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.

Please double check that paper can. if it was mounted on the chassis like the one you see in the picture it is isolated from the chassis ground.
When you install the new cap , Make sure it is wired in the same way as the old one and not touching the chassis ground.

As others have said, put the caps in parallel and there will be no problems. 160 was a popular value; with some hunting you can find both a 100mfd & a 68mfd. which will work nicely. Space can be tight under the chassis, especially if you are replacing all the electrolytics; you might have to get a little creative. You could also mount them on a terminal strip above the chassis if you had to but that isn't as pretty.

I have some spare belfuses if you want to go that way.

I am having trouble finding the capacitors I need for this Zenith set. Here are the sizes I need to replace the "cans". There was only one paper capacitor in the set (vert) and I've already done that one.


(1) 200mfd 25v
(2) 160mfd 250v
(1) 100mfd 475v
(1) 80mfd 475v
(2) 50mfd 475v
(1) 40mfd 25v
(2) 4mfd 475v

The problem seems to be the 475v rating. I find plenty with a 450v rating, but nothing higher... At least at my local radio shop and on Moyers.

Where should I buy them? :scratch2:

Check out justradios.com They have 500v caps in those values. Great place to get caps. You can use the "shopping cart" feature if you don't want to e-mail them an order form.

Justradios.com has only 10, 20 and 40mfd sizes in the 500v section. I'm just going to have to put a bunch of these in parallel aren't I?

What about my two 4mfd 475v? Put four 1mfd orange drops together?

I had the same problem in this thread: http://www.audiokarma.org/forums/showthread.php?t=89849 I still haven't decided what to do, and I was just trying to sort out all the references I got in that thread this afternoon. From the different places suggested to me in that thread, this is what I found: 100mfd-500v snap ons at http://www.alliedelec.com/Search/Sea...6787804769617F. But snap ons never look very good mounted on terminal strips under the chassis, so I'm thinking about replacing 2 of the original cans with those JJ multi-section caps mentioned earlier in the thread: one 50/50 - 500v and one 100/100 - 500v (also using one of the 100s for the 80, and one of the 50s for a 50-450v), they're at www.tubesandmore.com (to find them, they're under multi-section caps - not electrolytics). It won't look totally original, but it might look better than the snap-ons. As far as the 160mfd-250v, www.mouser.com has them (160-350v) but they're 12 bucks a piece. As far as the 4mfd-475 nobody seems to have them, I might just try replacing them with 10mfd and see what happens. I haven't actually ordered from any of these places or tried any of these yet though. I have 15 or so sets here that need recapping so I'm going to order up lots of caps in the next few days, from all these places justradios.com seems the cheapest, so I'll probably try and get what I can from them. I also remember from my earlier thread that the sprague electrolytics were highly thought of, so it might be worth seeing who has those specifically. I don't know, I'm confused, I used to get all my caps from a guy with a shop about 5 miles from here, and life was easy, but he closed up shop 2 years ago, and my stash of caps has run out.

Geez, I didn't think finding them was going to be such a PIA. Everybody is always "I recapped this set before breakfast and did the convergence after lunch"... Cripes, I can't find half the stuff I need to even get started. Ordering from different sources is just gonna net me a bunch of needless shipping charges.

450's will not be a problem. B+ in that set doesnt go over 390 V. Even when you turn on the set, the B+ will not surge over. You still have a 60 volt over buffer zone. The 450's are plentiful and cheaper. Win win situation.

That would certainly open up a lot more choices.

Any reason I can't use a 100mfd 250v cap, + two 30mfd 450v caps to replace:

160mfd 250v volt

OK, FWIW here's what I ordered. If anybody wants to check it over for mistakes, be my guest.


Item Name: 40 mfd at 160 Volts Axial E-Cap (1)
Quantity: 1

Total: $1.19 USD



Item Name: 50 mfd at 450 Volts Axial E-Cap (2 required)
Quantity: 2

Total: $6.98 USD



Item Name: 100 mfd at 450 Volts Axial E-Cap (Two 160mfds required, will add (2) 30mfds for 160)
Quantity: 2

Total: $7.98 USD



Item Name: 40 mfd at 450 Volts Axial E-Cap (One 80mfd required, two in parallel)
Quantity: 2

Total: $5.98 USD



Item Name: 30 mfd at 450 Volts Axial E-Cap (to be added to 100mfd)
Quantity: 4

Total: $7.96 USD



Item Name: 100 mfd at 50 Volts Axial E-Cap (2=200mfd)
Quantity: 2

Total: $1.30 USD



Item Name: 1.0 mfd at 630V Orange Dip ( (2) 4mfds required, will use 4 1mfd in parallel)
Item Number: DME105K630V

Quantity: 8

Total: $11.12 USD



Cart Subtotal: $42.51 USD
Shipping: $3.90 USD
Sales Tax:
Cart Total: $46.41 USD

Drh4683 is right, You can use 450 volt caps. If you still don't feel right about it, Hook up your volt meter and check the voltage on the caps. Turn your set on and let it warm up, Then cut it off. Hook up the meter and turn back on.
Then you will see the surge voltage when you turn it back on.
I did that when I did a recap on a zenith 29jc20 chassis. New caps can take a good amount of surge voltage. Also you can add up the value of a cap anyway you like. Just try and stay as close as you can to the original value.

