After increasing the laser power (klog35349), we attempted to resolve the mode-hopping phenomenon reported in klog35344 by adjusting the temperature of the main IR crystal.  This time, we unlocked the IMC before making the temperature adjustments.

Figure 1 shows the original IR crystal temperature before the adjustment: 46.5°C.  We first decreased the temperature by 0.5°C from the original value, but this made the mode-hopping phenomenon even worse.  We then tried increasing the temperature, but could not go higher because the dial had already reached its upper limit.  Therefore, we further decreased the temperature by more than 1°C from the original setting.  Figure 2 shows the IR crystal temperature after adjustment: approximately 45°C. Figure 3 shows the PMC transmission power.  Before the adjustment (at the right cursor), large fluctuations were observed.  After the adjustment (left cursor), the transmission power appears to have stabilized.

Following this, PLLX and PLLY locked automatically via their respective guardians.  However, the TEMP BIAS offsets for both systems increased from 1.0 to ~1.5.  In this state, the GRX temperature was 30.1°C and the GRY temperature was 27.2°C, as shown in Figure 4.  We set both TEMP BIAS offsets back to 0 and manually adjusted each temperature to the desired value.

Note: We modified the PLL guardian so that the scan now starts from -1 instead of –2, since we know the good offset is typically around 0.