For the last three years I have asked several times on different forums and no one can seem to pinpoint my problem. Maybe somehow there is some leakage to the chassis or the rear board (has most of the CRT components on it) that is enough to affect the 5ADP* series CRTs, but is still within specs for the 5CP1 CRT.
What is odd is the fact that the CRT looses focus whenever a waveform is displayed. I do notice that the HV to the CRT does drop by about 100 Vdc when the intensity is full CW. Don't know if it is normal or not.
I am wondering if it may be leakage from the focus and intensity controls to the chassis given the originals were mounted using an insulator to isolate the variable resistor case from the chassis and the knobs were mounted to a plastic shaft. I am gonna check for cold solder joints and places where HV leakage could most likely occur soon as I can get to the scope.
I say the 5CP1 works ok, but I ma not entirely sure as it's been ages since I have tried it. Still doesn't explain why the 5ADP* series CRTs do the same in the unrestored 304H. I can maybe take pics of the inside of the scope tomorrow if that will help.
Now I can connect another 5ADP* series CRT in parallel with the one in the scope and I get proper focus.
Here's a couple pics of my problem. The CRT installed still has the QC sticker on it. I did quickly remove part of the sticker though.
Normal (camera makes trace look out of focus when it is actually pretty sharp) although focus control (bottom right of pic) has to be nearly full CCW
With waveform displayed (waveform very out of focus and focus control not moved from position in first pic and camera does make it look slightly worse than it actually is, but not by much).
