Radio Preppers

General Category => Technical Corner => Topic started by: gil on March 28, 2014, 02:09:51 AM

Title: MTR Scare!
Post by: gil on March 28, 2014, 02:09:51 AM
I just about croaked tonight... Well, not literally, when my beloved Weber MTR puffed out a cloud of foul smelling smoke! There was a popping noise as well. I unplugged it and opened the case, expecting a big mess in there, given the amount of smoke that came out. Nothing! No burnt traces or components, no visible damage. I checked everyting, power plug, etc. The smoke seemed to come from the front, between the PCB and the top of the case. Finding nothing, I plugged it back in, it works! Proceeded to call a station in Morocco, who answered my first call! There were many other stations trying.. WTH?

I've never experienced anything like that. I'm not complaining mind you, I would have been very upset if my MTR had died, more upset than if my KX3 blew up.. :-\  (I'd be pretty upset too..). I wasn't even touching the darn thing, just had my earphones on.. Voltage was 11.4V, so no trouble there. It's a mystery! It still smells aweful...

Well, time to go to bed. I'll try the MTR again tomorrow. I want to take it with me camping this week-end...

Gil.
Title: Re: MTR Scare!
Post by: cockpitbob on March 28, 2014, 07:53:44 AM
Get a magnifying glass and look carefully at the big capacitors.  Something in the radio went short then cooked itself into an open circuit.  It's not guaranteed to stay open though.

Good luck with it!
Title: Re: MTR Scare!
Post by: KK0G on March 28, 2014, 08:29:30 AM
I agree with Bob, something definitely cooked in there and my guess is a capacitor. Time to get out your magnifying glass and check it all over very closely, fortunately you don't have much to check with such a small PCB.
Title: Re: MTR Scare!
Post by: gil on March 28, 2014, 08:56:16 AM
Hello, I agree on a capacitor.. Not much else that could do that out of those tiny surface-mount components. They all look spotless though.. The front I think is the only side with electrolytic capacitors, three maybe.. I could change them all I guess.. I posted on the AT-Sprint Yahoo group and asked for advise..

Gil.


Sent from my iPhone using Tapatalk
Title: Re: MTR Scare!
Post by: KK0G on March 28, 2014, 10:50:33 AM
The best diagnostic tool I've used to locate burnt components is my nose, probably a little more difficult tool to use in your situation though with such a small board. Might help to verify though once you remove the suspect(s) from the board.
Title: Re: MTR Scare!
Post by: gil on March 28, 2014, 10:53:16 AM
QuoteThe best diagnostic tool I've used to locate burnt components is my nose, probably a little more difficult tool to use in your situation though with such a small board.

Yep, tried that, too small... One guy on the AT-Sprint group says it wouldn't be a capacitor but likely a final transistor. I doubt that since the smoke was coming from the other side and I wasn't transmitting. And of course since I have 20 spare transistors, it won't be that. However I have no spare capacitors, so it's most likely  ::)

Gil.
Title: Re: MTR Scare!
Post by: KK0G on March 28, 2014, 11:20:10 AM
If it does end up being a capacitor you don't have, let me know. I have a decent stock of them and would be happy to drop one in the mail.
Title: Re: MTR Scare!
Post by: gil on March 28, 2014, 11:34:34 AM
Thanks Chris. Those are tiny elctrolytic capacitors, the size of a pea.. I'm sure Mouser has them for peanuts.. The MTR works just fine though, but I feel a bit weird about leaving it like that after that incident..

Gil.
Title: Re: MTR Scare!
Post by: cockpitbob on May 29, 2014, 09:28:13 PM
So Gil, what ever happened with your smoking MTR???
Title: Re: MTR Scare!
Post by: gil on May 29, 2014, 09:49:30 PM
Well, nothing! All functions work properly and I have the same power output. As if it never happened :o So I am leaving it at that..

