The problem is without a schematic of your particular regulator, there's no way short of opening up and unpotting it to know for certain. Have you contacted the manufacturer?
Your old regulator was built by Sean Hawker of CMES fame who stopped trading some 5 years or so ago.The manufacturer of the regulator ? The only information on that device is what can be seen on the photo of post #1. No make. I just ordered a DVR2 from DynamoRegulators Ltd. The comments (on internet again) are very good and the price is reasonable, so I'll find out soon enough. Fortunately, I have a magneto on the Rapide, so I can still ride it (now that "recreational" motorcycle riding is allowed in Belgium again.). Without lights though.
The attachment describes how to test an electronic voltage regulator.@ mercurycrest and Marcus: I found some information on internet:
When I connected both terminals W and AW together to the +terminal, and the -terminal to the earth, the dynamo was running fine.
Next, I mounted the dynamo to the engine again and measured the tension between A+AW and earth (battery disconnected) at "fast" tickover: 7 to 10 V. Is this test good enough to decide that the dynamo is ok and that the regulator must be faulty ? Is there an easy way to test the regulator ?
(Sorry, I don't know much about electronic equipment)