Opinions/options re: power loss on Lasever blue DPSS

[buffo]

Hey folks;

I've got a Lasever DPSS blue laser that is about 2 months old. It used to make roughly 110 mw of 473 nm. The driver board normally draws nearly 5 amps of power at 5 volts DC from it's power supply. There is a heat sink and fan mounted on the driver board, and another heat sink and fan mounted on the head itself. Normally the head would get warm to the touch during operation, and so would the driver board. Not hot, but warm. (For those of you that are wondering, this is one of the lasers that I bought from Fred when I bought his optical table.)

Now that everything is installed and running on my new optical table, I've discovered that the blue laser is only making 40 mw, which is less than half of it's rated power. Also, the head stays cool all the time, and so does the power supply. I checked the current draw, and it's only drawing 3.7 amps. Voltage supplied to the driver board is still constant at 5 volts. Apart from the low power, the beam quality is fine, and the analog blanking circuit is working just fine as well.

I've done several tests to confirm that the problem is with the laser/driver combination and not a grounding or blanking signal problem, including:

1) connecting the blanking leads (+5 and gnd) to the same power input terminals that the driver board uses to ensure that the blanking circuit was seeing a full 5 volts.
2) ensuring that the head and driver board are grounded together. They are mounted on the same aluminum plate, but I actually ran a jumper from the case on the driver to the head housing to be sure.
3) connecting a separate, filtered, bench power supply with precise voltage control to the driver board to rule out possible problems with the existing AC power supply.
4) checking all connections twice to be sure everything is tight.

I also disconnected the blanking leads from the blue laser to the ILDA connector for all the above tests to rule out any possible interference from the common ground line for the other laser's blanking signals on the connector. In fact, the other lasers weren't even powered up for these tests.

I can't think of anything else to try. From what I can see, the laser diode just isn't drawing as much current as it used to, which is why the laser output is lower. (This would also explain the lower temperature on the laser head.)

Now, I suppose it could also be a problem with the TEC in the head, since it might be responsible for roughly an amp's worth of current draw, but would that cause the power output to drop by more than half? (I dunno.?.)

The driver board has two green LED's that are supposed to light up whenever the laser is on, and both those LED's are on as normal. The driver is supposed to have a red LED that will light up when the head overheats, but that LED is not lit up, and the head is cool, so I'm fairly certain that HEAT isn't a problem. (Is it possible for the head to be too cold though?)

Fred and I have discussed this problem at length, and we can't figure out what is wrong... Anyone else have any ideas/things to check before we send it back to China?

Adam

[DZ]

Hmm, interesting issue. Just a few thoughts I had regarding this, Perhaps you can check the blanking cables in the driver, make sure they are still in good shape. I noticed on mine that they are rather cheap cables and I had suspected that too much flexing of them could cause an issue, but in this case it may have developed a resistance. Perhaps, flexing and lightly pulling on the cable while it is attached to the terminal lugs could help to see if this is an issue. Also, if your brave enough, you could always adjust the diode current pot one way, about an 1/8th CCW, then 1/4 turn CW, then back to center 1/8th CCW. Just to clear off any potential carbon build up on the contacts in the POT. And if you are very brave, you could always ramp up the diode current and see what happens.

David

[buffo]

David;

Thanks for the input! I am *not* brave by any means, though I see what you're getting at. I might give the current adjust pot a tweak with the power removed, so long as I can be certain I'll get it right back where it was before I power it up again. I don't want to try to increase the diode current beyond the norm though, because I'm afraid of blowing the diode. (The unit is still under warranty.)

I agree that the blanking wires looked a bit flimsy. I'll have a look and see if they've worked loose from the point where they're attached.

Adam

[The_Doctor]

I think that TEC idea is worth exploring. Do you see any unusual mode hops or obvious erratic behaviour during warmup, that you're not used to seeing? If so, it might mean the pump diode's TEC isn't being controlled or powered correctly due to a fault.

Another possibility is that there might be more than one stable temperature for the TEC control. There shouldn't be, but I've seen it happen in a Lamdapro laser I have here, a 200 mW unit that puts out less but in a very fine beam worth keeping it for. This thing would poorly regulate temperature, if it got warm, the sensor assumed it had to pump harder to cool it, which made it get warmer, until at some point it balanced and thought it was happy. It shouldn't be though, it was better on a solid heatsink which prevented the case temperature rising so fast, which allowed the TEC controller to reach equilibrium at a cooler hot side temperature. There might have been several points where it might have assumed it was correctly set. I never found the right one, I ended up setting it to the lowest TEC drive that got a decent output. I couldn't figure out the circuit because LambdaPro grind all the chip numbers off.

That might not help you, but you changed the heatsinking conditions, so it's worth considering. I agree that the TEC is the single most likely thing to account for that kind of change in case temperature and power draw, and this is one mechanism that could account for it. While a good TEC system should keep the cold side temperature constant regardless of hot side temp (within reasonable bounds), it actually reads the sensor not the real temperature, which might differ, especially if the hot side temperature moves through a large change.

[allthatwhichis]

Damn man you aren't having a lucky time are you? and I got nothin... Just wanted to comment. Good luck!

[buffo]

Do you see any unusual mode hops or obvious erratic behaviour during warmup, that you're not used to seeing?

