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  #46  
Old 02-17-2013, 07:35 PM
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radiotvnut radiotvnut is offline
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I see '72 date codes on some of the capacitors; so, this set was likely made in late '72 for the '73 model year. The tripler is an RCA replacement with an '84 date code on it. It's highly possible that it's still good; but, it could certainly be bad. I always replaced the original defective Zenith triplers with either NTE, ECG, or RCA(SK) brands and never had one fail; but, anything is possible. If this were mine, I'd yank that tripler and focus divider and replace the whole thing with an NTE526 tripler; which, has a built-in focus divider. Those original Zenith focus dividers would change value, causing poor focus; and, they'd also crack and arc/snap like crazy.
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  #47  
Old 02-18-2013, 12:38 PM
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If I remember right, in the secondary circuit of the horizontal driver transformer, there is a resistor (1.5 ohms) and a small 15 volt electrolytic capacitor. Like the vertical chassis Zenith's, the cap drys out and the resistor burns removing a good deal of drive from the HOT. First sign of this is a foldover and a hot running HOT. Then a shorted HOT. I would always change those parts if they were original to prevent a headache. Also, but rare, a five watt resistor feeding the horizontal driver stage will open.
Looking at the flyback pictures, it looks like when the tripler was changed in the past the wre broke off the flyback and had to be resolded on. The flybacks, when failed, most the time developed a "hump" around the high voltage winding. That one looks good from the photos.
How do you tell a new tripler from the pictures? Easy! No silicone seal on the connections to prevent corona on any sharp bits to act as discharge points from the wiring.
And that set is HEAVY!!!! We called them 'Black Tops!" They always were upstairs which ment alot of cursing or FIX IT THERE!
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  #48  
Old 02-18-2013, 11:22 PM
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Quote:
Originally Posted by Eric H View Post
It looks like something's wrong with the Flyback, possibly burnt?
It looks like that red lead has been recently exposed at the end where it should be embedded in the tire.
What constitutes the flyback exactly? Is it the entire area between the 2 boards or is it the black area where the windings reside (or something else)?

The red lead actually had a piece of black electrical tape wrapping the area. It dried out and fell off exposing the area where the caulking/sealer is and the end of the red wire (since it was covered, it stayed of course cleaner than the rest of the wire shown).
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  #49  
Old 02-18-2013, 11:27 PM
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Originally Posted by DaveWM View Post
those safety caps look correct (replacements for the ones known to go bad, there should be a sticker somewhere on the back of the cabinet documenting the fix).
if you look carefully you should see the word "special" along with the part number.
The back of the tv has been exposed to sunlight for many years and the few stickers that are there are bare as whatever was written on them has long ago faded from UV ray exposure, unfortunately. I still plan to remove the bottom plate of the chassis to check the underside to confirm if there are any remaining caps there that were changed or are still the original(s).
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  #50  
Old 02-18-2013, 11:31 PM
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Originally Posted by kx250rider View Post
Looks OK, but the silicone rubber glob has been pulled off. MUST put a new glob, or there will be arcing (and a strong risk of RF burns to the hand anywhere nearby).

I think that flyback has an eye terminal on the windings; not embedded.

Charles
1) Do you think the electrical tape that has been there since the repairs were done back in the mid 80's has done the job of the silicone in preventing the arcing?

2) Is the eye terminal, that you mention, visible in any of my photos?
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  #51  
Old 02-18-2013, 11:38 PM
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Quote:
Originally Posted by radiotvnut View Post
I see '72 date codes on some of the capacitors; so, this set was likely made in late '72 for the '73 model year. The tripler is an RCA replacement with an '84 date code on it. It's highly possible that it's still good; but, it could certainly be bad. I always replaced the original defective Zenith triplers with either NTE, ECG, or RCA(SK) brands and never had one fail; but, anything is possible. If this were mine, I'd yank that tripler and focus divider and replace the whole thing with an NTE526 tripler; which, has a built-in focus divider. Those original Zenith focus dividers would change value, causing poor focus; and, they'd also crack and arc/snap like crazy.
1)Where do you see the '84 date code on the tripler? Not sure where to look.

2) Does the NTE526 tripled replace everything next to the horizontal output transistor that is vertical (the orange board and everything attached to it as well as the second board parallel to the orange board, etc)?

3) Is the focus divider located there too?

