This unit was build ( in 1975( for replacing the phase effect created with two tape recorders.
Broken or bad LDR. The synton phaser uses special selected Philips LDR. If these are broken you must find an other LDR. I have used as replacement the VT935G these fits in the blackbox. The Philips version is better (larger range 2k-1M) but not availlable anymore.