Chromacolor 14DC15 horizontal sync issues

[jbeary]

Hello All,

I have a Zenith Chromacolor 14DC15 that I really need help with. The problem is horizontal sync. It's intermittent and get's better after it heats up. I've swapped out the 6U10 with three others which all tested good. Then checked the obvious, the diodes and have been grasping at straws with checking and replacing resistors and capacitors in the horizontal circuit. I don't think it's the diodes because I figure that the set would never lock into sync if one were bad. I've been looking more at the tubes as well as the resistances. Now that all of the voltages and resistance measurements check okay, I'm freaking out. Anyone have any ideas? I've checked most all of the tubes and can't find anything weak or weird. Don't know why this would sync up after it's warm but not when cold.. sync's up but barely and the AGC knocks if out when fiddled with or the channel is changed. Generally this is a resistor or capacitor issue, but like I said, I have no idea because they all test good when cold. Otherwise, CRT tests real good and it has a super picture, just a little mis-convergence. If anyone has any helpful hints, I would be very thankful to hear from you. I'm thinking that I should replace or at least check the horizontal output tube. It's original and you guys probably already know that it's glued into place. Looks like I have good output but no sync so please let me know if you have any ideas. Could this possibly be an electrolytic as well? All of these seem okay to me as it was brought up slowly!

Thanks,
Jeff

[Chad Hauris]

I think this would be a good time for the scope...when you have verified DC voltage measurements you need to check that the AC signals are OK. I would check and make sure there are sync pulses going into the horiz. section. The output tube should not have an effect on sync.
If this is the 4 tube model I have seen effect of bad electrolytics in several of these so it would probably be good to check ESR on the power supply filter caps or just replace them.

[drh4683]

the 14DC15 is a 16" portable color hybrid set. Has something like 14 tubes or so. I have a few of these and have never had this type of issue, so I dont have a specific answer. Since you mention it gets better as it warms up, that means its a thermal problem within one of the components. Get some electronic freeze spray. give each cap in the horizontal frequency section a shot while its powered up. Problem will be revealed once the set reacts to the cap that was sprayed. It works very well for finding the troublemaker. good luck.

[drh4683]

the 14DC15 is a 16" portable color hybrid set. Has something like 14 tubes or so. I have a few of these and have never had this type of issue, so I dont have a specific answer. Does the picture tend to slip sideways, or does it go off into tearing lines (like the horizontal hold was adjusted way off)? This set uses individual phase detector diodes. Did you disconnect them from the circuit before testing them? One could be leaky. However, Since you mention it gets better as it warms up, that means its probably a thermal problem within one of the components. Get some electronic freeze spray. give each cap in the horizontal frequency section a shot while its powered up. Problem will be revealed once the set reacts to the cap that was sprayed. It works very well for finding the troublemaker. good luck.

[jbeary]

Thank you fellas.... It sounds like I should go through the exercise of changing the electrolytics or maybe invest in an ESR meter at least. I have a scope but I'm not ashamed to admit I'm completely illiterate in using it. I did remove the diodes from the circuit before testing, but as far as I know, they work by allowing current one way and not the other and this simple test tells me that they are okay. Possibly I should look more closely at these Doug??? The picture does not start to slip, like if a tube was gassy or weak. It just goes haywire like the HH is just plain off. Like I said, I can lock in the HH after the set is warm, but it will go out of sync as soon as I change the channel or fool with the AFC. I do have freeze spray and will shoot the caps in the HH section, but shouldn't I be more concerned with the electrolytics at this point as Chad suggested? What tubes are in the four tube model??? From my Sams, it looks like these sets all had the same topology for their run.

Generally, I go through the exercise of changing all of the electrolytics completely out, but in a set so recent, I just brought it up slow although I admit that I have no idea what the issues were before I got the set. It's a curbside find, so to speak. I was hoping that I could get away more easily than that

THANK YOU ALL AGAIN! I'll post what's what as soon as I can get back to the bench.

[jbeary]

Hey Chad! My TV looks exactly like this one that's on your site!

http://www.picturetrail.com/gallery/...1904&members=1

If that at all helps you help me... THANK YOU AGAIN!

[wa2ise]

Originally Posted by jbeary

Hello All,
anything weak or weird. Don't know why this would sync up after it's warm but not when cold.. sync's up but barely and the AGC knocks if out when fiddled with or the channel is changed. Generally this is a resistor or capacitor issue, but like I said, I have no idea because they all test good when cold.
Thanks,
Jeff

Could be a capacitor in the horizontal oscillator circuit. One that's drifting in value as it warms up. DO NOT use a ceramic cap as a replacement, as those do drift too much for the oscillator circuit. Use an orange drop cap or such.

[drh4683]

which set is like yours? Are you referring to the 14DC15 beige cabinet one on the website?