Degaussing a CRT is a kind of magic

[intric8]

A couple of weeks ago an elderly woman in the Seattle area contacted me. She had some old Commodore hardware that her daughters used in the 1980s and wondered if I wanted it.

Rather than it go to the e-cycling center, I thanked her for reaching out and met her a few days later in the parking lot of my office. I transferred a few things from the trunk of her car to mine, we spoke for a couple of minutes and she was on her way.

Back in the 1980s her girls had been given a Commodore 64, a 1541 disk drive and a monitor by their uncle. He'd used it all for a while then gave the setup to them. According to the lady, her daughters "never really got into it" and ultimately the things were put into storage. For decades.

The things I was given, besides being dirty and a little sticky, were in fantastic condition. Or so it seemed. This past weekend I finally got around to testing the 1702 monitor.

I was disappointed to see this image:

"Could be a bad flyback, or maybe bad capacitors."

To be honest, I was a little surprised I got an image at all if the monitor hadn't been powered on for almost forty years. And no immediate white smoke is always a good thing, too.

While photographing a CRT isn't exactly easy or always representative of what we see in-person, this photo is pretty close. If anything the washed out area in the center and right side of the screen was even worse. It was much brighter than what I could capture with my camera. In other words, it wasn't good. The text at the top of the screen was also rather fuzzy, and all of the colors were off.

I reached out to a friend of mine who recommended I try a cheap degaussing wand before sending the 1702 out to pasture. They only cost $15 and AMZN offered next-day free shipping. I figured it was a cheap gamble so I placed the order. This is the one I got.

Then I watched a few short videos on YouTube on how to use the thing. Seemed simple enough. Point the thing at the monitor and wave it in a somewhat circular motion while slowly moving away from the screen.

As advertised I got the wand today one day later.

I moved the 1702 to the center of the room (away from my other CRTs) and gave it a try. Pretty trippy color blobs appeared on the screen, but after three tries the washed out areas on the CRT remained. "Was the center mostly clear now?" I tried a fourth time, this time focusing more on the affected areas and kind of willing the blobs to the right edge of the screen and "wiping them away" in a somewhat exaggerated horizontal motion. "Shoo, fly!"

And then...

[Zippy Zapp]

Glad you got it sorted out. The 1702 is an excellent monitor for C64 goodness.

One thing I do appreciate about more recent monitors, like most Sony Trinitron computer monitors is a degaussing function built-in.

My limited (very limited) understanding is that the 1702 does have a degaussing coil that is supposed to maintain the CRT picture purity. The part number is (JVC) A39477-T. Which makes me wonder: Does this coil actually work or can it go bad? Perhaps the circuit it connects to is having an issue?

Or could the years in storage perhaps near some sort of magnetic field be too much for the built-in coil?

More of a curiosity as I don't hear the loud thunk with a 1702 when it powers on like I do with a Trinitron Computer monitor as it degausses the screen.

[morten.dynamite]

The degaussing circuit in older CRT (Monitors and TVs) usually is very simple a dual PTC resistor in one package one PTC in series with the degaussing coil and the other PTC across the mains to keep the PTC for the coil warm so the degaussing is off an only activated on cold starr, and they can go bad.

I am an old Radio and TV repair man so I have replaced numerous PTC modules on TVs and monitors.

Some later models TV hade triacs or relays to control the coil so it could be activated even when the TV was started from standby (warm start).

[Zippy Zapp]

The degaussing circuit in older CRT (Monitors and TVs) usually is very simple a dual PTC resistor in one package one PTC in series with the degaussing coil and the other PTC across the mains to keep the PTC for the coil warm so the degaussing is off an only activated on cold starr, and they can go bad.

Thank you for the information!

I am an old Radio and TV repair man so I have replaced numerous PTC modules on TVs and monitors.

That is great. As retro people many of us are not so savvy with repairs on this equipment. Good to know there is someone with some knowledge around. Do you still repair TVs now?

Some later models TV hade triacs or relays to control the coil so it could be activated even when the TV was started from standby (warm start).

Gotcha. My Sony's must use these methods since it has a dedicated degaussing function in the menus.

[morten.dynamite]

It happens I do some minor repair for people I know and I do some projects for myself but I have some chronic pain issus because nerv problems in the neck shoulder region so my right arm get numb and week when I use it.