Zenith 25EC58 poor focus

[Carmine]

Hello All,

I'm chasing a poor focus problem on my 1974 Zenith Piedmont (I've redone the speaker cloth on the left, haven't done the right side yet). This will be a daily-watcher in my family room when/if I can get it straightened out.



Here are a few things I know:

The set has some kind of "thermal" issue that gives a raster-only/no-sound until it operates for about 5 minutes, then suddenly the picture/sound will appear. I'd guess this is an IF issue?

The CRT passes all tests with flying colors per my B&K tester. It has plenty of brightness with no bleed/smearing. Colors look good.

The HV safety caps have not been changed. Apparently the part 22-5001 number was not revised during the recall which led to some confusion on my part. I do wish to replace them. My understanding is they are 18 microfarad @ 1600v. Some sources say there should be 5 in the set, but I only find 3... One under the chassis and two on the HV board. I've not found this exact rating, but perhaps I don't know the best source. Any help on that is appreciated. At any rate, the HV appears to be in the normal range.

On to the focus issue... Sharp picture only at very low brightness setting. (As you know, cameraphones make a picture look brighter than it is. This would actually be unwatchable in real life. It also isn't this blue.)



which corresponds to this HV reading



A normal brightness setting gives a blurry picture with some growth in size:



and this HV reading



The schematic (Downloaded from SAMS, complete with hand-drawn correction) says I should see 3.5 KV at the focus pin (I measured on the board)



At the lower brightness level I read about 5KV. Turning it up to the normal brightness level lowers it to about 4.5KV.

Any ideas where to check from here? I'll also mention that turning the screen controls all the way counterclockwise never extinguishes the picture. Even adjusting the brightness limiter never fully dims the picture. I don't know if this is related to the problem.