Schematic for P.I. Hi-Power Goldquest

[nalag46]

Hi Reg,
Job is done. After replacing the two negative voltage regulators, power was restored to the board but I found that nothing was coming out from the main board. I checked the 5v positive reg. which was not energised due to no feed from the 555 ic generator used in this circuit and after replacing it, everything came back firing in all cylinders. All of these components failure plus a pair of fuses were caused by a careless individual connecting the wires on the power plug the wrong way round, which brings me to one more question; why the need of having a 12v wire from the power board being connected through the 3 pin plug to a dead terminal on the battery power socket?
I am very grateful for you help and advise.
Ton

[kt315]

GQ SS is newest eric foster's detector, last from ones, while minipulse is old and from first one. thank you for photos.
geotechers have to begin to learn modern eric design, this is my point of view.