Schematic for a JDSU Mod 10075248 Controller ? / Possible repair ?

[Jem]

Hey Jem,

Don't feel too bad I did the exact same thing a while back! I was eager to see if they were working, and being unsure of their required voltage I used a variable switching power supply. Lesson learned. I still have the broken one, but the component that burned out on mine is different than yours. I just got back from being out of town for the holiday, but will take a look later and see if I can help. At least I can identify what burned out on yours, but it may be more than that though...

-George

Thanks George

As you can imagine, i'm absolutely devastated, I loved this little laser

In hindsight it was really stupid of me to try my new PSU out on something so important, but I guess at the time I just wasn't thinking anything could go wrong - Lesson learnt !!

Thanks for the offer Shrad. I'll wait to hear from George then at least we'll know what the component is and if it's easily replaceable.

Cheers

Jem

[hologeek]

Hi Jem,

The component burned out on yours is labeled 2E. I think its a capacitor, 20uF possibly. Maybe someone else can help identify it. I don't think its a resistor. You can see the ic that burned out on mine. Its labeled 4874 at the top, but I can't read anything else.

[Doc]

Hi Jem,

The component burned out on yours is labeled 2E. I think its a capacitor, 20uF possibly. Maybe someone else can help identify it. I don't think its a resistor. You can see the ic that burned out on mine. Its labeled 4874 at the top, but I can't read anything else.

Possible, but I would be surprised for a capacitor to blow out due to over current?

[shrad]

tantalum capacitors blow from overvoltage, then cause overcurrent by a shorted or very low resistance circuit

I bet this is a small value tantalum chip capacitor... I have some if needed and can solder them

same for the 4874 IC which could be a switching mosfet

I hope there is no more damage, but if tantalum usually it's like a fuse

[Jem]

Hi Shrad

Do you want to take this to PM and send me your address?

Cheers

Jem

[shrad]

I have received the JDSU laser from Jem and had a look at it

The small burnt component is a high speed schottky diode which I replaced with a slightly more robust model

I also glued back the body of the inductor, which broke due to a damage to the driver casing (surely the cause of the trouble)

I plugged the driver in and powered it a first time, to see the capacitor just under it blow in smoke (tantalum chip)

I then replaced the capacitor itself and repowered the beast... then the light came out of the system status LED

First red, second green, third pufffff, the same 4874 mosfet has blown to smoke...

I then contacted Jem to ask wheter he wanted me to pursue investigations or not, as the board seemed to go through a serie of cataclysmic events...

He told me the driver was already fried anyway, so I decided to tempt a mosfet replacement...

The only part I had laying around was one of those double mosfets in one SO8 package, soldered on an old hard disk... it was 20Go and had many bad sectors, so I extracted the octopode from it and carefully rewired it to the laser driver board

The process was a bit difficult because of the package not being identically connected, so I had to put some tiny wrapping wire to connect the gates and sources of the two mosfets parallel (the chance was the four pins of a same row were drains)

When I powered the driver again, same sequence of lights except the smell... I had a chance to have succeeded

I plugged the head, powered the driver again, and nothing... false alert, this thing only needs a mere 5 minutes to preheat

The laser runs fine now, not SLM because of heatsinking issues of the head or the driver, but it runs

In fact the first minutes of run are not stable in power, then 5 to 15 minutes of rock stable SLM operation, then mode hops to circular modes and/or weird high order modes, one of them looking like an old 5 cylinder plane motor (not very visible)

[hologeek]

Nice work!

Just curious how you are identifying single mode behavior? The extra ghost beams are due to these particular heads not having the extra 'beam shaping optics' compared to the larger ugreen heads. The Uniphase G30 (or G50 can't remember which these are) manual has a good description of this.

-George

[shrad]

the first pic is single mode, the second has extra modes in five groups of two or more fringes around the central mode (I know the two ghost beams are reflexion from the IR filter and other inside bits)

sometimes it will have two or three circular fringes around the main beam

otherwise, I have left the laser ON for at least 30 minutes and had no mode hopping with a heatsink under the driver and a fan blowing air through the fins

[Laser Ben]

I think he may be referring to the longitudinal mode.

[weartronics]

small burnt component
damage to the driver casing
blow in smoke (tantalum chip)
serie of cataclysmic events...
mosfet replacement
The laser runs fine now

Congratulations! That was quite an involved fix, but it is always worthwhile to see such a nice laser working again, instead of on the junk pile.