Again one step forward and two steps back (well maybe only one step back).
As described in my April 29 post, I changed the flex cables from 1 mm pitch to far more flexible 0.5 mm pitch cables. This change was a big improvement and the ladder attenuator cube is now resiliently mounted. Even without the vacuum the attenuator is very quiet because there is no mechanical transmission from the relays to the outside world.
I thought I was home free - well not so fast.
0.5 mm flex cables at both ends of the attenuator.
To install the new cables I had to desolder a small PCB from the vacuum cable feed through. I call this PCB “the pitch converter” because it allows the connection of a 0.5 mm pitch flex cable to the 0.1 inch pitch vacuum feed through. There are 12 connections and it is necessary to heat all 12 at one time to remove the PCB. Well it appears that applying enough heat, long enough to remove the PCB damages the Torr Seal epoxy surrounding the cable feed through pins. I confirmed this by trying one of vacuum chambers before removing the pitch converter PCB (it held vacuum as designed) and after removing the pitch converter PCB (it leaked).
“Pitch Converter” PCB.
The only way to fix this is to make new aluminum end plates and associated components. I now know what I will be working on next month…
This news is painful to the pocket book and more importantly another loss of momentum. I am really surprised how finicky and unforgiving this design is and flawless execution is required at every stage. There appears to be very few ways to correct any assembly mistakes without major re-work.
On the bright side I have tested all the design features of v2.2 at least twice and when I finally manage to assembly it without errors or last minute design changes the final product will be excellent.