#16
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I replaced both integrators in my 25MC33. They caused the trouble you have. They are hidden near the vertical output transformer. My service manual is not here but I can look at it this weekend and get the values. They look like three leaded brown ceramic disc capacitors with yellow writing on them.
Check the plate resistor on the burst tube. The tubes can short and draw too much current and burn the resistor. If you can get a service manual, there are two test points that you have to ground to turn on (defeat the color killer) the color circuit and the other defeats the color afc so the oscillator can free run. If you don't get floating color bars after grounding the test points I would replace the color crystal first. You may need to go thru a couple if the first one doesn't help. Don't turn any coils unless absolutely necessary. They can get fragile with age. |
#17
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Quote:
Last edited by Arcanine; 10-01-2015 at 11:51 AM. |
#18
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Watch out for the horizontal efficiency coil near the damper tube. The plastic coil form can break at any time and the turns unravel. My initial fix is to thread some small ty-raps through the chassis to hold it steady in the short term. I might address this in a future post if I find something a bit more professional.
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"When resistors increase in value, they're worthless" -Dave G |
#19
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Quote:
The horiz. efficiency (sometimes called 'horiz linearity') coil is a super-critical component that if it fails, renders the whole set unusable. The failure mode is the coil form itself, which crystalizes with age and breaks, releasing the windings from their sharply-tuned resonance point. With the resonant point lost, the cathode current in the H output soars 'waay out of spec, which will quickly destroy the tube and possibly damage the flyback. There's an early version of this coil which is OK. The coil form is brown phenolic and does not disintegrate with age. Later versions ARE a problem. The coil form is easily identifiable as an off-white, semi-translucent plastic (nylon?) material. This is the stuff that disintegrates. Anybody with a newly-acquired Zenith roundie should take a look and see which version is used. Normally the coil is tuned to a sharp 'dip' point, using a milliameter in series with the cathode of the H out tube. If the set has the 'bad' version of the efficiency coil, there are also three coils on the convergence board using the same material, and are prone to the disintegration problem, but don't render the set unusable. |
#20
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I was looking at the 25MC33 schematic and noticed that there is a color on/off switch on the color control. I don't remember if it is a push/pull switch, or if it turns on when you turn the color control up. Don't overlook the simple things. I have never had to replace one of the integrators, sets were much younger then. They are just a resistor in the signal line and a capacitor to ground. My Zenith tuners rarely gave any problems and they are among the easiest to clean. Clean the channel strips and be sure the fine tuning system is working. There is a small gear driven slug that is located on the end of the channel strip. I have seen cases where this gets so far out that the fine tuning control no longer moves inside the channel strip. If it gets screwed out to far, it will just spin and not move in. You can get it back in by removing the channel strip and gently pressing on it while turning it to get the screw threads started again. Buy the way Zenith used to advertise the tuner contacts on those channel strips as gold plated.
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Audiokarma |
#21
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Gold Guard tuner....
I have a spare hold control with an intact form of the fragile plastic type. I plan to unwind it, take it to a 3D scan/print place to make copies (probably ~12) to sell, and rewind a destroyed convergence coil from another set onto the original form.....Just need life to give me a chance to get around-toit!
__________________
Tom C. Zenith: The quality stays in EVEN after the name falls off! What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4 |
#22
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Admiral addressed the natural nylon problem in some of their tall chroma coils and transformers - they would break up at the base - we always assumed it was from getting too hot, but they said otherwise - the nylon simply dried out - constant heat and low humidity was the problem. Funny how Zenith moved from phenolic and fiber coil forms to avoid the seizing problems that plague those materials, and created another more serious problem...
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Brian USN RET (Avionics / Cal) CET- Consumer Repair and Avionics ('88) "Capacitor Cosmetologist since '79" When fuses go to work, they quit! |
#23
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My cool forms are all white plastic. Am I in the clear?
__________________
This device isn't a spaceship, it's a time machine. It goes backwards, and forwards... it takes us to a place where we ache to go again. |
#24
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The pigmented white, non-translucent stuff is Okay AFAIK, unless somebody else has experience indicating otherwise.
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#25
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Here are the integrators from my notes. The number is printed on them. I made mine up from scratch and they work fine. If yours are different, let us know! Oh, both the resistors in the top one are 33K
Last edited by Zenith26kc20; 10-06-2015 at 02:01 PM. Reason: More info |
Audiokarma |
#26
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The no color issue, is most likely caused by a bad Colorburst crystal some are mounted in a glass tube and sum are mounted in a metal can check the schematic it will show you where it's at. Also I suspect you may have bad or leaky caps in the chroma section yet, most times when you have no color or you can't even tune in color you can usually adjust the peaking coils in the chroma circuit slightly and you should notice rainbow bars start to appear keep going until the rainbow bars lock into true color. It's kind of a down and dirty way to do it but techs used to do it all the time why hook up all the equipment when you have a fiddle stick.... also the no color issue can be caused by a dirty VHF tuner
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RCA VICTOR and its dealers bring you...... |
#27
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Quote:
Last edited by fsjonsey; 10-29-2015 at 02:08 AM. |
#28
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Integrators are disc shaped & have 3 wires. Early ones
were dark brown, later ones tan. Part number stats with 87- The rest of the number is a paint splotch on them. Color will match the resistor color code. So if you got orange paint its an 87-3 yellow 87-4 etc. Sometimes the factory manual or Sams will show the break down of values. If not there WAS a page out there that listed them all. Do not confuse them with 3 legged caps that Zenith used. They were blue or brown & had a 22- part number. Odds are the crystal is the wrong freq. so DONT go tweaking. Pull one out of a junker must be a 3.58###. 73 Zeno |
#29
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Quote:
Shango's page has the integrator values listed. http://boxcarcabin.com/integrator.html
__________________
This device isn't a spaceship, it's a time machine. It goes backwards, and forwards... it takes us to a place where we ache to go again. |
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