> During investigations into the noise today by NH and OH a couple of findings were made on the grounding of the FEEs and Adaptor boards.
> 
> - The adaptor boards have no connection to the FEE ground over the ERNI connector
>    - Currently we are providing one via a ground cable between the FEE Al cooling and the Lemo ground on the adaptor board
> - The Al cooling plate is not electrically isolated from the copper plate on the ASIC and both are connected to the electrical ground on the FEE
>     - Verified with 0 resistance between plate and HDMI ground shield
> - The FEE is electrically isolated from the frame but when cabling is connected they show 0 resistance
>     - With electrics disconnected but water still connected they show 200kOhm
> - With the bias core going to FEE14 and the braid going to FEE8 better performance in FEE14 is obtained by disconnecting FEE8 adaptor board from the ground
>     - The cost of this is the rate of FEE8 goes up to 300k
>     - It is essential to have the adaptor board ground on the FEE ground but unsure why having both adaptor boards connected to their respective grounds makes one worse
> - The resistance between all FEEs is not zero. Some show a 5Ohm and some show a 35Ohm resistance between each other
>    

The adapter boards have ERNI ground pins, and the FEE64 has a grounded plane on its ERNI connector, unfortunately the orientation means the ground pins do not touch the plane on the FEE64 and hence no contact is made
Would require installing board "upside down" but then the ASIC connections would be wrong. A new adapter board layout would be necessary to correct this

Tomorrow will investigate direct connection of all FEE64s to mechanical ground via dedicated copper cable. 
Currently FEE64s get ground via Pulser(->NIM) ((weak ground)), HDMI(->NIM) ((possibly?)) and Power(->PSU) (primary grounding)
HV Bias is floating at NIM side and so does not provide ground path (intentional)
TD may have ideas to isolate pulser from AIDA FEE ground
Unsure if HDMI ground is a problem

The ground quality via the power may not be ideal over long cables of relatively thin wire. (5 * 20 AWG) and then unsure how ground of PSU connects to mechanical ground
Explicit grounding may help keep resistance between FEEs < 1 Ohm.

Will also mount a DSSD and see situation without pulser, with/without mechanical grounding and maybe with various LK jumpers.