Gil.
Title: Re: MTR Scare!
Post by: cockpitbob on May 29, 2014, 10:55:08 PM
Most engineers just throw "plenty" of capacitors into their designs.  Only if it's going to fly into space or have millions made will an engineer take the time to determine how much power supply bypass capacitance is really needed.  My only concern is that something that smoked and blew open circuit could some day decide to go short circuit.  But that probably would have happened by now.  I'm glad this didn't happen to me.  It would drive me nucking futz not knowing what let its smoke out.
Title: Re: MTR Scare!
Post by: KK0G on May 29, 2014, 11:54:42 PM
Quote from: cockpitbob on May 29, 2014, 10:55:08 PM
Most engineers just throw "plenty" of capacitors into their designs.  Only if it's going to fly into space or have millions made will an engineer take the time to determine how much power supply bypass capacitance is really needed.  My only concern is that something that smoked and blew open circuit could some day decide to go short circuit.  But that probably would have happened by now.  I'm glad this didn't happen to me.  It would drive me nucking futz not knowing what let its smoke out.
When I first started to learn electronics (and believe me I still have a LOT to learn) I could never figure out what all the .01 capacitors in a schematic did - here's one, there's another one, and yet another, hey what's this one over here? I couldn't really see what they were for because from my meager electronics knowledge it sure looked like the circuit would work just fine without them. Sometimes the author of an article would even suggest adding more bypass capacitors that weren't shown on the schematic. Maybe some of these guys were heavily invested in capacitor factories? ;D
Title: Re: MTR Scare!
Post by: mdmc on June 07, 2014, 01:17:02 AM
It sounds silly, but you can use a drinking straw to sniff through and isolate the area somewhat. You can cover the nose end with a piece of pantyhose material or something similar to protect yourself.
Title: Re: MTR Scare!
Post by: gil on June 07, 2014, 01:25:25 AM
Yep thanks, tried that.. Nothing found.. It's been a while now, and the MTR works flawlessly, so I'm not going to bother..  ::)

Gil.
Title: Re: MTR Scare!
Post by: cockpitbob on June 07, 2014, 09:57:29 AM
Old electrical engineers remember Mad Man Muntz.  An off-beat entrepenure.  One thing he did was make TVs cheaper than anyone else.  They wouldn't work out in the country with weak signals, but most people live in the cities where the signals are strong.  His method of reducing cost was simply to remove a part and see if the design still worked.  If not, he'd put it back and try another.  A method dubbed "Muntzing" (http://en.wikipedia.org/wiki/Muntzing) the design.  Your MTR Muntzed itself.   8)
Title: Re: MTR Scare!
Post by: KK0G on June 07, 2014, 10:47:38 AM
Quote from: mdmc on June 07, 2014, 01:17:02 AM
It sounds silly, but you can use a drinking straw to sniff through and isolate the area somewhat. You can cover the nose end with a piece of pantyhose material or something similar to protect yourself.

Quote from: gil on June 07, 2014, 01:25:25 AM
Yep thanks, tried that.. Nothing found.. It's been a while now, and the MTR works flawlessly, so I'm not going to bother..  ::)

Gil.

I just had a vision of Gil with pantyhose on his head and a straw sticking out from his nose........... not pretty ;D
Title: Re: MTR Scare!
Post by: gil on June 07, 2014, 11:15:38 AM
Gee.. I don't party that hard  :o

Gil.
Title: Re: MTR Scare!
Post by: mdmc on June 08, 2014, 09:55:22 PM
I found the answer! Ghosts in the Machine!
(http://digitalculture-ed.net/arthurh/files/2009/09/Ghost-in-the-machine1.jpg)
Title: Re: MTR Scare!
Post by: Quietguy on June 08, 2014, 10:59:45 PM
Wow, that looks just like RadioRay after a night on the town before he settled down.

Wally
Title: Re: MTR Scare!
Post by: RadioRay on June 19, 2014, 02:07:26 PM
Yeah - I was a LOT skinnier back then!


>Ray
Title: Re: MTR Scare!
Post by: gil on June 19, 2014, 10:34:45 PM
QuoteYour MTR Muntzed itself.

It sure did  :o I had a contact with Morocco soon thereafter, so performance did not suffer.. Must have been an "extra" component...

Gil.