Neumann U47FET Clone: D-U47 FET Microphone Project PCB Build thread

[JamieOxford]

Hello, I'm repairing an early STAM U-47 FET for a friend and it turns out it uses these DU47FETi PCBs and what looks like the 3U capsules mentioned here.

It's having some problems with popping every 5-10 seconds (it sounds like the phantom power is disconnecting continuously so I'm assuming it's a bad capacitor or component). Does anyone have any experience with this?

The circuit on the mic looks slightly modded to accommodate the lack of pad and HPF as well.

Please find a few photos attached. Thanks!

I've replaced R1, C1, C2 & C3 on the STAM which has reduced the amount of popping but the pops are still happening and I'm now not getting anything from the capsule. (I think the polarisation voltage is too low for any output but not sure where to go next.) I've traced a voltage drop at T3/R9 and a transient pop (negative voltage) at R9/T5 but not sure what could be causing it as the circuit is very interconnected. Can anyone help with suggestions of what the cause might be? (I've attached the original FET47 schematic which is almost identical)
Thanks!