Chromacolor II blooming issue

[AndyMack]

Ok... I've got two sets down right now (other is a roundie), trying to get the easier of the two fixed.

It's one of the Zenith Avanti series, circa 1974 (?), white with the rosewood top, not a remote set. This TV has the following numbers on the sticker on the back cover, Model E4760, chassis 25EC58 (it's really faded, best I could make out). The chassis itself says 25EC83, looks original but who knows. This set was a one-owner, who claimed it was a good TV that only required a new CRT sometime in the late 80's.

Works well but the picture has a blooming issue, where the image gets larger with increased brightness, seems to go out of focus a little and whites will smear when the contrast is turned up to what would otherwise be a normal level.

I'm not very educated when it comes to TV repair, so I thought I'd pose the question here. Is this a simple module(s) replacement, or do I have to dig into the circuitry to fix this problem.

This set also has a noisy transformer (you can hear it hum when the room is quiet). Related or no big deal?

I love this TV, has great color and a sharp picture when bright/contrast is turned way down. Any advice is appreciated as always!

[radiotvnut]

Flip the service switch on the rear of the chassis to the set-up position. There should be a line across the center of the screen. If it is very bright, try turning down the red, blue, and green screen (G2) controls. These controls should be adjusted for a barely visible white line.

Also, check the 240 volts going to the CRT screen constrols. You can check this voltage at C270, a 10 mfd, 300 volt electrolytic cap. This cap is located under the chassis and should be close to the flyback side of the chassis.

BTW, that chassis is from '74 is was probably the best color chassis that Zenith made. What brand of CRT is in there?

[jpdylon]

Also check to see that the 24v regulated power supply is working properly and putting out a clean 24v DC under all picture conditions. Its normal for the picture to bloowm a little on high contrast scenes of the control is turned up a bit.

I believe 74 was the year before they started using the white HV regulator cap of death, but you might pull the back and check under the HO transistor heatsink. If you see a white 4 lead capacitor in there, stop using it until you replace it.

[radiotvnut]

I think that chassis uses several white HV caps connected from the collector of the horizontal output transistor to ground. It would probably be a good idea to replace these with modern capacitors of the same rating.

[kx250rider]

Originally Posted by radiotvnut

I think that chassis uses several white HV caps connected from the collector of the horizontal output transistor to ground. It would probably be a good idea to replace these with modern capacitors of the same rating.

YES!!! That chassis has (5) safety caps, Zenith part 22-5001. I think 3 of them are on the phenolic board on the flyback, and the others are below the chassis. If yours has white ceramic ones, they were recalled in the late 70s by Zenith and you must replace them to prevent the high voltage from escalating and possibly breaking the glass neck of the picture tube. In addition to CRT drive voltage problems (as discussed in some of the other answers) blooming is a symptom of too much high voltage, or poor regulation.

Charles

[AndyMack]

Wow. Good things to know! I will check for everything listed here after I get home from work tonight. Thanks!

[AndyMack]

Ok.. wanted to just check back and provide a couple of photos:

The chassis is in fact a 25EC58, don't know where the heck I got the other number (might be off my other Zenith).

Looked at the HV section - there appears to be something that has been removed. In the photo, just to the left of the tripler. Any ideas what that was?

Tube looks original. A photo of the sticker on the tube is provided, but I dont know how to decipher the numbers.

Will pull the chassis this week and check for the white caps. I've been hammered with unexpected overtime at work this last week, so haven't had a chance to really sit down with this set like I've wanted. Please bear with me.

[radiotvnut]

Some of those early solid state Zenith's had a seperate tripler and focus divider resistor. Often, one or the other would go bad and the technician would use the newer style (ECG523, 526, etc) tripler with the built in focus divider. I suspect that to be the case here.

I know how it is to get caught up in other duties; so, take your time. Lord willing, we'll be here when you get a chance to get back on it. I've got unfinished projects that have been sitting here for 15 years. I need to stop bringing home more stuff and fix what I have.

