24NC31 Zenith, give me your thoughts...
 

This is the set that is shown in this picture, taken about a year ago:

http://img.photobucket.com/albums/v6.../65Zenith2.jpg

However, not long after the picture collasped and disappeared while in use. I haven't touched it since this week. Powering it up showed that it had lit tubes & dial light, but no HV or sound.

I found a belfuse on the chassis that was open.

Q: I don't know the rating of this fuse off-hand, but if it's something like 10 amp 250v, can I just use an automotive fuse (they're all 250v rating) of the same amperage and then re-enclose it in the little plastic box for safety & appearance?

Naturally I want to know why this fuse opened. The set had worked well after I did the convergence, but seemed to suffer from cornea-discharge more than usual. I attributed this to humidity in my basement, but knew that if I ran it for any amount of "real" time, I would have to clean out the HV cage.

Well there was more than the light fluffy dust inside... Rather a nice coating of tar & sh*%t. This prompted me to pull the whole chassis. I think this is pretty high-hour set, because most of the tubes, including the CRT are replacements. But at least I won't be dealing with and brittle PC boards! :banana:

Here is a look inside the cage:

http://img.photobucket.com/albums/v6.../TVs/zztv7.jpg

The red rubber layer of second anode insulation looks cleanly broken at the cage grommet. So clean in fact, that I question if this was a "normal" break in the insulation.

Q: Fix this, and how?

I only see 2-3 paper caps in the set chassis.

Q: Should I replace them? Are there more I should replace? What about the cans?

I'm really keeping this set around because I like the bezel design, and because I think this is Zenith's last roundie. However the cabinet is cheap, especially by Zenith standards, and I am hoping to someday find a "correct", electronicaly trashed set with a nicer cabinet.

In other words, it will be removed from the cabinet again at some point, but won't see regular use for a long time. I don't want to replace caps just to do it again years later.

The rest of the pics will be for before/after pics.

http://img.photobucket.com/albums/v6.../TVs/zztv1.jpg

http://img.photobucket.com/albums/v6.../TVs/zztv9.jpg

http://img.photobucket.com/albums/v6.../TVs/zztv3.jpg

http://img.photobucket.com/albums/v6.../TVs/zztv5.jpg

First project for the workbench I built more than a year ago!

http://img.photobucket.com/albums/v6.../TVs/zztv8.jpg

Almost forgot...

What do you think of this toasty looking transformer? I have a schematic, but have't really looked at it. What's the function and why so fried looking?

http://img.photobucket.com/albums/v6.../TVs/zztv4.jpg

The transformer is probably either a power supply filter choke or vertical output transformer. Did the picture collapse into a horizontal line before the set completely failed? If, so it is a fried vertical output transformer.

I have some used ones from Zenith color sets of this era if that is what it turns out to be.

Naw, the picture just faded away......:sigh:

carmine,
Ive had this same thing happen to a 25MC33 chassis.
you opened up the B+ fuse on that set, most likely due to a highly leaky filter cap. If the filter cap is in this condition, it will start burning up the filter choke. Im curious if the wrong fuse was in there. (that burnt up transformer you pictured is the filterchoke). the belfuse you need should be a zenith 136-66 (2 amp).
The one lead of the filterchoke is soldered directly to a filtercap. Its should be an 80uf@475v. Take it out of the circuit and test it for leakage. On the schematic, its C117B (hemisphere). The filterchoke helps smooth out DC ripple with the combination of the filtercap on the 350V B+ supply. Even though it appears burnt up, it may very well still be OK. If you test it, you might only read a couple ohms. Thats ok.

If it just faded away, and you've found an open belfuse, It could be in the LV power supply. It could be something simple like a bad filter, or your power transformer could be toast :tears:

Check the windings on the power transformer for shorts. Could also be a failed LV rectifier diode(s)

I have replaced the Belfuses with regular fuses mounted in fuse holders...they will not be as high as 10 amp, the Sams folder should say the value.
For the HV lead I have just replaced the whole thing with one salvaged from a junked modern TV.
The filter choke will have 2 leads only and I have seen several burned in this way...probably due to excess current draw from leaky electrolytics.

You may want to replace all the electrolytics in your zenith. The round color sets are old enough now that you can not get away with leaving any of them in use. If you turn the set on once a year you won't have to worry about the new ones going bad. If you can, Pick away at the burnt part of your choke transformer. See if the insulation is burned off the winding wires. If they are ok, You can leave it in there. If burned up, Replace the transformer. choke transformers are still easy to find.
Your zenith is a nice set.

Restuffing my cans
 

Looking over the chassis I envone only one paper cap in the vertical section. I want to replace the metal cans, but i have never done this before. I an going to unsolder one and take it with me to my local electronis shop. (i know, amazing we still have one.) and let them advise me. Will also check back here to see what anyone can tell me. Arent some of these actually two caps in one?

Some of the cans have one cap in it and some have more. {up to 4 } The problem is they can leak between the other caps in the can and cause all sorts of problems. One set I have, The old can cap was arcing in side of the can and blowing the fuse. {Never saw that before.}.
Also the more I see that burned choke transformer, I think you should replace it. Zenith is a good set, All that was going on and the picture was so nice and clear.

Ok, I found the 100 mfd Capacitor used in the vertical. . actually a box for $4. however, i removed a 160 mfd 250 volt 'paper can', that i think is connected to that burnt transformer. Can i connect more than one in series to get the correct mfd, so long as they are all over 250 Volt?

I believe you can connect multiple in parallel to get the desired rating. AES (tubesandmore.com) has the old multi-section twist lock cans, but they are expensive ~30 bucks a can. The only time I would actually get replacement cans is if I had NO room underneath the chassis for small electrolytics.

I usually leave the old cans in place (completely disconnected of course) for appearence, but put new ones under the chassis, just as jpdylon indicates.

Radio Shack sells small terminal strips that can be used to mount the new ones on(in some cases).

Yeah, not having to remove the can dawned on me right after i did one. Oh well, guess i will just reinstall it. So whats the verdict on stacking up caps to get the right value? if thats kosher, it would make it much easier. Parallel or series? Parallel makes sense, but i want the blessing of the old tv gods first.

Placing capacitors in parallel is additive. Two 30 ufd capacitors in parallel = 60 ufd. Of course, the voltage rating for both capacitors must be high enough for the application. I have done this several times using capacitors of equal voltage rating with no problems.

Placing capacitors in series is like placing resistors in parallel. The final capacitance value is determined like the reistor parallel network. Cf = (c1 x c2)/(c1 + c2). If the capacitors are equal in value, the final value is 1/2 the value of one of the capacitors, two 30 ufd capcitors in series = one 15ufd capacitor. This is usually done to improve the voltage rating of the capacitor network, not to increase capacitance.