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 Post subject: weird symptom
PostPosted: Feb Tue 06, 2018 12:56 am 
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Joined: Feb Mon 20, 2017 8:12 pm
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I have a Zenith radio Ch. 6Z05. Periodically the volume drops suddenly. If I flip a light switch on and off in the same circuit the radio is plugged in, the sound comes back up. May do this a couple of times and then be fine. Can anyone explain how this happens? At first,I would flip the phono/radio switch in the back and it would come back up. But then quite by chance I flipped on a light and discovered that also worked. Mark


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 Post subject: Re: weird symptom
PostPosted: Feb Tue 06, 2018 2:17 am 
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Location: Mountains of Mourne. Ireland.
Hi Mark,

SOP (standard operating procedure) is to replace all the electrolytic and paper capacitors as a first step. Resistors can fail open or short, alongside their value changing.
A good close visual inspection can often reveal circuit troubles and suspect components.
For suspect dry joints, touch them up (reflow) with your soldering iron.

Clean tube pins (lightly scrape with a sharp X-Acto knife) also check the sockets.

If symptoms still persist, consider this.
Watch: Replacing mica capacitors in an AA5 I.F. transformer.
viewtopic.php?p=2765766#p2765766

Service data kindly provided by Bill J.
viewtopic.php?p=2287121#p2287121


Greg.

oh... regarding the light switch... one of your components (is faulty... :shock: ) or its connection is
ridin'-on-the-edge...
I have an unrestored mid 70's transistor radio that does the same. Lol


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 Post subject: Re: weird symptom
PostPosted: Feb Fri 09, 2018 9:27 pm 
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Greg: I don't usually replace all of the paper caps, but did this time. Checked for poor/loose connections on the tube pins, and the radio is performing great. Volume is improved and no more dropping out randomly. Very good reception on this radio. It was my grandfather's and I remembering seeing it at their cottage as a very small child. Glad to have it in good working order. Mark from Kalamazoo


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 Post subject: Re: weird symptom
PostPosted: Feb Fri 09, 2018 10:30 pm 
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MarkinK-zoo wrote:
I don't usually replace all of the paper caps...

Then you need to start doing so.

They're bad, and will not heal themselves.

- Leigh

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http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: weird symptom
PostPosted: Feb Sat 10, 2018 12:00 am 
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While having as noted, Wax paper caps in it and perhaps dud resistors, is not helpful; If it is a component, other than a tube or mechanical issue? I commonly find that fault to be a Mica Cap. Generalising: If it goes off frequency its around the mixer, otherwise its likely to be on the AGC.

Marc


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 Post subject: Re: weird symptom
PostPosted: Feb Sat 10, 2018 12:50 am 
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Hey mark,
that's pretty neat that you still have your grandfather's radio... and it works too!


Paper capacitors, their makeup and how they age/fail.
A posting by Chris108... :)

See paragraph five...
"The other kind of capacitor to look out for is the paper type. These come in several shapes and sizes.
The problem with them is the paper inside. Paper is made of"...

http://www.antiqueradios.com/forums/vie ... 9#p2541899

Greg.


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 Post subject: Re: weird symptom
PostPosted: Feb Sat 10, 2018 2:00 am 
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Location: Long Island
Radios and other electronic devices depend on a lot of connections to work. Not just the ones you see where components are soldered to terminals or to circuit boards, but connections inside the parts between the leads and the active elements. If any of those connections is faulty, you could have a situation where the circuit works intermittently. When you consider the opportunities for poor connections between junctions of dissimilar metals, "tin whiskers" and crystallization, soldered joints, contraction and expansion due to temperature changes, oxidation of contacts in plugs, sockets, tube pins, switches, and controls, or shock and vibration as things are handled and moved from place to place, it's a wonder any of this stuff ever worked at all--let alone that it still works 60, 70 or more years after it was manufactured.

Anyway, when a connection is faulty, it is possible that it will fall into a high resistance, perhaps semi-conducting state. Or it is possible that a conductive path will develop between two terminals where it is not supposed to exist. If there is even a small surge in the voltages in the equipment, such as may result from moving a control to a different function or turning on a nearby light switch, it can break down the high resistance or semi-conducting film temporarily, then the circuit will work normally for a while. But whether the surge makes a bad connection more conductive or breaks an unintentional one, the fault will eventually re-establish itself and the circuit will malfunction again. Such problems can be very difficult to find since the simple act of taking voltage or signal readings can cause minor surges and make the problem stop. This was the bane of radio and TV repair shops because sets with intermittent conditions could play fine for weeks in the shop, but as soon as the customer took them home, the problems would come back.