[zenith2134]

Nice set, Andymack! I'm not sure about your chassis, but it looks like a keeper for sure. Those had some very nice pictures on em.

I have unfinished projects invading my garage. A lot of them, in fact.

[radiotvnut]

Originally Posted by AndyMack

Ok.. wanted to just check back and provide a couple of photos:

The chassis is in fact a 25EC58, don't know where the heck I got the other number (might be off my other Zenith).

Looked at the HV section - there appears to be something that has been removed. In the photo, just to the left of the tripler. Any ideas what that was?

Tube looks original. A photo of the sticker on the tube is provided, but I dont know how to decipher the numbers.

Will pull the chassis this week and check for the white caps. I've been hammered with unexpected overtime at work this last week, so haven't had a chance to really sit down with this set like I've wanted. Please bear with me.

Oh yes, before you pull the chassis, see if that TV has a removable metal plate on the underside of the cabinet. Most Zenith's with the horizontal chassis had this feature so that the underside of the chassis could be serviced without removing the chassis. If you have to remove the chassis, make note of where each plug goes.

[sampson159]

the best set ever made! i also have a green label zenith crt and they deliver a sharp,crisp picture.great set.

[AndyMack]

Sorry to resurrect an old topic, but I'm only now getting to spend some time on these TV's again.

Flipped the set upside-down, removed the plastic pedestal and removed the metal access grille. Right off the bat, I have found what you guys were talking about (see first pic). What do I replace these 22-5001's with? I don't have a schematic on hand for this set.

Any other recommendations, while I have the chassis open? (besides cleaning it LOL)

[drh4683]

These are oddball caps. The replacement 22-5001 was a sprague orange drop, 715P series. The replacement cap does not indicate what the value is. It only indicates "sprague 715P Special construction". This cap is actually .0018uF@1600VDC. These are not available through sprague. I would assume the cap value was not printed so that techs would not install just any capacitor. With a part number only, you were forced to use just that part from zenith only, for safety and reliability reasons of course. The 715P series of caps are common and still made, so atleast you know the materials of the capacitor are not "special construction".

[TV Engineer]

The total value of those 5 22-5001 caps in parallel is the same as the 880-860 4 lead cap...which if memory serves me correctly is .01uF.

Anyhoo, all you need to do is remove all 5 of those caps, and install and 800-860 in their place.

At 1 end of the cap, 1 lead will go to B+, and the other will go to the collector of the horizontal output transistor. You will need to open the line that goes from the flyback to the collector of the HOT, and insert the cap in the circuit.

At the other end of the cap, 1 lead will go to ground and the other will go to the emitter of the horizontal output transistor. You will need to open the emitter circuit and insert the cap there.

When the original 22-5001 cap became unavailable (it came in bags of 5), we routinely did this in our shop with excellent results.

Another method I have seen others use was to twist the leads together at each end of the 4 lead cap, and solder it in place of 1 of the old caps (after removing all of the old caps.) THIS IS NOT RECOMMENDED! The idea with the 4 lead cap is that if it fails, it will open the path of conduction from either the collector or emitter, thereby killing the high voltage. The idea with the 5 original individual caps was that they wouldn't all fail at the same time. They did.

The 800-860 cap can still be found on Ebay.

To Charles...

Too MUCH high voltage will not cause blooming. Too little will. Too much will cause underscan of the raster and, sometimes, arcing in the CRT. A CRT's deflection sensitivity goes up as the high voltage goes down, hence the increased raster size with dropping high voltage. You are correct that blooming is caused by poor regulation, however. As beam current increases, it drags down the high voltage, and the result is blooming.

Good luck guys.

ETA... All of these, and other, safety caps are available here-

http://cgi.ebay.com/2-pcs-Hi-Voltage...2em118Q2el1247.

[Findm-Keepm]

Or get 5 safety caps for less:

http://cgi.ebay.com/Sprague-01uF-Ora...A1%7C294%3A200

Cheers,