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-   -   Testing a Yoke: Eico 944 (http://www.videokarma.org/showthread.php?t=270115)

Montman 02-09-2018 12:10 PM

Testing a Yoke: Eico 944
 
Testing my first yoke coil : Stancor DY-1 . My EICO 944 yoke tester instructions says in order to test it correctly, the shunt resistors across the coils have to be removed first. I haven't pulled the yoke yet, but are they the resistors in the yoke that have to be removed? Has anyone ever done this before? It tested bad when I did the vertical coils which have the shunt resistors across the coils.

Any advise would be appreciated.

Also, if it tests bad, anyone know where I can get a tested Stancor DY-1 for an Emerson 571?

Electronic M 02-09-2018 02:04 PM

There are usually resistors under the back cap of the yoke.
Honestly, unless I've recapped a set and it has deflection failure/serious defects I never bother to test the yoke...They don't fail that often, aren't too hard to find replacements for, and often if a designated sub is NLA one from a similar junker set will do.

Montman 02-10-2018 12:02 PM

Thanks for the advise. There was arcing snaps coming from the yoke vicinity and about a 1/2 second video drop out when it happened. The ballast tube recently blew after a snap and I'm trying to back engineer the culprit.

Polaraligned 02-10-2018 08:16 PM

If you are getting intermittent insulation breakdown on the windings, the 944 isn't going to pick it up.

Electronic M 02-10-2018 08:34 PM

Most sets run enough current/power through ballasts (which if not a sealed glass cased type tend to rust open) that if the ballast opens while the set is on then the point where it opens will arc/snap.

I agree with polar. Also if the aquadag coating gets close too the yoke it can arc to it in two circumstances: 1.) dag grounding failure (this is bad, quickly fix it if it is broke), 2.) Dag grounded, but too close to the yoke and yoke is arcing to it...This can be due to unnaturally high yoke voltage, or normal yoke voltage and insufficient insulation between things.

Some sets normally have a snap or 10 immediately after power up/power down...Snaps, after it has had a raster for 30+ sec, are where you should be concerned, and snaps that are extremely loud.

Montman 02-11-2018 01:10 PM

Thanks for the grounding failure information. I have a second set. I'll swap out the yoke and check the aquadag coating and ground issue.

Is there something I can spay or coat the aquadag near the yoke to prevent arcing?

fixmeplease 02-11-2018 05:08 PM

Quote:

Originally Posted by Electronic M (Post 3196062)
Most sets run enough current/power through ballasts (which if not a sealed glass cased type tend to rust open) that if the ballast opens while the set is on then the point where it opens will arc/snap.

I agree with polar. Also if the aquadag coating gets close too the yoke it can arc to it in two circumstances: 1.) dag grounding failure (this is bad, quickly fix it if it is broke), 2.) Dag grounded, but too close to the yoke and yoke is arcing to it...This can be due to unnaturally high yoke voltage, or normal yoke voltage and insufficient insulation between things.

Some sets normally have a snap or 10 immediately after power up/power down...Snaps, after it has had a raster for 30+ sec, are where you should be concerned, and snaps that are extremely loud.

Where do those snaps come from? My Philco does that at power up and i have never figured out where its from.

Sorry for bumping in here but I had never noticed that posted before. Thanks

Electronic M 02-11-2018 06:14 PM

Quote:

Originally Posted by Montman (Post 3196077)
Thanks for the grounding failure information. I have a second set. I'll swap out the yoke and check the aquadag coating and ground issue.

Is there something I can spay or coat the aquadag near the yoke to prevent arcing?

I would not coat it. If you must use plastic bag material for insulation, but please don't coat it. You see if the dag has any islands (patches that lost contact with the rest) they will arc to other parts of the dag...Coating them with an insulative product usually does not fix it, and instead makes it harder to fix the right way. Don't paint insulation on over the dag. Also some sets have a spring steel wire or loop of wire on the yoke that is supposed to contact the dag and act as the dag ground...Sometimes that will arc if it is not touching a good point on the dag...Moving it or making a better dag ground elsewhere should cure arcing from that.



Quote:

Originally Posted by fixmeplease (Post 3196081)
Where do those snaps come from? My Philco does that at power up and i have never figured out where its from.

Sorry for bumping in here but I had never noticed that posted before. Thanks

Often it is from internal parts of the CRT equalizing charge, it can also be related to the dielectric of the capacitor formed by the coated CRT walls discharging, or even static between the cabinet, CRT and HV system discharging.

old_coot88 02-11-2018 06:25 PM

Quote:

Originally Posted by Electronic M (Post 3196084)
Also some sets have a spring steel wire or loop of wire on the yoke that is supposed to contact the dag and act as the dag ground....

I've never seen it on the yoke but rather connected to the chassis or somewhere on the CRT mounting system.

Electronic M 02-11-2018 06:31 PM

Quote:

Originally Posted by old_coot88 (Post 3196085)
I've never seen it on the yoke but rather connected to the chassis or somewhere on the CRT mounting system.

My dumont RA 103 doghouse had a loop on the yoke/yoke support...My 17" predicta had a single grounded wire that was riveted to the back of the yoke bent over the side and stuck out past the front of the yoke such that it touched the dag....Not the most common practice, but I've seen it more than once.

Montman 02-11-2018 09:17 PM

Electronic M: the aquadag around the picture tube ground loops off the yoke mount has chipped off. That is probably the issue of arcing around the yoke ... so thanks!

Would anyone know what I can paint or apply on the glass area around the missing aquadag to complete the ground?

Or is it best to just more the loop?

Electronic M 02-11-2018 09:59 PM

A product called 'slip plate' works (there are other products too). To apply it remove CRT from TV, mask off places the dag should not be, feel for loose patches of the original dag and knock loose patches off, spray new coating on over glass and solid parts of original dag making a reasonably thick complete coating, allow to partially dry (to where it won't run), remove masking, allow to finish drying.

Assuming the dag has not formed islands you can temporarily ground the dag by placing a spring or wire against a good part of the dag and connecting that wire to ground.

If the dag is not connected to ground somewhere then the outer dag can float to several thousand volts potential relative to the chassis...Once it floats high enough it will arc to ground at anyplace where it can....If you ground it somewhere decent it will be at ground potential and not arc......Now if there are dag islands all of them need to be grounded or they will arc to each other and or chassis (thus why you don't want islands: too much of a pain to ground multiple things).

Montman 02-17-2018 12:23 PM

just good the product and applied it. Will let you know if the arcing stopped. There was no aquadag under the grounding loops. Thanks.


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