Does anyone happen to have any documentation for a British Telecom "Tester 420A" ISDN BRI tester.

Also known as the T4200 - seemingly made by Fulcrum Communications in the early 1990s

It's throwing some error codes at me, and I'd really like to know what they mean!

#isdn #BritishTelecom #BT #telecoms #telecom #osmocom #pbx #telephoneExchange #telephonSystem