SOS Vibrator Troubleshooting

[bob865]

Hey Guys,

I've finally narrowed down my starting problems thanks to the help of mooneyspace to a problem with my shower of sparks system.  I thought at first it was just a bad SOS vibrator box since I didn't hear it when I turned the key past both.  However while she was in for annual my mechanic was testing and found that it is working.  It just didn't activate until the key was pushed and you can't hear over the starter.  With that said, my mechanic was saying when he tested per Don Maxwell's article he doesn't get a spark.  He said he does hear a change in the sound when the cylinder reaches near TDC where it should be firing.  I also asked if he had any power out at the output of the vibrator when it was vibrating and he said no.

I say all of this to ask, is there a simple way to test the SOS box?  I've been searching and the only testing I've seen on here is the Don Maxwell article.  What I'm thinking I should be able to do is:

1.   read 12V-ish at the output of the vibrator when it's running (depending on frequency and update rate of meter etc).
   1. This will tell me the vibrator works
2. read 12V-ish at both the P lead and retard contact at the magneto
   1. This will tell me the switch is functioning.  If it's missing at either contact or if ground is present this tells me the switch is faulty
3. If 1 and 2 read correct, the the magneto has to be faulty

Does this sound correct or am I reading the schematics all wrong?

[carusoam]

See if you can find @Urs_Wildermuth recent experience with his SOS...

Urs put together some nice writing on the subject...

There is a copy of the SOS manual around here somewhere as well.  Probably in the downloads section?

Another MSer wrote about his experience with the ignition switch at the same time... it had a broken connection that failed to deploy the SOS or the timing change for the starting magneto...

Apparently, the SOS does wear out, but takes about 50 years or so to do it...

PP ideas off the top of my head...

Best regards,

-a-

[bob865]

I've read his whole thread.  Actually chimed in and asked some questions to help my own troubleshooting along which got me to this point.  I know the issue is in the SOS, but what is missing in all of the threads I've read is how to verify the SOS box works or doesn't.  I don't have a scope, but I'm thinking I should be able to connect my regular meter it should read somewhere below 12V but above 0V telling me I am getting power out.  If the power makes it all the way to the mags then I know the switch is ok too.  From there I would suspect the cap inside the SOS box so that it isn't providing enough power to the mag to generate the spark or causing the frequency to be too high to generate a usable spark.

[MIm20c]

I don’t think the SOS output is a simple 12v output. I think it is a high frequency burst of energy that would be hard to measure with a voltmeter. I would ohms out the wire lead you are referring to to make sure you have good connections. Make sure all the connections are tight on the back of your starter switch. 

[carusoam]

Is there a resource for OH of an SOS box?

I read the SOS maintenance/owners manual a long time ago... I don’t recall enough detail... it’s posted around here somewhere if you need it...

Best regards,

-a-

[Guest]

9 hours ago, bob865 said:

I've read his whole thread.  Actually chimed in and asked some questions to help my own troubleshooting along which got me to this point.  I know the issue is in the SOS, but what is missing in all of the threads I've read is how to verify the SOS box works or doesn't.  I don't have a scope, but I'm thinking I should be able to connect my regular meter it should read somewhere below 12V but above 0V telling me I am getting power out.  If the power makes it all the way to the mags then I know the switch is ok too.  From there I would suspect the cap inside the SOS box so that it isn't providing enough power to the mag to generate the spark or causing the frequency to be too high to generate a usable spark.

Search for manual X43003-2 it covers the SOS system.  If you can’t find it email me and I will send it to you.

Clarence

[Urs_Wildermuth]

On 20.3.2018 at 2:20 AM, bob865 said:

  It just didn't activate until the key was pushed and you can't hear over the starter.  With that said, my mechanic was saying when he tested per Don Maxwell's article he doesn't get a spark. 

Well, this very much looks like the box is broken. We replaced ours (despite the fact that it sounded and it actually emitted some sparks) and all trouble are gone.

Someone mentioned that you can change the condensator inside the box too. I plan to send my old one to Don or anyone else who knows how to REALLY test them and can possibly repair it and then keep it as a spare. But the $600 spent on the new box were well spent money and should have been spent 3 months and x... money earlier. Lesson learnt.

