I have a Philips PM3540 oscilloscope and I have a problem with it. The intensity of the beam on the CRT increases very bad. So, I have to reduce the intensity by volume. but the beam light is very high and the measurement of frequency is shown wrong. I think the problem is from the high voltage transformer and I heard some noises from it. When I knap with the screw to the transformer the intensity changes to the normal state for a second.
I download the user manual from the site. but it is only 37 page and does not have the service manual.
So, anybody can help me?