Hi Doc;

No, I don't. The beam is TEM00 and stable throughout the warmup period. No mode hopping, no satellite beams. The only thing that changes is the power level and the current draw.

When I first power it on, it's making about 20 mw and drawing around 2.6 amps. But the current draw quickly rises above 3 amps during the first 20 seconds or so, and the power output rises to nearly 30 mw. Then the current draw slowly creeps up to between 3.6 and 3.7 amps over the next 2 minutes, and the power rises to a peak of 40 mw. From that point on, output power and current draw are unchanged.

Another possibility is that there might be more than one stable temperature for the TEC control.

Yeah, I see where you're going with this, but for there to be a second, stable plateau for temperature control that also coincided with a lower current draw, it would mean that the head would have to be a lot hotter than normal. (TEC working less hard = less current draw but also less heat removed so temp goes up.) But in my case the head is actually a bit cooler than normal, which doesn't make a lot of sense to me... (Unless the diode is just not drawing the same current as before and thus is running cooler...)

Also, I really didn't change the heatsinking conditions. The laser is mounted on the same base plate with the same heat sink and fan that Fred used in his projector. (The laser is mounted to a plate, which is then suspended above another plate.) The entire table is now mounted on a larger aluminum plate than it was in Fred's setup, but I don't think that matters too much since the lasers are on their own, suspended tables, and those haven't changed.

David:

I took your advice and twiddled the current adjustment pots inside the driver board. (With the power off!) I actually moved all 4 pots: the current limit, the current setpoint for the diode, the temperature limit, and the temperature setpoint pot. I made sure to move each one back and fourth about 1/4 turn each way several times before returning them to the exact positions they were when I started. Then I fired up the laser and checked current draw and power output again. No difference from before. (dang!)

I also checked the blanking wires where they were soldered to the driver board. While the wires themselves are thin gauge, the solder joints were clean and solid. (There goes that idea...)

As a final "college try", I nerved myself and removed the cover on the driver board again. Then I powered up the laser and let everything stabilize. With a cringe on my face, I slowly adjusted the drive current pot and watched the current draw. After nearly 1/2 turn, there was almost no change on the total current draw, so I backed it off to where it was. Then I tweaked the current limit pot about 1/4 turn and tried turning up the drive current again. Same thing - no change in total current draw (apart from a few hundredths of an amp that seemed random) and no change in output power. (Still 40 mw)

At this point I lost my nerve, so I set everything back where it was and put the cover back on. Everything still works as it did before, so I'm happy to report that I didn't make matters worse! But I'm no closer to solving the problem either...

Aaron:

I hear you buddy! But things aren't as bad as they sound. The rig looks pretty darn good even with less than half the amount of blue that it should have. And since this is the first fully-controllable RGB rig I've owned, I'm pretty pleased nonetheless! But it will be great to get the blue working 100% again. (Hey, at least my back is feeling better...)

Adam

[marconi]

I agree with David and Doc...
Sounds like a TEC issue or dirty pot , Geez that reminds me of
something back about 25yrs ago...oh, wrong story

Well, anyway I have seen weakend peltiers and dirty pots (no pun)
on the CNi blues perhaps the lasevers suffer the same.
I had to change the peltier out in my 150mW blue when its output dropped
down to 40mW or there-abouts. For a while I got away with readjusting the TEC pot. but eventially had to change the peltier after a while.
Now , it sittin at 175mW stable at the same diode current.

I guess the only thing todo is to measure the diode block and cavity temp. but that would mean opening. or you could measure the associated currents
that may give a clue.

I can say., I also own a 150 CNI blue that I did everything I could for but in the end ..It turned out to be bad crystals.

Hopefully you wont have to ship it back.

Edit: posted about the same time.
Strike the dirty pot idea

Its all guess-work from here ,you'll need to do some seperate current measuring.
could be just about anything..bad diode drive or TEC drives...
These things are very touchy

[buffo]

Hi Chuck;

Thanks for the reply. Yeah, I was thinking either bad TEC driver or bad diode driver. However, in order to measure separate currents I'd have to wire up some sort of jumper between the cable to the head and the connector on the driver board. But due to the danger of static killing the diode, I really don't like the idea of unplugging that cable! With my luck I'd end up blowing the diode, which would kill my chances with a warranty repair.

It sounds more and more like this laser is going to have to be returned to China. But it's nice to know that folks here agree with Fred's assumption (and mine too) that the problem is in the driver board. (I think the drop in current draw is the smoking gun.)

Adam

[The_Doctor]

I guess the TEC isn't the answer, except indirectly. Modehops or erratic behaviour would give that away, so if they aren't happening, the TEC is probably fine, and probably the crystals too but I don't know enough to pass any kind of serious judgement on crystals (bought two, can barely see them let alone figure out the tooling I'll need to use to handle them). If the diode is drawing less power, the TEC circuit will also draw less as it maintains the right temperature. I don't know why that diode current drops though.

Do you know if it's drawing less than it did at that output when the mod input set it there when it was working right?

Edit: Sorry, I guess is on/off blanking, not analog proportional.

[marconi]

Yep.., Understand

I'd send it back too..
They have a pretty good service rep.

At least it acted up before the warranty period expired.