zenith 25DC56 horz center - Videokarma.org TV - Video

DaveWM · #1 10-02-2010, 06:00 PM

Pic not centered, shifted to the left. I could not find any adj on the chassis or in the schematic, but there were several resistor and a diode in the path from the fly to the yoke (thru the pin cushion transformer). Maybe I should start by checking those?

DaveWM · #2 10-02-2010, 06:10 PM

did some more reading out of a zenith color service manual, says a shorted pin cushion primary could cause an increase in width. Come to think of it there is a bit of a pin cushion looking flaw on the right side as well. There are some small E caps in that primary side of the pin cushion as well.

radiotvnut · #3 10-02-2010, 08:36 PM

Another thing you may want to check are those white safety caps that connect between the collector of the HOT and ground. I think there's five of them. I think three of them are on the flyback and the others are under the chassis. It's possible that one or two have opened and it would be a good idea to replace all of them with Sprague orange drops of the correct value.

kx250rider · #4 10-03-2010, 12:32 PM

Mine (25EC58, basically same chassis as 25DC56 except for high voltage tripler and audio circuit), has had slightly too much width on the right side (nonlinear), since I got it at the Salvation Army in 1981. I live with it, but as you found, there is no adjustment for width or linearity. It didn't bother me enough to fool with it, but maybe someone else here has. That's about the best TV chassis ever built, and my opinion on that is shared widely here, and seldom if ever challeneged

You have a great set there.

And RadioTVnut is 100% correct: If yours still has the white ceramic safety caps, REPLACE immediately. May not affect the width issue, but if those begin to fail, the HV can soar, and actually arc over to the yoke and snap the neck off the CRT! Seen it happen many times.

Charles

radiotvnut · #5 10-03-2010, 01:38 PM

I'll give you another word of caution in the event you find one of the early vertical chassis CCII sets (E, F and G lines). The early ones had a single white four lead safety capacitor directly under the HOT heatsink. These caps would suddenly open, without warning, causing the HV to skyrocket and blow the neck off the CRT. If you find one of these early vertical chassis CCII sets, you'd be better off to open the back before you even try to power it up. If it has an orange drop cap, you're OK. If it has the white cap, don't power up the set until it's replaced with the upgraded orange drop cap. I'm sure 99.9% of the surviving CCII's have had the orange drop upgrade; but, there could still be some out there that still have the white cap.

At least with the flat chassis sets with the multiple caps, you have a little grace period before it goes BOOM! The newer sets with the single cap will be working fine one minute and go BOOM the next minute. That four lead white cap cost Zenith a ton of money in the way of replacement CRT's and possible lost customers.

sampson159 · #6 10-03-2010, 01:52 PM

they know what they are talking about.seen this happen once at the shop.they powered up a set and boom!breaker popped and the neck sheered off.white cap!mr dixon not only replaced the cap,but he installed a rebuilt crt at no additional charge.he called the customer and explained what happened.they were delighted that he was so honest about it.from that moment on,i,as fearless as i seem,stear clear of these white caps.i also steer clear of my ex mother in law with the same abandon!

DaveWM · #7 10-03-2010, 06:04 PM

I can see two orange drops (obvious replacements since they were j hooked on), and what looks like an orig plastic tubualr all by the HOT. I did not pull the chassis to look on the bottom.

DaveWM · #8 10-03-2010, 06:06 PM

you can see them here

http://www.videokarma.org/showpost.p...80&postcount=3

RobtWB · #9 10-03-2010, 06:14 PM

re: the chromacolor 25dc56 i recently aquired - or any 25dc56 chassis

are there no controls for width/linerarity???

the picture on the set i have is too large - looks like a 27" picture in a 25" screen - is it adjustable?

how good is a sams for this set? i have zero zenith service literature.

DaveWM · #10 10-03-2010, 06:51 PM

AFAICS no adjustments for width/horz lin.

the service manual I have does mention the shorted secondary on T209 (side pin reactor) could cause an decrease in width. if the primary shorts the width will increase.

It goes on to say that a temp short in the secondary is a way to test to see if the circuit is working (look for shrink).

I does not recommend shorting the primary but if it is shorted the R298 a 22k 2 watt resistor could be destroyed (primary of coil to 128vdc source).

So since the width is excessive on mine, I think I will check that resistor.

The 25DC57 chassis uses a transistor for side pincushion adj not the reactor like the 25DC56