Of course, I played with all the trigger settings.
Once warmed up: It triggers OK on setting
Couplng: AC, HF Reject and Best on DC
Source : Normal and Chanel 2 ( I mostly use Channel 2 but Channel 1 has same behaviou)
Trigger mode: AUTO and Normal
A trigger : Slope Level ( tuned for vey low input signal levels (almost negligible).
So my operation of this scope is at should be (in my opinion)
However, if I shut down the scope and the R&S RC generator (set at 1 KHz) and power on the next day I get the secribed odd behaviour of this scope.
The R&S generator (albeit vey old 1960's) is not the culprit (checked with a 1960's Dynamco Nuvistor scope.
AS I said upon warming up, the TEK stabilises again to the condition, it had the day before before shutting down. This can take 15 minutes.
So, I was wondering whether this transient behaviour is normal (simply let the scope idle for 15 minutes) or whether something is starting to break down (I 'm thinking about leaky capacitors in teh power lines, tunnel diodes or whatever.
Should I really be concerned or simply leave it as it is: Strat the scope and have a coffee.
After all the vintage R&S valve equipment also ideally needs some 15 minutes to have fully stabilised.
Everybody, thanks for your suggestions!