Hi guys,
I just repaired the second Tek 7854 that has been sitting under my table for a while now. The previous owner tried to to repair it and probably exchanged the position of a few mini-coax wires which resulted in no beam on screen. So it ended upon ebay and I bought it for cheap. Since it wasn't working properly and I had no time to check everything, it ended beneath my lab table.
Recently I bought another supposedly dead 7854 for really cheap (250$ incl shipping from US to EU and with 7D14 counter). It arrived in great condition, worked beautifully, but was covered in a thick filthy nicotine-tar layer. So I disassembled it for cleaning and used it as reference to check the wiring in my other dead 7854. The position of some coax wire on the bottom of the digital mainboard were exchanged. Put them back in order and had another nearly fine 7854 in my Tek 7k collection.
Only problem are the shadows in the tube. Anyone ever seen something like that before? Position of shadow relative to the trace changes if the trace is moved up or down,with no shadow (shadow on trace), if the trace is centered on screen. The more vertical deflection, the greater the vertical deflection of the shadow.
This makes me think that it might be caused by unstable anode HV voltage, since a beam with less acceleration is deflected more. But I've also read that CRTs with gas inside show similar symptoms.
Just want to know, before I start digging into the HV section behind the CRT, whether someone has seen something similar and can guide me into the right direction. Deflection seems OK, no noise on it, since the display captured from deflection plates in X/Y mode on my 7904 is completely fine.