Hellllp! with my roundie!!

[veg-o-matic]

Okay, so I've been using my Zenith roundie (Laura) as my daily watcher for months now with no problems.

Last night, the picture started "undulating." Picture the way a flag moves in the wind, but the undulation moves up the screen rather than across.

What would cause this? Please don't tell me Laura's days are numbered!

[Steve K]

Veg:

From your description it sounds like the filter caps in the B+ supply. Does the picture pull in a bit from the sides when the wavy pettern goes through that spot?

Steve

[Chad Hauris]

I don't know if any of the round sets used a degaussing coil, but in several rectangular Zeniths I've seen the degaussing thermistor has gone open and caused a very wavy picture.
Filter caps though are the more likely suspect.

[drh4683]

I changed only the filters that needed to be changed. However, my NOS supply was from 1980!!! Perhaps one of my 24 year old capacitors is now defective. In zenith, a very common value is 80uF@450volt. Thats what I put in there, 2 of them if I remember correctly.

If the degausing thermistor was a problem, you would also see purple and green colors in the waving (as the magnet is not turning off, its always on)

From your description, the caps are bad. You can buy caps from mouser.com they are around $6 a peice. Not too many stores carry caps up in the 450 volt range. most dont stock anything after 100volt. Before you buy caps, bridge over the ones I put in one at a time with a similar value cap and see if the problem goes away. If so, thats the bad cap.

[Chad Hauris]

Also remember to change all caps in a can if any one in the can is bad...sometimes only one may appear bad, but the problem that messed up one of the caps can eventually affect the others.

[veg-o-matic]

Thanks for the help, gentlemen!

I ordered two of the 450V 80uf caps from Mouser today. Ugh. I thought I was finished with all this cap replacement and soldering and stuff once I got my Heathkit running. No such luck!

Gotta do this, though. My Zenith roundie is my daily watcher and I've not been using it so I don't break it. I'm missing all my favorite shows!* (No cable in the den where my Heathkit is. Should do something about that...)

Douggie: Can you give me a hint about where I should be looking for the caps in question? I'd like to only pull the set away from the wall once and get the job done in one fell swoop.

Hmmm. Maybe I should look at this as an opportunity. An opportunity to buy one of those "cold heat" soldering irons!

Bob

* Currently How Clean Is Your House? and In a Fix.

[drh4683]

I originally got that set from John Horvath (jshorvath65) about 2 years ago, maybe 3? Anyway, there originally was a metal grille beneath the set and was removed and never put back. A window screen was stapled underneath to takes its place by someone else, but you will need to pull that screen off and you will see 2 large blue capacitors. Theres nothing else like it in there, they will jump out at you, they are about 1"diameter by 3" long. When you get the new caps, just jump the leads over each cap while the set is on and see what happens to the pic. Be very careful as the wrong move will give you a nice 400volt blast of energy which will throw your hand back faster than you could ever immagine! A 400 volt B+ zap is much worse than a 25KV zap! After you jump the new cap, short the leads of the new cap together using the shaft of a screwdriver, or some other metalic object that will allow both cap leads to touch at the same time (fork, etc) to drain the voltage of the cap. You will see a blue spark and a loud snap sound. This indicates that the cap voltage is drained, however you should do that about 2 or 3 times as you will not totally drain the cap in one shot. Do this after everytime you jump the cap over one of the caps in the set.

Since the set will be on its top (so you can work beneath it) you will notice the purity will look very bad, this is no concern and will be back to normal once the set is back in its normal position again. You wont need to play with convergence or anything like that.

[veg-o-matic]

Originally posted by drh4683
Be very careful as the wrong move will give you a nice 400volt blast of energy which will throw your hand back faster than you could ever immagine! A 400 volt B+ zap is much worse than a 25KV zap!

Oh boy! Sounds like I'm going to be having a swell ol' time here.

I'll post a message right before I attempt this operation. If you don't hear anything from me for a while, send flowers

[veg-o-matic]

Well, veg-o-matic (the village idiot) strikes again.

A while back I got the first of the two new caps installed, which didn't fix my "flag waving" problem but I didn't expect it to, since I still had another to replace.

