I built a filter a few weeks ago and it works great. I told a friend of mine and he ordered and built a kit too.
He was not as fortunate as I was and his filter is dead! We've have checked the pcb for problems like soldering, wiring, etc and tested the regulator, the clock and the audio amp and they are all working fine but no signal comes through the filter, i.e. the SCAF chip is not working.
The only thing we can find that's out of spec is the Vreg/2 voltage. Vreg is 9 V but Vreg/2 is only 3.7 V. We have checked R17 and R18 and both are 10k. This is a mystery as a voltage divider with 10k + 10k should give 4.5 V.
However, according to the spec sheet the LTC1060 should work with a Vcc as low as 2.5 V. There must be another problem??
The following measurements were made with the LTC1060 removed. Coming back to the voltage divider R17/R18. The voltage over R17 is 5.3 V and over R18 it's 3.7 V?? Disconnecting R18 from ground Vreg/2 should be basically the same as Vreg but not so - it's only 7 V!!??
IOW, with the LTC1060 removed Vreg/2 is still drawing about 2 mA? We have disconnected C1 and C5 with no change.
73 Bert, VE3NR