- Found the inductor which shunts the positive input of MAX4107 was not touching the ground.
This left the positive input level undetermined at DC. This was why MAX had been saturated.
The PCB has a cut, so it was surprising once the circuit worked.
- Resoldered the inductor to the ground. This made the circuit responding to the intensity-modulated beam.
- But the resonances and the notches were totally off, and the 200MHz oscillation has resurrected.
- Attached 40Ohm+22pF network between the neg-input of MAX and the gnd. This solved the oscillation.
- Made the tuning and the characterizations. The PD is on Kiwamu's desk and ready to go.
More to come later
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I took REFL11 out from the AS table for a health check because it wasn't working properly.
The symptoms were :
- a big offset of ~ -3 V on the RF output. No RF signals.
- The DC output seemed to be okay. It's been sensitive to light.
I did a quick check and confirmed that +/- 5V were correctly supplied to the op-amps.
It looks that the last stage (MAX4107) is saturated for some reasons. Need more inspections.
At the moment the REFL11 RFPD is on the bench of the Jenne laser.
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