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Thread: Spectra-Physics Millennia Vs SHG tower temp regulation problem

  1. #11
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    I can look Monday but Steveís right. Worked on my laser. Thatís one of two he mentions.

  2. #12
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    Default Flushing didn't solve the issue - any other info on disassembling the SHG tower?

    Quote Originally Posted by kecked View Post
    I can look Monday but Steveís right. Worked on my laser. Thatís one of two he mentions.
    Well, it's been a few months (thanks to Covid-19) but I've finally been able to flush the head. It didn't help, sadly - looks like I will need to take apart the SHG tower. Has anyone done this before, or seen any instructions on how to do it?

    Thanks

  3. #13
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    Default Spectra Physics Millennia Vs SHG regulation and head electronics issue

    So, having taken the plunge and disassembled the head optical assembly to get at the elctronic boad beneath (S-P in their wisdom made it impossible to examine or remove the electronics without removing the cavity assembly from the fibres and the Nd:YVO4 crystal assembly), I can report the following:

    1) There is no SHG tower in the Vs head - the liquid-cooled assembly is a gold-plated stand/clamp for the Nd:YVO4 crystal only.

    2) The SHG crystal, oven and thermistor are on the other side of the head, and not liquid cooled. They come off together with the cavity assembly, and are connected to the electronics board via a 4-pin plug (2 red cables: 65R, oven, 2 black: 10s of ks, thermistor).

    3) When there is a coolant leak in the head, which is certain to happen sooner or later as there are at least 8 hose connections in the head, the liquid comes into immediate contact with the electronics board.

    4) On the board, the thermistor connects to an LMC6484 op-amp. The analogue data is converted to digital by a PCF8591 and transmitted to the controller using an I2C serial interface (PCF8574). The SHG oven is switched on by a MOSFET.

    5) The board is relatively straightforward, the rest is concerned with things like power measuerement, shutter, emission lamp, interlock.

    6) On my board, corrosion caused by water has damaged/affected the SHG control circuitry (see photo). Unfortunately, the fault is intermittent and therefore very difficult to pinpoint. In addition, the board is inaccessible when working.

    It appears that from time to time on my board, the MOSFET for the oven stays on continuously - I can see the modes come and go as the SHG is tuned and detuned by the drifting temperature. If I disconnect the oven, the modes drift the other way again.

    I will try to clean up the board and replace the MOSFET for the oven, but I am not convinced that will make a major difference. In the meantime, if anyone has a head assembly 0452-6470 for sale, I would be very interested. I will also look into having separe, external control of the SHG crysral temperature.

    Merry Christmas and may your photons be the colour you seek and plentiful!

    Click image for larger version. 

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  4. #14
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    Quote Originally Posted by iggythebrush View Post
    So, having taken the plunge and disassembled the head optical assembly to get at the elctronic boad beneath (S-P in their wisdom made it impossible to examine or remove the electronics without removing the cavity assembly from the fibres and the Nd:YVO4 crystal assembly), I can report the following:

    1) There is no SHG tower in the Vs head - the liquid-cooled assembly is a gold-plated stand/clamp for the Nd:YVO4 crystal only.

    2) The SHG crystal, oven and thermistor are on the other side of the head, and not liquid cooled. They come off together with the cavity assembly, and are connected to the electronics board via a 4-pin plug (2 red cables: 65R, oven, 2 black: 10s of ks, thermistor).

    3) When there is a coolant leak in the head, which is certain to happen sooner or later as there are at least 8 hose connections in the head, the liquid comes into immediate contact with the electronics board.

    4) On the board, the thermistor connects to an LMC6484 op-amp. The analogue data is converted to digital by a PCF8591 and transmitted to the controller using an I2C serial interface (PCF8574). The SHG oven is switched on by a MOSFET.

    5) The board is relatively straightforward, the rest is concerned with things like power measuerement, shutter, emission lamp, interlock.

    6) On my board, corrosion caused by water has damaged/affected the SHG control circuitry (see photo). Unfortunately, the fault is intermittent and therefore very difficult to pinpoint. In addition, the board is inaccessible when working.

    It appears that from time to time on my board, the MOSFET for the oven stays on continuously - I can see the modes come and go as the SHG is tuned and detuned by the drifting temperature. If I disconnect the oven, the modes drift the other way again.

    I will try to clean up the board and replace the MOSFET for the oven, but I am not convinced that will make a major difference. In the meantime, if anyone has a head assembly 0452-6470 for sale, I would be very interested. I will also look into having separe, external control of the SHG crysral temperature.

    Merry Christmas and may your photons be the colour you seek and plentiful!

    Click image for larger version. 

Name:	S-P Mill 1.JPG 
Views:	5 
Size:	2.08 MB 
ID:	57485Click image for larger version. 

Name:	S-P Mill 2.JPG 
Views:	3 
Size:	2.27 MB 
ID:	57486
    maybe try reflowing the board or reworking by hand. Looks simple enough. If that doesnít work try continuity testing as you flex the board. Might be a lifted trace from the corrosion. Those two will solve bridging, tin whiskers, and cracked traces. If still out itís a bad component. You might try the old freeze spray trick too.

    wonder if you can rtv pot the board when done to prevent further water damage? Heck even slide into a plastic static bag or kapton sheet.

  5. #15
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    Default Sorted

    Thanks Kecked,

    All sotred - board cleaned, resoldered and everything back together. Running like new! Next stage will be the laser table, Tsunami and femtosecond pulses...

    Merry Christmas!

    Click image for larger version. 

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  6. #16
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    What are you driving as an expander compressor? Spitfire. Got an opo on it? We are doing second harmonic IR spectroscopy on ours. Glad you got it running.

  7. #17
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    Too late to be helpful, but I have those heads boards in the SP stash here. I plan to get all my SP service parts listed on eBay in the coming months.

  8. #18
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    Default Any left?

    Quote Originally Posted by Junktronix View Post
    Too late to be helpful, but I have those heads boards in the SP stash here. I plan to get all my SP service parts listed on eBay in the coming months.
    Hi Junktronix, you're never too late... leaked again... Do you have any of those boards left?

    Happy 2022!

  9. #19
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    I sure do. Drop me an email and we'll work something out. kevin@starlightphotonics.com


    Quote Originally Posted by iggythebrush View Post
    Hi Junktronix, you're never too late... leaked again... Do you have any of those boards left?

    Happy 2022!

  10. #20
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    Default The price of stupidity...

    So now I've done something really stupid - I tried to get the oven and thermistor out of the cavity, undid all the bolts/springs... and lost LBO alignment... I've tried all the usual tricks but the mounts are so poorly made (shape and tolerance inconsistencies meaning that there is friction interference in multiple places, complicated by the fact that the LBO housing can't be held directly because of the oven sheath around it) that there isn't a smooth rocking motion to be had anywhere, in any axis...

    Does anyone know how best to realign these shortened Millennia? None of the other optics have budged, so I'm assuming the 1064nm beamwaist is still in the right place.

    My next plan is to take the rear cover off and shine a torch/low power laser through the cavity to see if I can see anything at all...

    Feeling stupid...

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