DIY modules, drivers and diodes

[drlava]

Hey Zoof, that must have been some hit to take out your laptop and DAC, sorry to hear that.
Have you checked/replaced the power supply? Those are often the first things to go due to poor electrolytic caps.

If that's OK, then check the input protection of the FlexMod. There's a small resistor on the bottom next to the input. With the driver powered off and driving the input only with 5V, both sides or the resistor should read about 5V. If one of the protection diodes has sacrificed itself, or the resistor is above 1k then that area is suspect. FETs in a control loop don't typically fail in the way you describe (modulation working, but low output).

Good luck!

[Zoof]

Hey Zoof, that must have been some hit to take out your laptop and DAC, sorry to hear that.
Have you checked/replaced the power supply? Those are often the first things to go due to poor electrolytic caps.

If that's OK, then check the input protection of the FlexMod. There's a small resistor on the bottom next to the input. With the driver powered off and driving the input only with 5V, both sides or the resistor should read about 5V. If one of the protection diodes has sacrificed itself, or the resistor is above 1k then that area is suspect. FETs in a control loop don't typically fail in the way you describe (modulation working, but low output).

Good luck!

Hi drLava,

Thanks for those pointers!

Powersupply is fine.
The voltage level of either side of the SMD resistor to ground is near 0.
The resistance over the resistor is around 2k ohm.
The diode conducts both ways.

So the problem is in this area.

Step 1 would be to replace the diode I guess - what ratings should be used? (since its sacrificial)
Any other things to consider at this stage?

thanks for the help.

[drlava]

You could desolder the black rectangular protection diode from the top near the input pin and replace it with a transient voltage suppressor diode with a standoff voltage above 5V, if that's the max you will drive the modulation. If you have adjusted the gain you'll want to take those laser diodes out of the output loop and turn the gain down to tune in your desired output current again. The driver will run without the protection diode on top if you want to test it .

[TheHermit]

These days you can buy an analog RGB module of decent quality at nearly the same cost at which you would pay for replacement parts.


Good analog drivers come from Poland and Russia... I'll get back to you with models, I'm out of the house today.

Steve

Hi Steve,
FYI, I contacted Vladimir several months ago to purchase his SimpleDrive v500mw drivers. But, unfortunately due to Ukraine, there is a trade embargo against trade with Russia, which killed the deal.
BR.
Roj

[drlava]

Just saw this in the forsale section, seems like a great deal. so you don't need to fiddle around with SMT repair.

https://www.photonlexicon.com/forums...-laser-drivers

[Zoof]

Thanks for the link! I might pick one up although the problem wasn’t with the driver but with the laser diodes after all.