Zenith 25EC58 poor focus

[Carmine]

Oh frustration...

The new caps have been installed. HV is down where it should be (as is focus voltage per the "corrected" Sam's). Focus is now worse than ever. Best focus is now at the extreme clockwise (it was almost perfectly centered earlier). Whereas before, the picture was "watchable" it's now a blurry mess. Although, as before, lower brightness does improve the focus, but anything approaching normal requires an almost invisible picture.

Photos show a dark and "normal" screen HV readings





Beyond the safety caps, I did notice a 10mfd @300v cap right next to one of the "middle chassis" safety caps that had to be open, it pretty much fell apart in my hands. Luckily I have a decent electronics store at literal walking distance, so I was able to buy this cap in a 350v rating. I don't have my laptop/Sams nearby, so I'm not sure which circuit this involves.





I'd be inclined to think I really screwed something up except that by "specifications", (HV and focus V readings), I'm better than before. What gives?!

[zeno]

If it uses a focus divider start with that. They usually crack, bulge, change color or melt. There may be a kit ( 800-616 ) but you need to up sub
from the OEM 63-#### I can help you with that.

If no divider the tripler just has focus out ( to CRT ) and control lines.

The cap was probably the boost cap. It would get too much DC on it
if the HV goes high & it brews up. Keep it in mind. It is one of the most
common fail on ALL brands from apx 1978 til the end of TV. It can
cause MANY different symptoms.

C U Later
Zeno
LFOD !

[damen]

Use the high voltage meter to check and see if you get any voltage on the focus pin of the CRT with the socket unplugged. If there's leakage from the anode connector to the focus pin inside the CRT it can cause the focus voltage not to track with the high voltage. If you measure voltage, use a grounded clip lead and touch the focus pin, if it "pops", like discharging the anode, it may correct the problem.

[Carmine]

Originally Posted by damen

Use the high voltage meter to check and see if you get any voltage on the focus pin of the CRT with the socket unplugged. If there's leakage from the anode connector to the focus pin inside the CRT it can cause the focus voltage not to track with the high voltage. If you measure voltage, use a grounded clip lead and touch the focus pin, if it "pops", like discharging the anode, it may correct the problem.

I'll try this in the morning. You're suggesting discharging the focus pin like a 2nd anode if I read this correctly?

[Carmine]

The cap I replaced is number 270 in the schematic. 10 mfd @ 300v



It's an electrolytic, but I'm still not sure of the circuit yet.

I was always taught to trouble shoot by first looking at what has changed... I changed caps that tune the HV circuit, it brought down my HV and focus voltage. Now the picture looks worse than before when there were open caps. Seems to me the issue has to be related to that, not a coincidental new failure?! I will give that focus pin discharge a shot in the morning.

[Carmine]

I did try to discharge the CRT focus pin. No pop and wasn't able to read anything. No change in the picture.

I measured focus voltage again and it seems low, although this type of meter isn't exactly precise. As I mentioned earlier, the SAMS has a hand-drawn correction that says 3.5KV. One could argue this is almost 1/3 of the way to 10KV.

The focus divider isn't showing any physical issues. Are there other voltage points I should try?

[vol.2]

Originally Posted by Carmine

Seems to me the issue has to be related to that, not a coincidental new failure?!

Yes, you changed some stuff, but that doesn't mean that what you did "messed it up." In fact, your repair very likely just exacerbated a pre-existing issue.