1966 Magnavox combo issue

[freakaftr8]

Hey guys,
Happy new year to all!

Im still having an issue with my Maggie combo with the horiz fluttering upon warmup.

I think I might have found the issue, it's in the horiz effiency coil. Has anyone ever seen this before? The coil actually has 2 parts to it. One coil on top of another with about a half inch between them on the rod. I was also told that adjusting this coil will fix the horiz width. Well it doesn't. The width is stretched and if I apply heat to the coil, it seems to make the screen flutter. This coil is really close to the Horiz osc tube also. Can this coil change resistance with heat?

Thanks!
Shawn

[blue_lateral]

I don't have the service lit for that set here, but generally speaking, a horizontal efficiency coil is not used to adjust width. It is, on most sets, a fairly critical adjustment used to tune the horizontal output circuit to resonance.

If we are indeed talking about the same thing, the main things affected are the horizontal output tube and the flyback, both of which are likely to get destroyed quickly if this is set wrong. Generally speaking, they tune like transmitters. If you are very far off resonance, the tube and plate tank (in this case the horiz. output and the flyback) will draw way too much current.

If you have changed that coil setting, I would read up on the procedure before you turn it on again. It should be in the Sams. Generally speaking, this will involve checking the horizontal output current while tuning that coil, and checking the 6bk4 current while setting the "HV adjust". The procedure most likely has to be done more than once, until everything looks ok at the same time.

I have no idea why the screen flutters when you heat the coil. I would be suspicious some other component or maybe a solder joint in the immediate vicinity.

John

[radotvguy]

being i have fooled with many magnavoxs, i can give you some advise . Check all solder joints, they seem to be a issue with older magnavoxs .

[freakaftr8]

If I have a possible leaky phase detector diode, (im assuming this is the diode set that is encased in a black plastic looking box with the 3 terminals coming out the bottom) could this drift when it warms up...

[freakaftr8]

Does anyone know of the values of the horiz phase detector diodes? And where can I get a new one?
Thanks..

[jpdylon]

You can use two 2n4004 diodes and make one. Just note where the cathodes are on the old device and solder the two diodes in place of it. It's worked well for me in the past.

On a rare occasion you may need to touch up the phase detector slug, but its rare...

[Bill R]

There are NTE/ECG subs for those.

[freakaftr8]

I went to Fry's last night, I picked up a bunch of Zener Diodes NTE, what should I use, I already tried some 2.7 volt 1 watt, and I have absolutly no stabilization I can stabilize it but a touch on the dial either way it comes out of lock, and the longer the set is on, it drifts, I picked up some 8.3v 1 watt and some 27v 5 watt diodes too, would these work? Mabye the problem wasnt the diodes at all... I bought some freeze spray, and had no effect on any of the conponents on the horiz osc board..

[andy]

You don't want to use zeners for this. Use a pair of small, low power diodes. Just about anything should work as they won't see much voltage, or current (do you have any junk electronics around). High power diodes might be too slow, or have too much capacitance for this application and zeners certainly won't work.

How do the original diodes test? The few times I've seen this problem, one or both of the diodes failed a simple resistance test with a VOM.

[freakaftr8]

They seem to have failed the test on one side.. Thanks for that info, when it comes to diodes im stupid.. Ill pick some up tonight !

[jpdylon]

Yes, stay away from zeners as Andy stated. They are meant to regulate voltage and do not do well as HO phase diodes

Once you get the diodes in, the erratic ho drifting problem should go away. I had the same problem with a few sets that used the dual diode-pack phase detector

[freakaftr8]

Well I replaced the diodes. I have horiz lock again, but still doing the same thing.. After 10 minutes of operation, sometimes sooner than that, the screen seems to start squiggling back and forth, then eventually looses lock, then I have to adjust for it. Then looses it again as it goes back to where the dial was origianally. This is wierd!!

[freakaftr8]

BTW, the interesting thing is that images that have rapid movement and colorful seem to affect the horiz squiggling and loss of sync faster and more erratically than images that are not moving, (like a dvd that is paused) then it just squiggles and doesn't seem to lose sync, but just squiggles back and forth. Oh when I say looses sync, it just looses enough to tear the pic, but it's not like way off or anything, just barely enough to tear the picture.

[jpdylon]

If this set uses circuit boards, you may have a solder joint failing or a trace that is breaking loose. I would focus your attention to the horizontal AFC and oscillator sections. Re-solder the tube sockets to be on the safe side.

Using a very well insulated stick (piece of wood or PVC) press on the board a bit. Note if the condition worsens or gets better.

If that does not help, check voltages on the horizontal afc tube to see if they are fluctuating when the symptom occurs. YOu may have a film cap that is trying to turn into a resistor.

[Bill R]

The Magnavox part number for the afxc diodes is 50093-1 This crosses to an NTE 178MP . That is a matched pair of 50v silicone diodes.

Bill R