So I finally got around to replacing the second filter cap. Had my set upside down so I could work on it. Jumpered the new cap in place and looked to see if it made a difference. The picture looked a little better, so I soldered it in place (thinking "Lookit me! I'm just like Doug!") and hoisted the beast right-side up again.

Now it looks like crap! I swear the rippling is even worse than before! What does this mean? Do I have more caps to replace? And how the heck does one replace one of those "can" caps with the multiple parts? That's where the filters are, right?

Am I going to have to break down and buy the schematic for this and try to bluff my way through understanding it? Or is it merely a matter of adjusting something (IhopeIhope)? "Now that the caps are replaced, you just have to adjust the frammis coil until the vertical synchronization locks in with the horizontal output nebulizer."

Not that I'm holding out any hope...

And guess what? The Heathkit in my den is starting to show the same problem!

veg

[andy]

---

[Chad Hauris]

Also make sure the old cap's positive lead is disconnected from the circuit. If the old cap is hooked up electrically it will cause trouble. I mount a terminal strip under the chassis and hook up the single value replacement caps to it.
The ESR meter is a good tool to find bad electrolytics...our meter only cost $12 or so.

[Bill R]

While your problem sounds a lot like bad filter caps, there is one thing I would check first. The bending and weaving can also be caused by a heater to cathode short in a tube. This could explain why the picture got worse when you turned the set back over. I would start with the tubes in the RF and IF sections, but I would quickly check all the tubes, since a short in almost any tube could cause this symptom to some extent. Also check all ground connections.

Good luck, have fun
Bill R

[roundscreen]

Bob A 47uf cap at 450 v should run about 2.00$ I get mine at radio equpment here in buffalo. As far as value figure around 5 % higher or lower no more. When you figure out were the caps are in the chassis look at the bottom of them see if goop is leaking out of them. Do them first. Do one cap at a time and check the picture on the set. That way if something goes wrong you know were to go to correct it. When you connect the new cap DO NOT leave old one connected into circuit. Good luck ED

[drh4683]

Its ok to use a higher capacitance (such as 100uf in place of 80uf). Try to keep voltages the same. Obviously dont use a 250volt cap in a 450 volt place.
Its not advisable to use a higher voltage cap in a lower voltage circuit (such as 450 volt cap in place of a 250) Reason being, when a capacitor is not used to its full potential, it has the tendancy to dry out sooner. Best way to describe it, the capacitor is not being saturated with enough voltage.

Some caps in the cans are rated at 475 volts, its ok to use a 450 volt in its place. Voltage doesnt reach that high. The 24MC32 (your chassis) only has B+ voltage of 350 at the highest. (B+boost is different and generally lot higher voltage around 800volts. That doesnt apply here but just wanted to let you know)

If I remember correct, your TV is a 24MC32?????

In that case, these are the filter caps:

these two caps should not be grounded directly to the chassis:
160uf@250v
160uf@250v

These next two caps are grounded to the chassis
80uf@475v
100uf@475v

Im reading numbers directly off a factory zenith schematic. Look at the power supply section of the schematic and you will notice the B+ voltage can be read directly off the terminals of the filter caps.

Measure voltage on the lug of the 100uf@475 with the set on, reading should be 250v
Measure voltage on the lug of the 80uf@475v with set on, reading should be 350v

Small voltage variation is no problem. Check voltages in DC mode and see what you come up with first. This way we can pin point where the trouble is. This is the best we can do w/o an oscilloscope handy.

[bgadow]

You can mail order caps from www.radiodaze.com or from Just radios (I can't remember if his address is justradios.com? should be a link around here, or on antiqueradios.com) Radio Daze offers quick service; Just Radios carries a wide range of values. Both have competitive pricing.

For the 160mfd caps, I use a 100mfd in parallel with a 68mfd. I haven't found any new 160mfd caps. I've recapped a similiar Zenith and it wasn't too bad; you may have to be a little creative with where you mount the new caps so that you have enough room under the chassis. If you don't have any terminal strips see if you can order some of those when you get the caps. These make it a lot easier than just having things "up in the air". I have another similiar Zenith that is ready to recap and I thought about doing it now and posting the photos for you, but I'm not sure if I'm good enough to set any kind of example!