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S-Tec 30 GPSS internal fuse

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recapen(at)earthlink.net
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Posted: Thu Mar 25, 2010 5:55 am Post subject: S-Tec 30 GPSS internal fuse

Anyone else out there with S-Tec 30 and GPSS?



Any of you having issues with the internal fuse in the GPSS module?  



Mine blew once during construction and was a real pain to ship back and have S-Tec (whatever their name is now) solder in a new one.  I attributed that to using a power supply (even with a battery) to run my panel during build testing.  It has since blown again and I am trying to figure out a way to not have to go through this PITA another time.



More importantly, what is causing this little critter to pop in the first place?  



The rest of the panel works fine with no other avionics issues.  I have gone back to my engine monitor to look for any recorded voltage spikes....the highest I have is 14.0 which should be within the normal operating range of the system (?).  I have spike catching diodes on my relays and have a process for powering up and powering down stuff like this to prevent it from happening for other reasons.



Your thoughts please,

Ralph Capen

RV6A N822AR (at) N06 55hrs

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nuckolls.bob(at)aeroelect
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Posted: Thu Mar 25, 2010 6:19 am Post subject: S-Tec 30 GPSS internal fuse

At 08:33 AM 3/25/2010, you wrote:


<recapen(at)earthlink.net>



Anyone else out there with S-Tec 30 and GPSS?



Any of you having issues with the internal fuse in the GPSS module?



Mine blew once during construction and was a real pain to ship back 

and have S-Tec (whatever their name is now) solder in a new one.  I 

attributed that to using a power supply (even with a battery) to run 

my panel during build testing.  It has since blown again and I am 

trying to figure out a way to not have to go through this PITA another time.



More importantly, what is causing this little critter to pop in the 

first place?



The rest of the panel works fine with no other avionics issues.  I 

have gone back to my engine monitor to look for any recorded voltage 

spikes....the highest I have is 14.0 which should be within the 

normal operating range of the system (?).  I have spike catching 

diodes on my relays and have a process for powering up and powering 

down stuff like this to prevent it from happening for other reasons.



     It's likely that the problem has nothing

     to do with anything you are doing . . . or

     not doing. The fact that some electro-whizzy

     for airplanes includes and internal fuse is

     itself reason to query the skills/design

     goals of the manufacturer. I have on occasion

     included fusible link type performance inside

     a product . . . designed to prevent burning traces

     on an ECB should some downstream failure put a

     trace at risk. But real fuses (read fast acting

     and not particularly robust) does give pause to

     wonder why it's in there.



     If indeed the fuse is nuisance tripping because

     of a REAL transient event on your system, then

     I'm wondering if the electronics downstream of

     that fuse were tailored to live with transient

     events known to exist on the system (I.e. DO-160

     style qualification).



     How much current does this electro-whizzy draw

     in normal operations? Do you know what size the

     fuse is?



     Bob . . .

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recapen(at)earthlink.net
Guest

Posted: Thu Mar 25, 2010 11:06 am Post subject: S-Tec 30 GPSS internal fuse

Good points Bob,



This is a TSO'd device - part of an autopilot whose wiring is protected by a 5 amp fuse.  I'll be taking a magnifying glass out to look at the markings on the unit to determine its ratings.  I agree with your questioning of the potential lack of DO160 compliance from a common sense perspective.



My initial research in to these types of fuses show that there are holders that could be installed to make the fuse ultimately field-serviceable...albeit painfully field serviceable.  This would allow the retention of the fuse the manufacturer deemed required for whatever their reasons.



I'll post the info on the ratings that I discover.



Ralph

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recapen(at)earthlink.net
Guest

Posted: Fri Mar 26, 2010 9:50 am Post subject: S-Tec 30 GPSS internal fuse

I called their tech support...their guy told me it is a 1/2A Slo-Blo surface mount fuse.



We then talked about what could cause this thing to go.....which led to my education on how these units interact with each other.



The 10VDC that this fuse protects is used to excite the heading system - in my case a Century NSD 1000 HSI.



Back to checking my wiring for shorts...didn't find any last time - but I'll still check...55hrs without a blip.



It is listed as DO 178b though.......



Any more thoughts?



Thanks!

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bgray(at)glasair.org
Guest

Posted: Fri Mar 26, 2010 10:02 am Post subject: S-Tec 30 GPSS internal fuse

I seem to recall that DO-178 covers software only.



DO-160 handles the electro-wizzies.



I could be wrong though.



Bruce

www.Glasair.org 



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recapen(at)earthlink.net
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Posted: Fri Mar 26, 2010 10:21 am Post subject: S-Tec 30 GPSS internal fuse

Would explain according to Bob the existence of the fuse......

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nuckolls.bob(at)aeroelect
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Posted: Sat Mar 27, 2010 2:48 pm Post subject: S-Tec 30 GPSS internal fuse

At 01:01 PM 3/26/2010, you wrote:

 	  Quote: 	
		  



I seem to recall that DO-178 covers software only.



DO-160 handles the electro-wizzies.



I could be wrong though.


	


  You are correct.



  Bob . . .

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nuckolls.bob(at)aeroelect
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Posted: Sat Mar 27, 2010 2:50 pm Post subject: S-Tec 30 GPSS internal fuse

At 12:48 PM 3/26/2010, you wrote:

 	  Quote: 	
		  

<recapen(at)earthlink.net>



I called their tech support...their guy told me it is a 1/2A Slo-Blo 

surface mount fuse.



We then talked about what could cause this thing to go.....which led 

to my education on how these units interact with each other.



The 10VDC that this fuse protects is used to excite the heading 

system - in my case a Century NSD 1000 HSI.



Back to checking my wiring for shorts...didn't find any last time - 

but I'll still check...55hrs without a blip.


	




   Aha! It did not occur to me that the fuse could be

   protecting the GPSS innards as a power source

   as opposed to a load.



   It makes sense that if you burden the internal

   power supply with both internal and external

   duties, it might be well to protect that output.



   What you might consider is a temporary 10vdc power

   supply with an LED indicator that annunciates

   an overload. This could be wired around the GPSS.



   You could do this with "jelly bean" parts.



   Bob . . .

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