No current on flexmod?

[Howie]

Hi,

I was just setting the current on the flexmod for my dual red and put the bias at ~25mA and when I go to set the gain, I show zero current and I don't know what I'm missing here.

To set the bias, I have the PSU ground, flexmod Gnd and Mod+ tied together. PSU +(12V), flexmod V+ and Interlock together. Flexmod -Out and +Out to meter set to amps. This works fine, set the bias then remove Mod+ and connect to 5V+ and tie the ground from my 5V circuit to the psu ground and flexmod Gnd. I get zero.

I checked my 5v source and it's about 4.96V. I checked my solder connections and they're good to go. To check my meter, I took another flexmod I set up for a 445nm diode and set it to run the reds just to see if it would reproduce the issue but that driver worked as expected.

Any thoughts on what I might check? I tried turning the pot 4 or 5 full turns clockwise and back and never registered a thing.

[chad]

Did you set the HI-LOW jumper?

chad

[Howie]

No, I thought the jumper was only set if you're using a 5V supply. I didn't set it on the first flexmod I set up anyhow.

The only difference is on the one I originally set for a 445 diode, I disabled the 7 second startup delay and the one in question I did not. I wouldn't think that would have any affect on setting the current though.

[chad]

Oh ok, It looks like you have one of the new flexmod p3 ones. The older ones had a hi-low range jumper.

Have you hooked up the interlock correctly? I don't have a new one yet So I can't help much. I am sure lava will be here soon and get you fixed up.

Double check the data sheet.
http://hacylon.case.edu/laser/FlexMo...dP3_Manual.pdf


chad

[Howie]

Thanks Chad

Yeah, it's the newer flexmod p3 and I have the manual right on the desk with me. I'm pretty certain I have the interlock correct, it's tied to the V+ power input coming in from the psu.

I'm at a loss right now as to what to try next. I may disassemble it and start over in case I have a dry joint in the soldering.

I'm off for the next week and the only thing I have planned is to get this scanner scanning. I should have the female db25 breakout board in a day or so then get the dual red setup tuned and square this driver away for the blue and hopefully that is going to do it.

EDIT:
Looks like I had a bad joint on the incoming Gnd wire so squared that away. Hooked everything back up to set the current and since I installed the other flexmod on the reds, I figured I'd set this one for the blue.

Set the bias to 200mA and with everything still powered, hooked the M+ to 5V and when I hooked the 5V source ground up with the modulation ground and psu ground, the current shot up to 2.55 AMPS! So as my brain is simultaneously processing the subvocalization of "Oh no, this can't be good", and sending the signals to the muscles to get me to reach down and unplug everything, the cylindrical resistor exploded.

I don't mean it burned out, I mean it exploded. I can confirm that burned components taste as bad as they smell by the way. After getting everything unplugged(not that I thought I was saving anything), and putting out the flames on the driver burning on my desk, I said to myself, "Self, this is probably why you had that nagging thought about wearing safety glasses".

Basically, I had a $40 dry solder joint....

[chad]

Oh wow! Kaboom. Sorry to hear that, we have all been there.
I am sure that Andrew will want to take a look at that driver. More than likely he can fix it for a reasonable cost.

That driver should have no problem modulating 4 amps at 50khz into a dead short. It will get hot, but it should survive it. If you haven't already disconnected it. Carefully write down exactally what wire went where.

Chad

[Howie]

I ordered a new one last night and if Andrew shows up here asking, I can explain exactly what I did. I knew when I started all this that I'd end up killing something being so new to the lasers and I think that's just part of the DIY thing.

I would however like to know WHY it did it so I can learn from it and not blow up the next one. I don't think this one can be salvaged but it's still around to serve as an example of what NOT to do.

Between this and my db25 breakout board being shipped to what I can only guess is a small fishing village outside of Lostinthewoodsistan, I may have to just go to work next week because at this rate, I'm not going to get this project finished as soon as I had hoped.

[drlava]

I was just setting the current on the flexmod for my dual red and put the bias at ~25mA and when I go to set the gain, I show zero current and I don't know what I'm missing here.

There's no way that a properly connected unit would not at least put out the bias current while you were setting the gain. That's a red flag here that something's wrong with your setup.

Reading through the rest, it's clear that there was a serious problem. Will check it out. It's hard to imagine anything that could do this except line power applied across the unit by a switched hot/neutral and otherwise miswired PSU that would allow a huge current to flow. 2.5A is not enough to cause such destruction, the driver can handle 4A safely.

[Howie]

There's no way that a properly connected unit would not at least put out the bias current while you were setting the gain. That's a red flag here that something's wrong with your setup.

Reading through the rest, it's clear that there was a serious problem. Will check it out. It's hard to imagine anything that could do this except line power applied across the unit by a switched hot/neutral and otherwise miswired PSU that would allow a huge current to flow. 2.5A is not enough to cause such destruction, the driver can handle 4A safely.

Thanks for taking a look and I'll get it out to you soon. I can't figure out the cause but then again, I'm certainly not the best with the electronics.

I used the same 12V psu and 5V modulation source for the other driver and it went real smooth so I'm lost. One thing that may help though.... When I was seeing zero current on the gain, I went back through my solder connections and I did have a dry joint on the Output return(-) and got that fixed.

Anyhow, thanks for your help and taking a look at my driver of shame.

[dash8brj]

when the output (dry joint) is open, the error led on the board should have come on.