CBM8032 - wobbly screen (The saga continues)

I have to disagree. What Adrian describes are the "classical" symptoms for electromagnetic inductions, resp. distortions caused by this physical effect. Grounding and shielding with tin foil does not help, since it's the transformers magnetic field (as opposed to an electrostatic field, that would be shielded by the grounded foil) that deflects the electrons of the CRT beam and causes the wobble. Tha most probable cause is indeed the transformer, more precisely: the aging core of the transformer. This core usually is made of a lot of thin sheets of steel. The purpose of the core is to a) couple the primary and secondary coils very closely and, more important b) to "contain" and keep the electromagnetic field closely within the transformer. Well, ok, that's a bit simplistic, but you'll get the idea. The core is not made out of a compact piece of steel since stray currents would be induced within the steel, heating up the core and wasting energy. This stray currents ("eddies" they're called in english, i think...) would be induced perpendicular to the orientation of the sheets the transformer core is made of. Thus, these sheets must be insulated by very thin layers of plastic or resin or something similar. Now, this is the point: With old transformers, this insulation starts to literally crumble away, which leads to a significantly larger stray magnetic field around the transformer. Later, you can usually **HEAR** this effect: the steel sheets start to humm with the line frequency. The transformer is close to dead now... To make this log story short: Yes, a new transformer should help. New, like in "factory fresh"... Even better would be one of these fancy and expensive torroid trasformers, since they have literally no measurable magnetic field outside the core. Shielding of the old transformer is no real option. You would need what we Germans call "mu-Metal", which is a special alloy of steel and other things i have long forgotten but that make it EXPENSIVE. It is magnetic, but not a good conductor, which make it ideal for shielding magnetic fields. You could try a shielding out of steel sheets, but they might get hot if the stray currents induced by the transformers magnetic field are too large. And the shielding effect is not too good... Oh, and by the way: I'm new to this list... 8-) Hi, i'm Michael and i am collecting old VAXen. I live somewhere in southern Germany, which is not that bad. No, really.... 8-) Cheers ms P.S.: sorry for the long post... Richard Erlacher wrote: -- Michael Schneider email (home): ms(a)silke.rt.schwaben.de Schleestr.8 http://www.vaxcluster.de 72766 Reutlingen Phone: +49 7121 492781 Germany FAX: +49 7121 479331 People disagree with me. I just ignore them. (Linus Torvalds)