Thanks
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  #52  
Old 02-18-2013, 11:51 PM
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Quote:
Originally Posted by Zenith26kc20 View Post
If I remember right, in the secondary circuit of the horizontal driver transformer, there is a resistor (1.5 ohms) and a small 15 volt electrolytic capacitor. Like the vertical chassis Zenith's, the cap drys out and the resistor burns removing a good deal of drive from the HOT. First sign of this is a foldover and a hot running HOT. Then a shorted HOT. I would always change those parts if they were original to prevent a headache. Also, but rare, a five watt resistor feeding the horizontal driver stage will open.
Looking at the flyback pictures, it looks like when the tripler was changed in the past the wre broke off the flyback and had to be resolded on. The flybacks, when failed, most the time developed a "hump" around the high voltage winding. That one looks good from the photos.
How do you tell a new tripler from the pictures? Easy! No silicone seal on the connections to prevent corona on any sharp bits to act as discharge points from the wiring.
And that set is HEAVY!!!! We called them 'Black Tops!" They always were upstairs which ment alot of cursing or FIX IT THERE!
I will have to check the schematic to see where these components are. If they are damaged, are they externally visible or internal?
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  #53  
Old 02-19-2013, 08:49 AM
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It looks like a tripler retrofit was installed. If so, be happy. As mentioned earlier, the focus dividers (little white or yellow rectangles) mounted near the tripler would split open and hiss and then arc.
Can you hear a distinct "crackle" of the high voltage coming up when you turn the set on?
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  #54  
Old 02-19-2013, 05:55 PM
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Originally Posted by Zenith26kc20 View Post
It looks like a tripler retrofit was installed. If so, be happy. As mentioned earlier, the focus dividers (little white or yellow rectangles) mounted near the tripler would split open and hiss and then arc.
Can you hear a distinct "crackle" of the high voltage coming up when you turn the set on?
As I viewed the schematic, I believe it was probably the tripler that burst back in the 80's and repaired. I remember the repairman mentioned something about the HV and that back right corner was where the exploded remains of the tripler were. What is the function of the tripler exactly?

Have the original focus dividers been replaced here or are they visible in any of the photos?

I don't remember hearing any sounds at all when turning the set on but will check again.
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  #55  
Old 02-19-2013, 06:10 PM
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The tripler is a device that contains a bunch of diodes and capacitors. It's function is to triple the voltage that comes out of the flyback transformer. The flyback outputs around 10 KV and the tripler bumps it up to around 30 KV. From what I can see, it looks like the seperate focus divider is still used.
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  #56  
Old 02-20-2013, 03:20 PM
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Hey guys,

Does it appear to you that the tripler is not original in the photos below? One red wire in the back corner appears to have never been disturbed. I am also not sure, now, what exploded there back in the day but I do remember there was a lot of paper (like an exploded firecracker).



Also, could this have anything to do with the no video problem? Just noticed this ground strap from the chassis not attached under the CRT. Thanks.
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  #57  
Old 02-20-2013, 05:11 PM
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Quote:
Does it appear to you that the tripler is not original in the photos below? One red wire in the back corner appears to have never been disturbed.
Yes this tripler has been replaced. The giveaway is the "SK330x" part number on the side. The SK series parts were manufactured by RCA, and marketed as replacements for many OEM Parts. They published cross reference manuals so a technician could look up an original part number, and find the suitable SK series replacement. Sylvania/Philips (ECG series) and NTE electronics sell/sold similar lines of replacement semiconductors. Most independent TV repair shops used these universal replacement lines whenever possible, as they were cheaper and easier to get than OEM parts in most cases.

The red wire in the back corner of the tripler goes to the CRT anode. It wasn't "disturbed", because it is a permanent, potted-in part of the tripler module. A new tripler included a new CRT anode lead and cap in almost every case. The 3 other terminals on the tripler should have been covered with silicone rubber sealant when the tripler was installed, to prevent corona/arcing.

The original focus divider is still in place. It is the other plastic block looking component with 3 leads to the lower left of the tripler in your photo. The unused "F" terminal on your tripler is a focus voltage output, which indicates that the tripler incorporates an internal focus divider,, which isn't being used in your installation.

Last edited by N2IXK; 02-20-2013 at 05:30 PM.
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  #58  
Old 02-20-2013, 08:07 PM
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A capacitor is most likely what exploded and those white ceramic tubular caps were known to explode. When that happens, it can shoot pieces of foil and wax paper all over the place.
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  #59  
Old 02-20-2013, 11:45 PM
StratLou StratLou is offline
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Originally Posted by radiotvnut View Post
A capacitor is most likely what exploded and those white ceramic tubular caps were known to explode. When that happens, it can shoot pieces of foil and wax paper all over the place.
Since it was one or more of those white caps, then, it seems that the tripler was the only other component replaced. Would you agree? Still have to remove the bottom cover and see what may have been done on the underside of the chassis.

Also, any thoughts on the loose ground strap as a possible solution to the video problem? Haven't had a chance to reattach and not sure where to reattach exactly. Will try to pinpoint where it could've detached from. If anyone has any idea, please let me know. Thank you.
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  #60  
Old 02-21-2013, 08:29 AM
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Zenith26kc20 Zenith26kc20 is offline
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Those ground straps usually have a slip clip to go on the picture tube magnetic shield. I've also seen them ripped off of the CRT socket when someone was too lazy to replace a carbon trailed (arced over) crt socket.
Most likely the chassis was pulled and put on a jig for repair and the tech didn't see the ground when he reinstalled it.
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