FIRE! 1961 Zenith

[dieseljeep]

Originally Posted by andy

The insulation was probably cracking and damaged right where it goes into the interlock plug. I've thrown out several cords because they had copper showing at one end due to the extra stress on the insulation.

I found some of my cords are getting brittle after 40 some years. I have several pieces, Ive had that long or longer.
BTW, the cords on the equipment, sold today, are inpossibly stiff. I understand they're removing the plastisizer, as it's lead based.

[Zenith26kc20]

Did the cord have the famous "green goo" forming and bleeding around the plug and interlock? I've never seen a cord flame out from the goo but I have seen them sparking very slightly and it looks like interference on the picture. I clean them but it comes back eventually. I have soldered cords to the back of the pins on some to be on the safe side.
As for the vertical, it may be a resistor opened or went way up in value. My RCA KCS166 did that and I finally couldn't adjust the height anymore. Once I changed three resistors it was fine again!

[Jeffhs]

The interlocked AC power cord has another purpose besides protection from hot tube burns. Its primary purpose is to disconnect AC power from the TV when the back is removed so that the user will not get shocked from B+, or, worse, the 2nd anode voltage on the CRT.

These interlocks are not supposed to be defeated; if they are, of course, the safety feature is instantly lost, and anyone working on the TV will be doing so at their own risk. "Cheater" cords were used in the days of tube-type TVs to allow technicians to operate the set for testing purposes, although some TVs were used for years or decades (!) with cheater cords when the set's interlock cord frayed at the end that plugged into the interlock pins on the chassis. The TV may have worked with this lashup, but the safety feature of the interlock was destroyed immediately.

I would not recommend bypassing the AC interlock for any reason. These were installed on TVs and even some AC-DC radios for a reason: to prevent electric shock. There is almost always a warning on the back covers of 1950s-'60s AC-DC radios and, of course, televisions, stating that the interlock must not be defeated. To service the tubes, remove the back cover completely; do not try to service the set with the back on. I mention this because I'm sure some folks may have tried this; i. e. they would take the screws out of the top of the back cover, leaving the bottom and/or side ones in, and try to replace bad tubes while the unit was still plugged into the wall socket and turned on. I don't know how many people were shocked or killed this way; however, I will say this is a mighty foolish way to repair any radio or TV.

BTW: One series of radios I can think of right now that did not have AC interlocks were the Zenith H511s (H511Y, G, W, et al) of the early 1950s. These sets were potential death traps due, at least in part, to the lack of an interlock power cord, and also because they were "hot chassis" devices, meaning one side of the AC line was connected directly to the chassis. I sometimes wonder if these sets were UL approved, or even if Underwriters' Labs was even in existence in the early '50s. If they were, I cannot see how these Zenith radios would pass inspection without an AC interlock.

[Jon A.]

I just aired and threw out a very weak A63, or 25V CRT with an old power cord tied to one of the mounting lugs in order to lower it into the dumpster to avoid a loud noise. Once the cord got the full weight of the CRT it was cut clean through. Still, far less noise than expected.

Defeating the interlock though is especially risky when there's a polarized plug involved. One wrong move could "liven up" a chassis that is normally connected to neutral.

[user181]

Originally Posted by Jeffhs

. I sometimes wonder if these sets were UL approved, or even if Underwriters' Labs was even in existence in the early '50s.

UL was founded in 1894.

[Dude111]

Originally Posted by Kamakiri

Just grab the power cord off your RCA. They should be the same. Wonder how the hell that could have happened?!?!?! It was fine when it left here.....unless it somehow got pinched in transport?

Gosh I feel terribnle this happend........... I hope she didnt get hurt!!!


I hope you can save her buddy

[Kamakiri]

I thought it might have been pinched in transport, but my friend Al, who did the transport, reminded me that I removed the cord prior to the move from Buffalo to Maryland.

[dieseljeep]

Originally Posted by Jeffhs

The interlocked AC power cord has another purpose besides protection from hot tube burns. Its primary purpose is to disconnect AC power from the TV when the back is removed so that the user will not get shocked from B+, or, worse, the 2nd anode voltage on the CRT.

These interlocks are not supposed to be defeated; if they are, of course, the safety feature is instantly lost, and anyone working on the TV will be doing so at their own risk. "Cheater" cords were used in the days of tube-type TVs to allow technicians to operate the set for testing purposes, although some TVs were used for years or decades (!) with cheater cords when the set's interlock cord frayed at the end that plugged into the interlock pins on the chassis. The TV may have worked with this lashup, but the safety feature of the interlock was destroyed immediately.