[bob865]

Thanks @Urs_Wildermuth I think that's the point I'm at now.  I sent a few e-mails around to shops that look like they may overhaul this.  She is in annual immediately after having a G5 installed so she has been a major money pit this month.  Hoping I can save a few on overhaul vs. buying new.  I went through and verified all wiring an everything works.  Turns out we even have a spark at the plug at the advance point.  My mechanic mistakenly pulled the wrong spark plug originally when checking for spark.  But it sure looks weak to me.  The sparks in the starter vibrator are way brighter than those at the spark plug.

[mike_elliott]

On 3/19/2018 at 9:28 PM, carusoam said:

There is a copy of the SOS manual around here somewhere as well.  Probably in the downloads section?

Yep, I just put the 2 Shower of sparks manuals there.

[Urs_Wildermuth]

45 minutes ago, bob865 said:

Hoping I can save a few on overhaul vs. buying new.  I went through and verified all wiring an everything works. 

That was my thinking at it was dead wrong in retrospect. We were literally taking everything else apart back and forth and still ended up getting a new box. So to "save" a new 600$ box I ended up spending 10 fold that money. Bet your whatsit, that lesson WAS learnt and it was very expensive too.

As I said, someone told me that the boxes can be repaired and all they mostly need is a new condensator. So I would suggest take it to someone who KNOWS them or fedex it to someone who does and let him assess the box. Field testing does not do anything in the end unless you know exactly what to look for. If you want to fly reasonably fast again, order a new one and THEN get the old one overhauled as a spare. That is what I now will be doing with mine.

Best information you can get right now is WHO actually knows these things to the point of repairing them or making the call whether it's repairable or not.

[TWinter]

It was easier to just replace it. My old one is in my hanger in the box of junk pile. It served it purpose, but 40 yrs is 40 yrs. We've all spent $500-600 on things for our birds that are far less important and more consumable..ie plugs, oil change or a full tanks of fuel. If it starts, helps hot starts and is consistent in starting it might be the best money spent in a while.

 

-Tom 

[bob865]

Well after a few phone calls this morning, saving money by doing an overhaul on it doesn't look like an option.  Looks like I'm going to be ordering me a new one.  However one guys mentioned that Slick (since I have slick mags installed on my plane) has an option called SlickStart that replaces the old Bendix boxes. It's a capacitive discharge solid state (no points) version that is supposed to provide even higher starting energy to the plugs.  Has anyone used it or have any info on it?

 

 

[yvesg]

On ‎2018‎/‎03‎/‎22 at 5:16 PM, Urs_Wildermuth said:

Well, this very much looks like the box is broken. We replaced ours (despite the fact that it sounded and it actually emitted some sparks) and all trouble are gone.

Someone mentioned that you can change the condensator inside the box too. I plan to send my old one to Don or anyone else who knows how to REALLY test them and can possibly repair it and then keep it as a spare. But the $600 spent on the new box were well spent money and should have been spent 3 months and x... money earlier. Lesson learnt.

Urs, I am an electronic technologist and if you want to send me the box, I will fix it and build something (and/or create a procedure) to facilitate the testing of the box. I will send you a private message.

Yves

[Andy95W]

2 hours ago, bob865 said:

Well after a few phone calls this morning, saving money by doing an overhaul on it doesn't look like an option.  Looks like I'm going to be ordering me a new one.  However one guys mentioned that Slick (since I have slick mags installed on my plane) has an option called SlickStart that replaces the old Bendix boxes. It's a capacitive discharge solid state (no points) version that is supposed to provide even higher starting energy to the plugs.  Has anyone used it or have any info on it?

 

I put one on my first M20C.  It was better than the SoS.

For a fuel injected airplane that was having start issues and the SoS box was starting to die, I would definitely get the Slick Start.

For my current M20C, I'll buy the $25 worth of parts and repair the SoS box.

[TheTurtle]

On 3/27/2018 at 9:38 AM, Andy95W said:

For my current M20C, I'll buy the $25 worth of parts and repair the SoS box.

do you have a parts list?

[Guest]

9 hours ago, TheTurtle said:

do you have a parts list?

Does this help?

[TheFlyingScott]

I just installed a SlickStart in my M20C and it made all the difference in the world! Instead of cranking hoping the engine catches before the battery runs down, she starts in two blades every time ! No muss, no fuss, just Bam and away you go