some basic questions after recap Emerson 637A

[CJVx]

After a recap of the paper and electrolytic caps, the power up was fairly uneventful.

Power up was fine, good vertical but poor horizontal stability. It will do the following:

At first when the screen comes up, it is out of sync. i can dial it in with the hold control, but it only stays for a few seconds, scrambles, syncs again, scrambles etc. It does this for about 5 minutes, then finally stabilizes and will hold sync, however the horizontal hold control is still rather touchy. I left it on for a few hours, dialed in the vert and horiz settings to get a full linear picture and everything remains stable. After cool down, and power up again, the pattern repeats.


The picture is rather dark, and will wash out with added brightness. The focus control will focus it to something usable, but it is not sharp by any means.

I did test all the tubes, and replaced any weak reading ones.

Any tips for looking into this horizontal thing and dark picture?

These might be common questions, but i tackle a TV every few years, and this is my third attempt, with one of them currently shelved pending further investigation.

[Electronic M]

Try subbing tubes. If that fails let it warm up to stable and hit every resistor in the stage 1 at a time with freeze spray or canned air and see it any cause it to act up, if not that try spraying the micas. Change the parts that make it act up when sprayed.

[CJVx]

Thanks, sounds like a plan with the freeze spray. I did already try tube subs, without any differences.

[Eric H]

Sounds like something is drifting in the oscillator or sync separator circuits, possibly a resistor. Freeze spray is good, but you can sometimes find bad resistors by heating them up with a soldering iron, don't cook them, just a bit of heat to see if they cause the sync to go crazy.
If the Sams has a Horizontal setup procedure do that first.

Did you test the picture tube? Dark washed out picture could be a bad CRT but could also be something else in the video circuit.
Did you adjust the Ion Trap on the CRT for maximum brightness?

[CJVx]

First off, i believe the extended warmup until things stabilize was either caused by one or two faulty connections from a large transformer mounted on the side of the chassis under the horizontal components. Now at a cold start, it is out of horizontal sync for 20 seconds or so after the picture appears on the screen.

Another conditions i just noticed is after following the horizontal sweep adjust procedure in SAMs for the series b through c, which should be similar are as follows.

First real adjustment is to adjust the horizontal drive maximum clockwise until there is not picture crowding. At maximum i don't see any crowding of the picture. Just a reflection line because of this next condition-The picture is wide, and will not shrink all the way down to where it should be even at the extent of the horizontal size adjustment coil.
What could cause this?


I still have a dark picture. I don't have a CRT tester so i couldn't test the picture tube.
I did adjust the ion trap magnet for the brightest picture. As found, It was preset as far back as it will go until stopped by the plug socket, and that seems to be the area where the picture is the brightest at the proper rotation. Not sure if i remember any other sets with it all the way back there.

[Yamamaya42]

"The picture is rather dark, and will wash out with added brightness."

you mean it's blooming?

do you have a high voltage probe?
Are you getting the correct amount of high voltage?

[CJVx]

Originally Posted by Yamamaya42

"The picture is rather dark, and will wash out with added brightness."

you mean it's blooming?

do you have a high voltage probe?
Are you getting the correct amount of high voltage?

Its blooming as i turn up the brightness, then it becomes all gray with some faint white curled lines.

I don't have an HV probe, what are thoughts on a high resistance divider circuit to measure?

[Electronic M]

You have several hundred meg resistors laying around?

[CJVx]

The highest resistors I've found around here is a bundle of 20 5.6 Meg and 20 3.3 Meg. I could in theory do something with those, but i'll probably just wait until i pick up the right tool to measure the HV.

well its back to doing the horizontal jitters, and now its not clearing up after 5 minutes. Here is a youtube link to the behavior and at the end of the clip i turn up the brightness to show the screen wash out.

https://youtu.be/RY4rpRSBtKs

[init4fun]

It looked to me like it was loosing both horizontal and vertical sync ?

[CJVx]

Originally Posted by init4fun

It looked to me like it was loosing both horizontal and vertical sync ?

I think the loss of vertical is a byproduct of the horizontal issue, I see it is rolling sometimes during the freak out, but I think its triggered by whatever is going on horizontally.

[Kevin Kuehn]

Have you verified your horizontal hold control has a good solid carbon track? For how fast that jumps in and out, it seems as if there's a intermittent connection. Or possibly a mica cap intermittently breaking down, or even a socket or cold solder joint? And in what condition is the dag on that CRT, that is if it's relied on as the only filter for high voltage. I think it's ability to self restore is a clue that's an intermittent contact point.

[Phil Nelson]

Originally Posted by CJVx

I did adjust the ion trap magnet for the brightest picture. As found, It was preset as far back as it will go until stopped by the plug socket, and that seems to be the area where the picture is the brightest at the proper rotation. Not sure if i remember any other sets with it all the way back there.

Is it possible that someone reversed the ion trap magnet? Sounds silly, but odd things can happen if a teenager gets his hands on Grandpa's old TV and is inspired to "fix" things.

Some ion trap magnets are marked with a little arrow, which should point toward the front of the CRT. Other magnets don't have an arrow, so don't freak if yours lacks one.

You won't hurt anything if you flip the magnet back to front and try sliding it forward and back on the CRT neck, and rotating, in the usual manner for finding the "sweet spot" with maximum brightness. If no improvement, put it back the way you found it and look for other causes.

Just an idea . . .

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

[Eric H]

Originally Posted by CJVx

well its back to doing the horizontal jitters, and now its not clearing up after 5 minutes. Here is a youtube link to the behavior and at the end of the clip i turn up the brightness to show the screen wash out.

The jitters look like it could have a bad Mica cap in the Horizontal.

As for washing out it may just be you're turning up the brightness too far since it looks okay otherwise, the white lines are retrace lines, often caused by running the brightness too high, though a weak CRT can aggravate the problem.

I don't see any blooming, blooming is when the entire picture gets larger and dimmer as you turn up the brightness, often caused by a bad HV rectifier tube, your raster stays the same size even with the brightness cranked up, that's generally a sign of a healthy high voltage supply.

[CJVx]

Originally Posted by Phil Nelson

Is it possible that someone reversed the ion trap magnet? Sounds silly, but odd things can happen if a teenager gets his hands on Grandpa's old TV and is inspired to "fix" things.

Some ion trap magnets are marked with a little arrow, which should point toward the front of the CRT. Other magnets don't have an arrow, so don't freak if yours lacks one.

You won't hurt anything if you flip the magnet back to front and try sliding it forward and back on the CRT neck, and rotating, in the usual manner for finding the "sweet spot" with maximum brightness. If no improvement, put it back the way you found it and look for other causes.

Just an idea . . .

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

Phil, you were onto something , I flipped it around and it’s in a position midway on the neck now, although I did not gain any brightness in the sweet spot of the new position.

Also I changed out all the mica caps in the horizontal circuit, still jitters.

The dag is actually in pretty good shape and the contacts by the yoke are making an electrical connection.

I am thinking maybe there is a bad connection at the yoke...for the reason that i *think* I am getting changes when I tap on the yoke and or pull on the wires. No changes when I poke and spray anything under the chassis. The only changes I might be perceiving are if I flex the chassis when it’s running.