Is there a trick to setting purity?
 

I went about setting the purity on the Avanti set today. I was told to orient the set east to west when doing so (CRT screen facing west and yoke facing east). I followed all instructions, but could not get a red dot on the screen. The best I could get was about 70% of screen coverage and no smaller. I went about adjusting the rings and managed to get the center of the screen pretty red and then I just forward the yoke. As I moved it, the red didn't stay pure. A little more tinkering and I finally got the entire screen red and locked the yoke back down.

Well I moved the set 90 degrees and now the on screen colors vary across the screen. Some areas a little more red, some a little more green, etc. I'm assuming this is because of the magnetic field? If so, what do I need to do to adjust the purity so it doesn't change as I move the set around? I'm sure it's possible because no other set I have changes.

Hmmm....

Thanks

You need a Degaussing Coil, sets of that vintage often needed degaussed whenever they were moved.
http://www.ebay.com/itm/9317-GC-DEGA...item3a82bccfd1

It should have one built in but it may not be powerful enough to degauss a badly magnetized tube.

I would set the purity after degaussing and in the orientation that you intend to use the set in and not by compass points, usually once it's set you can just degauss it when you move it and it'll be OK.

You don't have to get a red dot, just get as much of the screen as possible red and as centered as possible, then slide the yoke forward until the entire thing is red.

My brother has a degaussing coil, but I won't be able to get my hands on it until next Friday.

Do you know of any way to test the degauss function? How do I know it's working properly? It's a '74 Zenith CC2 Avanti w/25EC58 chassis.

Thanks

Usually you can hear a very short 60 cycle hum coming from the CRT area on a cold start if it's working, not always though.

Well did some testing today. The degauss circuit shows 120V when the coil is disconnected. With it connected, it shows less than a volt. I went over the schematics and I found a thermistor that I believe is the culprit. I looked up the part number and got 63-8687. Doing an internet search got me to a few sites selling the replacement part of ZEN63-10710. I'm trying to find a place local to Hollywood, CA as the part 4.80 and the shipping is another 6.00. Kind of pricey.

Stay away from eBay - the same thermistor (a workman equivalent) is $24.95 But shipping is FREE.....:D

Encompass (formerly TriTronics) had my degauss thermistor about a year ago for 7 dollars, plus shipping, don't recall how much, but UPS is expensive these days. Mind you, Encompass is the worst for shipping time -about four days after ordering, they notified me it was being shipped. I figured I was a small fish compared to the repair shops buying their projection lamps and HDTV boards.

Cheers,

I just ordered it from the same place I order the OEM Zenith safety caps (Talon Electronics). Was 4.60 for the thermistor and 4.80 shipping. They were very fast at turnaround last time, so I don't mind spending a little more for shipping. I had the last ones in three days. They just sent me a shipping number, so I'm assuming it will be in the mail tomorrow and I'll have it by Wed.

I stay away from ebay for parts. I once order some capacitors and the +/- was way higher than the one pictured. It was a complete waste of time.

This is normal behavior for the degauss circuit , and is not an indication of trouble . When stone cold , the thermistor passes all of the power , as it has a low resistance . When the circuit is energized , and the coil draws massive power through the thermistor , it takes less than 1/2 second for it to go from passing the power to it's warm state where it becomes a very high resistance and passes no power . The action of the degauss coil thereby is SO brief that it's almost impossible to catch on a voltmeter , full voltage for less than 1/2 a second then essentially "open circuit " .

If the degauss coil WERE to be operating while there was a picture on the screen the picture would be badly distorted for the duration of the coil's on time . Since it happens for such a short time on initial power up , before the screen has begun to show light , the slight brief "60 cycle sound" that was mentioned by Eric and a properly colored picture are the only real ways to tell if the circuit has in fact done it's job and demagnitized the screen .

:thmbsp: Best of Luck with it .

The 63-10710 was THE DGS thermistor for years in Zeniths.
We got them 25 at a time & they also went in many other sets.
No harm in changing it, they always fall apart when old anyways.
As far as purity goes if you move the set much & turn it back on HOT
it will often be off. You DO NOT have to re do it because you
moved it. Just a manual DGS at most, the set will clear itself after a few cold starts anyhows........

73 Zeno:smoke:

The thing is, is that I have restarted it more than 10 times after letting cool for an hour, two hours and over night. The colors are still messed up over the screen. Also, I put a compass right next to the actual coil and turned on the set. The needle barely twitched and there's no hum or other buzz type noise on startup.

It can't hurt to change it, though.