[Philips210]

Hi.

Would it be daft to suspect a fault with the CRT or CRT socket? If one or both X plates were not making proper contact with the X amplifier, say just a capacitive coupling rather than direct, could this account for the loss of trace at low frequencies? Roger mentioned the possibilty of a weak capacitive coupling in post #5. This would seem quite plausible.
It would be good to be able to apply a range of voltages and polarities to the X plates to rule out the CRT.
As I mentioned before, the problem occured after about 7 minutes use. Switching off for several minutes, reapplying the supply and all was well again. This repeated a few times but now it's permanently faulty.

I checked again the ramp signal at the input to the X amplifier at R707 and on one of the X plates and the waveforms closely match apart from obvious differences in amplitude.
I also thought about the possibility of a fault on one of the three boards associated with the digital storage possibly affecting the blanking of the signal.

It's a complex oscilloscope complicated further by having the digital storage. I'd really like to get this working again but the service information is very limited. Some useful waveforms and voltage test points wouldn't have gone amiss.
I don't suppose any member has the same oscilloscope and has taken various measurements around the timebase and X amplifier?

Regards
Symon