Yes it is possible that your problem was due to a defective cap and it's now fixed. Capacitors absolutely can and do become intermittent, among their other failure modes. But it also could have been a solder joint, or maybe something non-related that got jarred or wiggled and is now making good contact again. If the radio works and the problem doesn't come back, good deal. But if it does, be patient and keep hunting.

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Thomas A. Edison


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 Post subject: Re: weird symptom
PostPosted: Feb Wed 14, 2018 1:13 am 
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Thanks to everyone who replied. I just wanted to say that I have been in this hobby since the late 80s and decided that since I like collecting radios, I needed to learn how to repair them. I started reading books and relying on the occasional call to my uncle who was a fantastic repairman. He was trained by the Army in WWII in electronics and then had his own repair shop. How I wish I could have learned more from him while he was alive. The internet has certainly deepened my understanding, but I always wish I knew more. Chris: Thank you for the explanation I was looking for and the validation about the frustration. I always check every cap for shorts, opens, and correct value even if I don't replace it. Of course I understand that in the radio they are subjected to higher voltages and problems might not show on the cap tester. Greg: Thanks for the link and I did read. Marc: I want to remember what you said about drifting off frequency. My Westinghouse WR8 does that and one day I will dig into it, but it is a bear to work on. Leigh: If it tests bad, I do replace it and would not expect it to go away. I don't replace what appear to be working caps on my radios unless it's one of my "daily drivers". Most of them sit on the shelf for display. I do like all of my radios to work, though. Mark


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 Post subject: Re: weird symptom
PostPosted: Feb Wed 14, 2018 2:33 am 
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MarkinK-zoo wrote:
Leigh: If it tests bad, I do replace it and would not expect it to go away. I don't replace what appear to be working caps on my radios unless it's one of my "daily drivers".
Hi Mark,

There is NO test extant that will tell you what a cap will do next year or next month.

If the set is really a shelf queen, with no possibility of being powered up (power supply disabled), then I see no reason to replace old caps. But if it can be used...

- Leigh

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73 de W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: weird symptom
PostPosted: Feb Wed 14, 2018 6:37 am 
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I can see no value spending parts money on a shelf queen, however I would remove the power cord on them. I have an STC on the bench at the moment, that was cutting in & out, it is going into service. I found a "dry joint" (photo taken) probably it, but I have not as yet powered it. The Wax paper caps in it, I had cause to check, albeit after I had replaces them. The best one at 500V DC was 17Meg and the worst 1Meg.

Whist this ones a commercial job; That sort of leakage can easily cause tubes to run at the wrong operating point and cause overloads: Seven resistors also were failed & replaced. If its not going to be a shelf queen refurbish it. Refurbish does not include wax paper caps being left in situ.

Marc


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 Post subject: Re: weird symptom
PostPosted: Feb Thu 15, 2018 12:02 am 
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Leigh: I have so many radios - several per room. Just can see a reason to use all of them, so they sit, but like them to be in working order because the first thing non-collectors seem to ask is "Does it work?". This always seems so amazing to folks, but not for us who collect and work on them. If I do a repair job for someone else (which is rare) I would replace them all. While we're on this subject, where do people buy their caps? I buy some when the radio meet happens here in Kalamazoo, but that's once a year. Where is the best deal? Mark


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 Post subject: Re: weird symptom
PostPosted: Feb Thu 15, 2018 12:47 am 
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Location: Mountains of Mourne. Ireland.
For Radio capacitors...
Sal's Capacitor Corner and Just Radios, see the ads to the right of this page→

Most of my Electrolytics and other passive components come from Digi-Key in Thief River.
"A delivery charge of $18.00 USD will be billed on all orders of less than $50.00 USD.
Free delivery is offered for all orders of $50.00 USD and greater".

Some people find the parametric search daunting... :shock:

Here is a (parametric search) jump-in page for 50V radial electrolytics.
viewtopic.php?p=2751804#p2751804
also... take a gander at fifties allelectronis.com link.

Greg.

oh... ebay is a real crapshoot for electroltyics. Lol


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 Post subject: Re: weird symptom
PostPosted: Feb Thu 15, 2018 2:08 am 
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Location: North of Mpls, Minnesota
egg wrote:
Most of my Electrolytics and other passive components come from Digi-Key in Thief River.
"A delivery charge of $18.00 USD will be billed on all orders of less than $50.00 USD.
Free delivery is offered for all orders of $50.00 USD and greater".


Where did you find that, most of the small items I buy are shipped first class mail for a couple of bucks. I have never heard of the shipping rates you have described.

Dave


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 Post subject: Re: weird symptom
PostPosted: Feb Thu 15, 2018 2:27 am 
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Ok... It's just for me, 'cause I'm special. Lol.
https://www.digikey.co.uk/en/help/free-shipping

Greg.


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