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 Post subject: FM Not Working. Tubes?
PostPosted: Nov Fri 18, 2022 11:28 pm 
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Joined: Sep Sun 04, 2022 4:38 pm
Posts: 18
Location: Minneapolis, Minnesota
Hi All. New to restoration but I did just complete my first recapping of all paper caps on my Motorola Model: 13KT15CW Chassis: Ch= HS-677. That went really well thanks to the help I got on this forum! Now I have a radio question.

Both AM and FM worked fairly well prior to and after recapping. Now however, the FM has stopped working. The only thing I can think that may have triggered this was that I removed the tubes (to clean them) and after replacing them is when the FM stopped working,

Although I realize it could be any number of things, I've read in some posts that one cause could be tube-related. I don't have access to a tube tester but I thought I'd throw it out here to check on which tube might be the most likely suspect. If there are any obvious choices, I would probably pick up a new one and try that.

Can anyone identify some basic troubleshooting for this? Thanks!
Attachment:
Motorola Schematic 1.JPG
Motorola Schematic 1.JPG [ 772.9 KiB | Viewed 356 times ]

Attachment:
Motorola Cabinet Tube Diagram.JPG
Motorola Cabinet Tube Diagram.JPG [ 2.11 MiB | Viewed 358 times ]


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 Post subject: Re: FM Not Working. Tubes?
PostPosted: Nov Sat 19, 2022 12:41 am 
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Joined: Nov Sun 04, 2007 5:01 am
Posts: 4156
Location: Redding, CA
Location: Redding, CA
It is likely that one or more tube pins are not making good contact with the sockets. Are all filaments lighting up?

Norman

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 Post subject: Re: FM Not Working. Tubes?
PostPosted: Nov Sat 19, 2022 2:31 am 
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Location: Tucson, Arizona U.S.A.
Location: Tucson, Arizona U.S.A.
Did you get the tubes back in the right sockets?

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Who's that swimming in the punch bowl?
It's Walter Wart, the freaky frog!


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 Post subject: Re: FM Not Working. Tubes?
PostPosted: Nov Sun 20, 2022 1:59 am 
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Joined: Sep Sun 04, 2022 4:38 pm
Posts: 18
Location: Minneapolis, Minnesota
Braithwaite wrote:
It is likely that one or more tube pins are not making good contact with the sockets. Are all filaments lighting up?

Norman

Thanks! Planning to check that out and clean the contacts. Several of the FM tubes have strong filament glow but there are a couple that although there is glow, you can barely see it.


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 Post subject: Re: FM Not Working. Tubes?
PostPosted: Nov Sun 20, 2022 2:02 am 
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Joined: Sep Sun 04, 2022 4:38 pm
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Location: Minneapolis, Minnesota
Jim Mueller wrote:
Did you get the tubes back in the right sockets?

I did double check and yes they're in the right place. Funny, I hit up a local experienced repair guy today and that was the first thing he said too. That's part of this hobby I enjoy the most - troubleshooting to find out the fix is the simplest thing you missed!


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 Post subject: Re: FM Not Working. Tubes?
PostPosted: Nov Wed 23, 2022 6:13 pm 
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Joined: Sep Sun 04, 2022 4:38 pm
Posts: 18
Location: Minneapolis, Minnesota
Braithwaite wrote:
It is likely that one or more tube pins are not making good contact with the sockets. Are all filaments lighting up?

Norman


Update:Thanks Norman. I cleaned the leads and hit them with CRC QD. The FM is back and for the most part sounds pretty good. Thanks for the tip!

Regarding filaments, yes they all showed some light - more on some than others. It begs the question, in considering the health of a tube, how bright should the filaments be?


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 Post subject: Re: FM Not Working. Tubes?
PostPosted: Nov Thu 24, 2022 2:52 am 
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Location: Tucson, Arizona U.S.A.
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Quote:
how bright should the filaments be?
[/quote]
As bright as it should be for that type tube of that age. It varies considerably..

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Jim Mueller

Who's that swimming in the punch bowl?
It's Walter Wart, the freaky frog!


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 Post subject: Re: FM Not Working. Tubes?
PostPosted: Nov Thu 24, 2022 6:51 pm 
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Joined: Jan Thu 01, 1970 12:00 am
Posts: 5020
Location: Boston, MA
Heaters either work or they don't. Some are bright yellow, some dull red, and in tubes for battery radios the filaments are not visible at all.

-David


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 Post subject: Re: FM Not Working. Tubes?
PostPosted: Nov Thu 24, 2022 8:56 pm 
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Location: Qualicum Beach, Canada
You removed and cleaned the tubes but did something else as well? Bent a couple of leads together, bumped the bandswitch? Is your FM antenna connected as before? Any exposed coils that might have got disturbed?

Not discounting a tube issue, but usually if the tube worked before it doesn't just drop out, unless it was actually dropped. :x

Also go over your previous work, solder connections, inspect them with a strong light and magnifier. Reheat any that haven't flowed onto the metal.

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