I would not recommend bypassing the AC interlock for any reason. These were installed on TVs and even some AC-DC radios for a reason: to prevent electric shock. There is almost always a warning on the back covers of 1950s-'60s AC-DC radios and, of course, televisions, stating that the interlock must not be defeated. To service the tubes, remove the back cover completely; do not try to service the set with the back on. I mention this because I'm sure some folks may have tried this; i. e. they would take the screws out of the top of the back cover, leaving the bottom and/or side ones in, and try to replace bad tubes while the unit was still plugged into the wall socket and turned on. I don't know how many people were shocked or killed this way; however, I will say this is a mighty foolish way to repair any radio or TV.

BTW: One series of radios I can think of right now that did not have AC interlocks were the Zenith H511s (H511Y, G, W, et al) of the early 1950s. These sets were potential death traps due, at least in part, to the lack of an interlock power cord, and also because they were "hot chassis" devices, meaning one side of the AC line was connected directly to the chassis. I sometimes wonder if these sets were UL approved, or even if Underwriters' Labs was even in existence in the early '50s. If they were, I cannot see how these Zenith radios would pass inspection without an AC interlock.

Your first statement was covered in an early entry.
All the warning language, stated on an electronic product, is to remove the liability of the manufacturer and to satisfy U/L requirements.
If someone disregards the warnings on the product and is injured or killed, they don't have a legal leg to stand on.
Regarding the Zenith H511 radio, if you look at the schematic, you'll see C-4, that is connected from B- to the chassis. Technically, it is not a hot-chassis design and can meet U/L standards.
Sixty years later, I'm sure that the cap is leaky and will pass more than the original designed voltage level.

[Coshi]

5v3 was going bad I replaced it and the screen got bigger. But the power serge managed to kill the refrigerator too.
still not up to where it was but still

[playdrv4me]

Originally Posted by Jeffhs

try to replace bad tubes while the unit was still plugged into the wall socket and turned on.

Perhaps I am missing something here, or does this not just speak to a complete lack of common sense and stupidity?

I'm not sure how this interlock thing works, but it would seem that anyone with half a wit about them should START with unplugging ANYTHING consumer related, or at least anything not operating AFTER an isolated external transformer at low voltage, from the WALL socket. I get that this interlock thing I guess was designed to be a secondary "gateway" required before the set could be opened or whatever, but I'd have to assume anyone browsing this forum has enough common sense not to need such a nanny device and unplug the thing that could potentially kill you before doing anything else.

I suppose you could be liable if you sell the TV on to someone else or someone inherits it after you bypassed it. Is that where the concern lies?

[DavGoodlin]

This cord failure may have been caused by the reduction in conductor strands due to most being broken. The remaining few strands have to carry 2 amps (18 gauge cords are usually rated for 7 amps) and likely acted like a fuse, heating up, opening and then arcing to cause that much damage.

The stress at the interlock cap is very high. The cords are pulled enough in its 53-year life to have been severly compromised. I have many sets with cords that look OK but some do have the green slime (copper oxide?) but I hate to remove an OEM part unless I notice obvious tension damage or exposed conductors.

With old radios, and I sell quite a few, its easy to replace the pigtail (non-interlock) and put on some appropriately colored 18/2 SPT cord with a vintage-looking plug, be it polarized or not. Otherwise, if Im feeling cheap, I liberate a polarized one from a derelict chinese appliance, which are never in short supply.

This "event" with the 1961 Zenith gives pause because it probably looked OK. Collectively, we would do good to find some NOS replacement interlock cords and replace them as a matter of course when selling a set. I would never wire one direct, bypassing the interlock device.

[dieseljeep]

Originally Posted by Coshi

5v3 was going bad I replaced it and the screen got bigger. But the power serge managed to kill the refrigerator too.
still not up to where it was but still
]

Some real wild occurances there! A defective power cord connection, caused all that.
Is the refrigerator on the same branch circuit as the TV?
Does the refer have the fancy control board in it? They're rather sensitive to surges and power dips.
The newer NEC, now requires arc-fault circuit breakers, that prevent the type fault, that occured. They are rather sensitive and sometimes they trip with a non-fault condition.
BTW, the set looks like it needs power supply electrolytics.

[Kamakiri]

The set had all new filters, unless running them at 137V and then this short caused something with them.

[bigaudioal]

This set has all new electrolytics, new by-pass caps and had been performing flawlessly for half a year.

The power cord was in perfect condition and transported NOT attached to the set. No visible damage to cord or plug socket.

Not sure what caused the cord to fry like that, but remember you ran it at 137 volts for some time. That may have done some damage.

[user181]

Why was the set run at 137VAC?