Hot FLY on Magnavox CTC12 clone tv

[Tony V]

Since the subject has been brought up about hot flybacks in color tv's, i thought i would ask about my Magnavox CTC12 clone that i have without hijacking the other thread.

The flyback in mine gets hot also but mainly at the core which gets really hot to the touch after a couple of hours of playtime. Is this normal? The "doughnut" itself only gets warm and not soft but there has been some minor drippage that seems to have come from the center.

The flyback is a NOS replacement with less than 20 hours on it. The efficiency coil has been properly adjusted, the sweep and rectifier tubes replaced, and the hv has been adjusted but can only get 21kv out of it. There is no blooming, the picture is nice and sharp and it plays perfectly. The only thing besides the heat problem and the slightly low hv, is the filament of the hv rect tube seems a little bright to me. It was always my thought that the filament should only be seen in a dark room.

Any feedback you all could give me on these questions will surely be appreciated as i dont want to ruin the new flyback.

Thanks!

[JohnCT]

Originally Posted by Tony V

Since the subject has been brought up about hot flybacks in color tv's, i thought i would ask about my Magnavox CTC12 clone that i have without hijacking the other thread.

The flyback in mine gets hot also but mainly at the core which gets really hot to the touch after a couple of hours of playtime. Is this normal? The "doughnut" itself only gets warm and not soft but there has been some minor drippage that seems to have come from the center.

The flyback is a NOS replacement with less than 20 hours on it. The efficiency coil has been properly adjusted, the sweep and rectifier tubes replaced, and the hv has been adjusted but can only get 21kv out of it. There is no blooming, the picture is nice and sharp and it plays perfectly. The only thing besides the heat problem and the slightly low hv, is the filament of the hv rect tube seems a little bright to me. It was always my thought that the filament should only be seen in a dark room.

Any feedback you all could give me on these questions will surely be appreciated as i dont want to ruin the new flyback.

Thanks!

Any chance you overlooked a cracked core before installing it?

John

[Tony V]

It was just installed before i bought the tv so i have no idea about that.

[JohnCT]

Originally Posted by Tony V

It was just installed before i bought the tv so i have no idea about that.

I put in maybe a thousand HV flybacks in color TVs over the years, but confess to never having used my finger thermometer to test core temperatures after several hours of running, so I don't even know what's normal.

If you have an IR thermometer, take a core temperature and hopefully someone here with a similar chassis can do the same for you for comparison purposes. For all we know, your TV may be normal.

If you think this is something that might affect the long term surviveability, you can remove the fly and see if it does have a cracked core. If the core is cracked *and displaced* even a small bit, it will have eddy losses.

I've repaired late model SMPS transformers with cracked cores by getting the two sections to fit perfectly, and sealing with a FRESH tube of cyanoacrylate adhesive. The cyano won't add any gap whatsoever, but will soak into the ferrite and bond the two sections. Make sure NOT to use the gel type. You want the low viscosity cyano to bond ferrite, ceramic, and other porous hard materials.

If you can get the two pieces to fit perfectly and bond it perfectly, the difference in performance will be virtually indistinguishable from a non cracked one.

Also, what you are experiencing may be normal although disconcerting. I've seen ferrite core transformers have heatsinks strapped to the core.

Maybe adding a heatsink if there's room enough and even a very small, very slow CCF fan will improve the situation to where you won't get wax loss at the core. You would be amazed at low a fan speed you need to drop the temperature of a part contained in an enclosed area.

John

[Tom9589]

With only 21 KV maximum, I wonder if the HV regulator is loading down the system and putting excessive load on the flyback. I'd disconnect the cap on the 6BK4 and see what happens to the HV. If it shoots way up, you need to troubleshoot the HV regulator circuit. Be sure and only run the set for a short time with the 6BK4 cap removed.

[timmy]

Cathode currant ?

[bluenorm]

is your high voltage probe ok?

[Electronic M]

Another thing that may help to cool the core is to apply thermal paste between it and the chassis (and any metal flyback frame that might exist between the two...if you can use the chassis as a heat sink it's a reliable passive cooler.

[Tony V]

Thanks for the suggestions so far. I will investigate further and give you some feedback soon.

[doogie812]

Cracked core would be my best guess but don't rule out cathode current (leaky control grid coupling cap) leaky 3A3 or 6BK4. Bad cap in the boost circuit as well. I have seen many flybacks smoked from leaky HV rectifiers.