If you all say it's ok, I'll give it a whack.

If my house burns down while I'm watching Green Acres DVDs, I'm coming to see youse.

:D

Put a fuse on the ac interlock and you won't have to worry about that.
It is not fun when the tv starts the house on fire. Been there..

I don't think 4 orange drops in parallel would work for a 4mfd electrolytic cap. Orange drops are not electrolytic. I don't think they are polarized even though they have one end marked. I think the mark just indicates which lead is connected to the foil in the cap. Then again memory isn't what it used to be either :) Unless they are controlling frequency most of those caps are probably not that critical value wise. I would use the closest value at the same or higher voltage. Only exception would be the 4 at 475 for that I would use a 450 volt cap.

Bill R

---

Wouldn't the non-polar orange drops pose a problem when being used in a circuit that has a polarized cap in it?

To replace a 4.0 mfd electrolytic capacitor with 4 orange drops, you would need four 1.0 mfd orange drops. The largest common value that I have seen is 0.33 mfd. It would take 12(0.33 X 12 is approx 4). of these which are fairly large in size.

How common are 1.0 mfd orange drops? The value 0.1 mfd is very common so possibly someone is getting confused. It would take 40 of the 0.1 mfd caps to replace a 4.0 mfd cap.

1.0 mfd at 630V Orange Dips are listed on Justradios.com

I've heard you all mention using them, so I didn't think stacking 4 together would be a problem to get 4mfd.

?

Same.

Replaced electrolytics in the I and Q signal paths in my recently restored CTC2. They feed the chroma signals to the matrix. Electrolytics were used by RCA in 1954. Today we have JustRadios and others supplying modern parts with modern dialectric materials:thmbsp:

See asterisks in the overall shot. Close up is 2C299 feeding the Q signal to the matrix at the red board.

Pete

Just to clarify: You can put non-polarized in place of polarized but you cannot put polarized in place of non-polarized. There are also some non-polarized electrolytics out there, I think for use with motors?

I have not dealt with justradios.com, so had not seen the 1.0 ufd orange(yellow in Petes picture) capacitors. I have used many of the electrolytics and the smaller size modern orange drops seen in Petes picture.

I have also replaced several 3 to 4 ufd capacitors, usually in the ratio detector of TVs. These are required to be 50 volts or so, so are easy to find. However, I have replaced some that require 3 to 4 ufd at 450 volts and had no trouble to date finding modern versions of these. I have some modern 33 ufd at 500 volt electrolytics that I have used when voltages above 450 are required.

As shown in Petes picture and mentioned previously, using non-electrolytics to replace small value electrolytics is not a problem when space is avaliable. I am at present working on a 1958 Philco Seventeener with all of the electrolytics mounted just between the bottom of the CRT and the chassis. I replaced all of the filters, etc with modern electrolytics. Space would have been an issue in a set like this if I tried to do otherwise(I had to remove the CRT to get to them).

If you don't absolutely have to have actual Sprague (Vishay) -brand Orange Drop capacitors, Mouser (www.mouser.com) has Cornell-Dubilier DME caps with 630V ratings with values up to 2.2 uF.

These are metallized polyester caps, and while I've never bought these in such high values, I must say I've been pretty happy with the ones I've used so far. I bought a bunch of 630V-rated versions (they're available in voltage ratings from 100VDC to 1000VDC) of these in several different values from Mouser a while back, and so far they've been nice. They're quite a bit smaller than Orange Drops-- the smaller size and the flatter shape of them makes them easier to fit in crowded areas (in my opinion). I like their overall appearance better too-- they're a muted dark brown-orange color that I think blends in more nicely with existing components in an old chassis or PC board a lot better than the bright-orange color of Orange Drops. They're also significantly less expensive. I don't know if their current handling is comparable to Orange Drops, but perhaps someone else here knows and/or has had experience with these..?

(Note: If you're trying to find these in the Mouser catalog (.pdf version is available on their web site), the Cornell-Dubilier DME caps are on page 671; they also sell Sprague Orange Drops, and they're on page 679)

I have also used the caps similary to those mentioned by whirled one in some applications. I have not had any issues to date. The 0.1 mfd value is the largest that I have used. The ones that I have used are dark blue, not brown, purchased from local radio club members.

Waiting for these caps to arrive is killing me.

Everything I order from Canada always looks like a bomb... Last summer it was a thermostat for my 1950 Kelvinator fridge, now it's a box of capacitors. I suspect this stuff is sitting in customs waiting to see if I'm on a "terrorist" list. I should have just stood on the banks of the Detroit river and had them float it over from Windsor.

Ugh.