Zenith H2438R "Aldrich" restoration

[timmy]

Originally Posted by bandersen

It should lower the needle, not raise it during the cutoff test.

Not sure what you mean by truthful. Don't think I've ever found a 7JP4 with bad emissions - it's the phosphor that wear out first. Probably why Sencore dropped the 7JP4 from the tube chart in later versions.

The needle went up alittle bit in emission test the cutoff don’t work with these tubes being the 440 was not made to check the 7jp4.

[Yamamaya42]

Speaking of caps, if I remember correctly, a new style 0.047uF film type should be OK to replace a old paper 0.05, as the .05s are so hard to get, and the 0.047uF are all over the place, and a a good price.

[bandersen]

Of course, they differ by less than 10%. Anyway, there are no 0.05 caps in my set ��

[bandersen]

Finished replacing the paper caps and open power resistors last night and fired it up.


It produces a raster, hiss out of speaker and the tuner is creating some snow. Can't display a test pattern though.


After running a few minutes, the main filter cap was getting quite hot so I shut it down before it vented. Another twist lock on the main chassis was also getting warm. I'll tackle those next.


Also starting some cabinet work. There's masking tape reside on the control panel and screen bezel I need to remove.

[bandersen]

Kinda reminds me of the Crosley 9-407.

Here's a peek inside the big tuner drum. Each strip has caps and coils for a single channel. I believe they claim its UHF ready meaning the tuner LO can handle the higher frequencies. Just pop in some UHF strips for your broadcast area. LO uses a 6C4 oscillator.

I am able to sort of pick up a signal as I rotate through the channels. I can hear and FM radio station and briefly see my test image. I thought it might be dirty contacts, but some testing revealed bad tubes including a 6CB6 in the tune with no emissions.
Also found a weak 6AU6 IF tube, 12AT7 and 17AU7 AGC and video amp
I'll pop in some replacements shortly.


Replacing some electrolytics also increased the vertical deflection. Have not been shocked...yet...

[bandersen]

Replacing the tubes didn't help much so I tried signal injection. Here's I'm injecting composite video directly into the grid of the first video amp.

While hooking it up I noticed I missed the 0.047uF coupling cap to that grid. I expect replacing it will improve the things.

Injecting with that cap in place, I do get an image but vertical height, linearity and hold are all terrible.
I expect replacing the electrolytics in the vertical circuit will help with all that.

[bandersen]

Here's one of the channel sections.


I dug deeper into the tuner to lubricate the fine tuning shaft.


Hmm, that's doesn't look right.


I think it was a 1.5K resistor but Sams only shows 1/2 watt resistors in the tuner. I'll trace out the wiring to confirm.

[Yamamaya42]

Ha!
I KNOW WHAT IS ON THAT TV IN THE BACKGROUND!

https://www.scifihistory.net/uploads...52023_orig.jpg

Season 1 episode 1, Breakaway!

[bandersen]

LOL, I figured someone would

[bandersen]

This set will be going back on the bench soon. Replacing that crispy resistor did not get me great reception so more work to do.

Also, our local radio club recently contacted me about some TV chassis found in a collectors estate they were helping clear out. Luck would have it one of them is the same (or very similar) as my set so I have a source of spare parts if needed.


There is also a little bonus. This set has the "lazy bones" remote channel changer option!
It consists of a small power transformer, motor + capacitor, latching relay and some gears.


Very easy to unmount and transplant.


Assuming it works, that leaves one challenge - I don't have the handheld remote��
It would have fit into this cradle that mounts on the outside of the cabinet.


So I'm on a quest to find one...