CTC16 Focus Problem

[Jon1967us]

Now that I have my color back, thanks to locating an open jumper, a new problem has cropped up around the same time. It seems that maybe the 405v not having a full load may have overloaded some other part of the circuit and something got zapped, only I can't find what.

https://ibb.co/z7zYZhN

The picture is somewhat out of focus. Picture is very soft and only large type is legible. The focus issue started to be evident as the color was beginning to intermittently go out, and I did notice some arcing and snapping sounds, in the vicinity of the right side of the chassis. Unfortunately, that's as close as I can get to pinpointing where the sound came from.



Some findings and items:

Picture gets more blurry when brightness or color screens are turned up.

HV ostensibly regulates ok, with same 25KV at brightness minimum to maximum (very slightly varies)

Replaced R146, 1K a few weeks ago after it was discovered burnt.

Focus Circuit

Tested 3 different good testing 1v2's - all same result.

3-3.5KV maximum measured voltage on CRT pin 9. Cannot get to 5kv.
No shorted turns measured. Adjusting coil barely affects voltage reading.

R143 66M measured a little out of spec, around 55M, so I added two 4.7M 1W in series with it, but no change to focus.

Replaced X5 "Boost Rect" with NTE580 (original measured open on my DMM, although it's hard to tell if that means it's a bad selenium) Matched polarity of schematic symbol not "+" and "-". Pretty sure that's correct.

R139 4.7Ω across focus tube measured ok

R142, 4.7M measured OK

C90 130pF 6KV measured within spec and not leaky

Focus coil is adjustable. Cathode current goes up as focus control is rotated clockwise and vice versa, counterclockwise. Best focus is obtained in middle area of adjustment

Outstanding tests to be done:

Test R141 out of circuit

Test C91 in regulator circuit.

Have not performed the voltage drop measurement across R146 to regulator. I guess I would need to clip some leads under the chassis while it's still in the cabinet. I don't see any other way of doing it and not sure if it's necessary since I already changed that resistor

Obviously, the focus voltage is low. But I've run out of ideas as to how to boast it higher. Maybe the cause is the one thing left I haven't tested in that circuit, the 100k R141?

[SwizzyMan]

Have you checked the boost voltage coming off the cathode of the boost rectifier? Should be 1100v. I would think if that is low it would affect the focus voltage possibly.

[Jon1967us]

Originally Posted by SwizzyMan

Have you checked the boost voltage coming off the cathode of the boost rectifier? Should be 1100v. I would think if that is low it would affect the focus voltage possibly.

Thanks for the suggestion.
Measured the boost voltage at the cathode of the boost rect. and it was about 1150V on the VTVM

[Jon1967us]

Added note: Poor focus is present sans color as well.

[Jon1967us]

Interesting that the set runs much better-brighter with much better focus when run with straight wall/line current and not off the sencore powerite. I can set the sencore for 122v, plug the set into it and then will go down to 110 (I have a Kill-o-watt plugged into the sencore giving me readings as the meter on the power supply ist kaput. I think the sencore is rated up to 350w which is what the CTC16 is rated at. So at the top of the wattage, the power supply current seems to sag.

At wall current, HV stayed at 24-25 and focus voltage went up to 4kv ish.

[reeferman]

Don't discount the focus tube socket.

[Jon1967us]

Originally Posted by reeferman

Don't discount the focus tube socket.

Yes, checked the pins on the 1V2 at least a couple times.

Note, efficiency coil was frozen, so I dropped a tiny amt of deoxit in and due to its capillary action, I was able to unfreeze the slug. Eff coil was already set for lowest cath current. Also, adjusting the H-freq coil didn't affect cath current or HV either. Horiz is pretty rock solid anyway.

The focus problem is either due to faulty winding on the fly or the focus coil itself. Very limited ability to adjust focus. As I've prev stated, the boost rect voltage is fine, regulation seems to be working.