While investigating ALS DIFF issues, we noticed that TEC controller for the ALS SHG failed 78 days ago. The crystal temperature is now about 8 degree C lower tnan before. Surprisingly, this made paractically no difference in the green power output. Both voltage an dcurrent readbacks are zero.
Maybe related to this.
We discovered that the 24V power supply lines running to the TEC driver were unplugged, so we reconnected them and everything works. We noted that when we powered the chassis up the LED's on the TEC driver board lit up indicating the power supplies were working correctly. We had not noticed these being active before disconnecting the supply, so these would have been a good indicator that the power to the board had been interrupted. I checked the other TEC driver boards and they all indicate good power.
F. Mera, M. Pirello