at picengrave.

I have done some preliminary photo engravings (Full Analog Engravings) trying to figure out speeds and was trying to get it aimed. I have maybe a half hour of run time. So the next day I haven't run it but about 3 or 4 minutes. I go to run some full power lines. The second it goes to full power it just winks out. No bright flash, no blue led, just black.... So I removed the 12mm module from the heat sink and tried to look at the laser module with my usb microscope. I don't have any way of removing the diode from the module or removing the cap off the diode. I didn't see any black or charred wires, or anything on the glass but without removing the cap it doesn't mean a whole lot. When I checked the diode with my meter it is measuring infinity.

I have double checked everything. I am using a flexmod p3 for a driver. I had it set for 2.3A Max. I am powering it with a 12v / 5A regulated power supply. I am using the z-bolt heat sink with a fan mounted to the top of it and blowing through through it and 3 other fans blowing down it inside of a wind tunnel. The Z-bolt is also mounted to a 1/4" piece of steel with cpu grease between the module and z-bolt as well as the z-bolt and piece of steel. You can see it here. It shouldn't be ESD because I wasn't touching the frame or anything else when it happened. It was also fairly humid.

Anyone got any ideas??
 



Pman

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Hang in there and I'm sure the help will come.
 
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Reattach it to the driver then power it up and measure voltage across diode. It could be the driver.
 

CDBEAM777

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I suspect the driver.

You can power the diode with a DC regulated Bench power supply.

With nothing connected...whatsoever...Set the power supply to 4.5 VDC ...then set the current to ZERO,

Now...connect the diode to the power supply...not a bad idea if you are wearing a static discharge strap,

Now....slowly increase the current on the power supply....likely around .5A...you should see some coherent light from the diode window,

As you increase the current....the power output should increase from the diode.

The NBD7875 should see a max. current of 2.4A

With your duty cycle....I would run max 2A....and...Keep it cool !!! which it sounds like you are doing.

If you get no output....diode is kaputz !! Shot !! Skunked ! DOA ! FAILED !!

Good luck !!

OH....and I would switch over to a driver from LSP or Lasertrac !!! IMNSHO:beer::beer:
 

Atomicrox

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Are you sure the driver can take 12V? Most of them are engineered to be powered by two Li-ion batts.
 

DistortedDesigns

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I know the driver (flexmod p3) is fine because I have already moved my m140 back over to it and have been burning images with it. The image I engraved last night took 3.5 hours to engrave. So that is out.

(The flexmod is made specifically for laser engraving and laser light shows. It is one of just 2 or 3 drivers that have full analog input as well as ttl. Fantastic driver especially for the money $35, if you can get one...)

The flexmod has 2 ESD protection circuits in it. Plus the odds of an ESD happening when I am not touching it or anything metal and it happens right when I turn it to full power.... So I don't think it was ESD. Also when it is ESD doesn't it still put out light but more just like an LED after an ESD? Mine is just BLACK nothing at all. There was no flash of extra brightness, it just went out like someone turned the power off.

I have so much heat sinking and moving air blowing through the heat sink that heat has never been an issue. I use a laser temp gauge to measure the temp of the 12mm copper housing. It doesn't get above 82 F after 4 hours of engraving (with the m140).

CDBEAM777 - I did all of that. The first thing I did was remove the diode from the circuit and add my dummy load to it to see if I could get the flexmod's protection circuit light to go out. It did go out and start working correctly. I checked the amperage settings to make sure which it was set for 2.3A below the recommended 2.4A max. I also left the 7 second power up intact on my flexmod for the extra protection during power up. When I do an ohm's check on the diode it reads infinity.
 

CDBEAM777

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Well....I missed the Ohm check note on your first post....Your LD is cooked, toast, fried.... FAILED !!

But why ????? Possibilities.....

1) Bad diode.....and bad luck to get it.
2) Something intermittent with the P3 driver circuit operations.
3) You had an intermittent connection to the diode...and that fried the diode. ( Cold solider joint)

I have had all three (3) conditions.

So....Buy a new 7875....and try again !

I prefer other drivers over the P3. No disrespect to Dr.Lava.....whom has moved this hobby more forward than I ever will....but....I just prefer other analogue drivers !!

If another 7875 goes winkie, winkie out....well...then ya know ...it is the driver !!

Do check, check and re-check the connections between the driver and LD.....I would even re do all that wiring !!!...maybe you have a cold solider joint on the wiring that connects the LD to the driver ???

Good Luck.

OH....Are u using a Lasorb to protect the diode ? Another well spent 5 bucks !!!

ANYONE else have a 7875 crap out like this ????
 
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DistortedDesigns

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I don't have a lasorb. The reason I didn't get one was it's size. I didn't think a lasorb would fit inside of the 12mm host. I thought I remember reading that they had to soldered directly to the legs of the diode for them to work (ie- you can't solder it to the diode wires after they exit the 12mm host and have it still work correctly). Lasorb's are also more expensive... like around $15 with shipping. Still worth it though.

I will check the power with an O-scope tomorrow to check for anything odd.

Also what other driver are you using with analog input. I only know of two others both are not from companies but just individuals selling on ebay. I would love to know of an alternative.
 
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Pangolin

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FYI: For anyone interested, there is an SMT LASORB solution. You can read more about it at the bottom of the data sheets section here:
LASORB datasheets - Lasorb

This was a relatively recent development, which was not available (or at least not known to be available) at the time DistortedDesigns made the post.

Bill
 




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