Electronic Voltage Regulator Problems

[akharding]

I have a 1927 mag-engined car. Many years ago I fitted a Nik Plevan electronic voltage regulator, which involved  converting the dynamo to 2-brush configuration.  This worked well for a number of years but more recently has proved unreliable, with charge failing intermittently.  I had the dynamo rebuilt but recently cannot get the system to work at all.
My electronics guru  seems to think that the solid state regulator is impossible to test or repair, so I am contemplating replacing it. Any comments or recommendations.
Thanks in advance.  Andrew