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!