What is that thump,thump,thump? - diyAudio
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Old 10th June 2007, 07:06 AM   #1
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Default What is that thump,thump,thump?

Hi guys,

I'm working on a vintage Motorola am car radio. The radio powers up but all I get is a thump,thump,thump. Sometimes fast and other times slow. I'm not getting any reception. Any suggestions as to what is causing this?

Thanks for your help,
Steve
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Old 10th June 2007, 07:45 AM   #2
poynton is offline poynton  United Kingdom
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Hi,

It's called "motorboating" for obvious reasons !

Usually caused by dried up capacitors in either the power line decoupling or in the audio output section.

Look for signs of leaking or blown/bulging endcaps.

Replace as required.

Usually, the old Motorolas are very reliable.
Beware of touching the lettering on the tuning scale - it comes off VERY easily.


Andy
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Old 11th June 2007, 09:20 AM   #3
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happen to me and i did the same thing, works prefectly now.
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Old 12th June 2007, 06:57 AM   #4
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I have a cap tester. I'll just go through and check them all. I want it to sound like a row boat again . Are the outputs easy to find for these old radios? I've done a little searching and haven't been able to come up with much.
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Old 12th June 2007, 06:57 AM   #5
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Oh, and thanks for your help Poynton. I appreciate it !
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Old 12th June 2007, 07:51 AM   #6
poynton is offline poynton  United Kingdom
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Quote:
Originally posted by 65blkbkgt
I have a cap tester. I'll just go through and check them all. I want it to sound like a row boat again . Are the outputs easy to find for these old radios? I've done a little searching and haven't been able to come up with much.

Quote:
Originally posted by 65blkbkgt
Oh, and thanks for your help Poynton. I appreciate it !
No Problem !!

The sets are nothing special - just germanium PNP !!! Still available from surplus stores and EBAY.
The resistors and caps can be replaced with modern types.

I used to have over 100 of these from various years - some with tubes
some hybrid. I did the autojumble circuit selling to car enthusiasts.

The data was well published in Television and Radio Servicing Manuals
and may be available from Mauritron (?) in the UK if not in the USA.

Andy
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Old 16th June 2007, 01:24 PM   #7
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Quote:
Originally posted by poynton
Hi,

It's called "motorboating" for obvious reasons !

Usually caused by dried up capacitors in either the power line decoupling or in the audio output section.

Look for signs of leaking or blown/bulging endcaps.

Replace as required.

Usually, the old Motorolas are very reliable.
Beware of touching the lettering on the tuning scale - it comes off VERY easily.


Andy
Hey Andy,

Well, I've decided to go in for my first recap (gulp). This should be an adventure. I already have the replacement caps (minus the PNP) and plan on doing it "one cap at a time" because my short memory span would surely come into play if I removed all the old caps then tried to replace them all. I just looked on Ebay and found a few pnp's which look a lot different than the one on my radio (pictured below). Are these interchangeable with other car radios? The numbers on this are as follows: 2N176 452. Ring any bells?

Wish me luck and I'll let you know how it all turns out. You will find me back here before I'm done. LOL !
Attached Images
File Type: jpg pnp.jpg (99.3 KB, 66 views)
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Old 17th June 2007, 01:35 AM   #8
poynton is offline poynton  United Kingdom
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Hi


http://www.semiconductormuseum.com/P...rola_2N176.htm


An alternative would possibly be OC28 or OC35.
(OC28 is more durable)


Andy
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