Zenith porthole chassis removal?

[mbates14]

Working on my tabletop zenith porthole, but I cannot figure out how to remove the chassis. the top of the CRT wont clear the back of the cabinet as far as I can see.

Thoughts?

[old_coot88]

Probably hafta tip the whole chassis+CRT forward as you pull it out(?).

[mbates14]

Yeah, I got it.

I think the flyback is toast though. It does not look too good, but the .25A fuse isnt blown.

[Eric H]

You just tip the chassis forward when the CRT gets to the back edge.

I replaced the Flyback in my Zenith Mayflower Porthole with one from an early RCA 630 chassis.

[mbates14]

Yeah, I got it. That's what I ended up having to do.

Surprisingly, the flyback is actually good. I resealed it with some Corona dope red insulating varnish.

Trouble is when drying the chassis after cleaning it. I got the channel knob too hot so it's been ruined.

[mbates14]

I got her running at least. Still waiting on a few parts to come in to try and finish it.

The "mica" caps in here are all shot too, i had to change one. Need to change the rest as its acting like it has "silver mica disease" in the picture sometimes. Also sometimes the horizontal sync will go byebye and itll start smoking the 120K resistor in the horizontal control plate load. I have to quickly power cycle the set and its fine.

Then, the 3300ohm 5W resistor in the audio plate path is running about 5.6 to 6W so it gets too hot, tube is otherwise functioning normal so i think its mis-speccd in the service manual. Likely gotta bump that to 10W.

I also seem to have a lack of contrast as well, I have to bump it all the way. plus, the raster blooms when the brightness is cranked, HV falls to 8KV from 11KV. so possibly the 1B3 is weak as well.

[Electronic M]

Wire wound power resistors typically run very hot at their specified wattage. Typically that's fine...The resistance doesn't change unless you get close to melting the wire so as long as there's enough head room between operating temp and melting point they can run hot enough to cook meat all day.

It's when a resistor starts smoking that something is wrong (or there's some substance that landed on it cooking off).

[mbates14]

Sure, and I get that.

In this case, i performed the ohms law calculations based on resistance and voltage drop, sure enough that 5W resistor is dissipating closer to 6W so im a bit uncomfy. I decided to order up a 10W and we will use that. Stil going to get hot, but itll be within the acceptable limits of the resistor.

Anyways, I still have weird issue that ive not been able to nail down. Its acting like theres "silver mica disease" in the picture, causing white flashing lines to come and go, as well as the vertical to get jumpy. so i need to figure that cause.

there was an issue with the horizontal sync coming and going especially tapping the chassis, there is a 4 pin plug on the chassis that has a bypass thingy in it. That was all dirty so i contact cleaned that, solved my horiz sync issue.

Now, the vertical sync and picture noise that comes and goes. all the tube sockets are clean and dont make noise when wiggled. so its an electrical problem.

I tried spraying the resistors and things with freeze spray to see if i can get it o act out.

But since I already had one leaky mica cap (2Megs in one direction, 8 megs in another) i bet the rest are bad too.

[Electronic M]

I worry if measured power in a resistor is exceeding the power rating. Engineers don't spec resistors of lower power than they designed the set to send through those resistors...So somewhere something is wrong and overloading that resistor.

Are those white lines in short dashes in a 3x3 grid? If so and you are using a DVD/Blu-ray player or a VCR then those are not the set's fault, but rather a form of analog copy protection called macrovision encoded on the media your playing. Macrovision violates NTSC signal standards and messes with TVs that predate VHS...TVs made after VHS came out have design tricks to suppress those lines.

[mbates14]

Originally Posted by Electronic M

I worry if measured power in a resistor is exceeding the power rating. Engineers don't spec resistors of lower power than they designed the set to send through those resistors...So somewhere something is wrong and overloading that resistor.

Are those white lines in short dashes in a 3x3 grid? If so and you are using a DVD/Blu-ray player or a VCR then those are not the set's fault, but rather a form of analog copy protection called macrovision encoded on the media your playing. Macrovision violates NTSC signal standards and messes with TVs that predate VHS...TVs made after VHS came out have design tricks to suppress those lines.

Only thing that resistor feeds is the audio circuit. voltages in that circuit are ok, but the tube is biased around 35ma when the datasheet says somewhere around 25ma.

Also no, its not a "retrace line" scenario. its hard to describe. its like noise from a bad/intermittent connection or silver-mica disease.

[mbates14]

Here is the issue i keep running into:

https://youtu.be/fKDK8PTT8lA

[zeno]

Looks like video is dropping out. If the audio is OK I would look
at the video after the SND take off point. Check the CRT pins also for
bad solder. This is a great place for an analyst & scope.
On the resister watch for 'lytic caps on either end. If one opens
the other takes over & heats things up. Seen that a few times on RCA tin can
19" colors. You could also pull the audio out, if in // filaments to see if things
cool down.

73 Zeno
LFOD !

[mbates14]

Originally Posted by zeno

Looks like video is dropping out. If the audio is OK I would look
at the video after the SND take off point. Check the CRT pins also for
bad solder. This is a great place for an analyst & scope.
On the resister watch for 'lytic caps on either end. If one opens
the other takes over & heats things up. Seen that a few times on RCA tin can
19" colors. You could also pull the audio out, if in // filaments to see if things
cool down.

73 Zeno
LFOD !

Getting in there with an insulated tool, jabbing and bumping around under the chassis does not change the behavior.

I also tried the heat gun/freeze spray approach on various components through the stages, and its not really making a difference.

it has me stumped honestly. Sound I dont know until i get the higher wattage resistor in, so the audio out tube is pulled.

I think the dropout is before it seperates off for the sync, since we can see its affecting the sync as well.

[mbates14]

Also the sams i got for this thing, does not cover this chassis at all even though it mentions it on the front that it does. Schematic is totally wrong as well, as i think its setup for the split chassis 16" version