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Brittain B12 accutrack question


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Hello,

i am trying to get my b12 working correctly. Currently the PC system is working as it should. My issue is that the b12 is not tracking to the heading to the DG bug.

After trouble shooting per the manual it seams that the input from the DG is initiating the desired response to the 805 valve when the heading bug is to the right or "+30%", + 5.5 to 6 volts, but when the BG bug is to the left or "-30%" it is not producing the correct negative 5.5 to 6 volts.  Is my issue in the DG or in the Brittain controller?

image.png.f39086b78a776c5136002966846577ec.png

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I installed the B-12 in our C last year.   I'm not an expert, but I did my homework to help advise the A&P on the details of the install.  We got it working with just a little trouble.

I think, and others with more experience might have a better idea, that the DG output is pretty darn reliable.  It receives AC input from the BI-818 DG adapter, and put out AC output back to the BI-818 depending on the degrees of deviation.   The BI-818 takes that AC signal and turns it into +/-10VDC which gets mixed in with the Accuflite signal to drive the BI-805 valve.

Since B-12's are rare as hen's teeth, swapping out the DG to confirm that it isn't the problem is the first best option, I think.

Some folks here on MS have backups of all the Brittain stuff.   Maybe somebody can ship you a spare.   The Edo-Aire 4000-D DG is easy to come by.

Given that the Brittain stuff is entirely Apollo-era discrete electronics, and the document you reference plus schematic, an electronics tech worth their salt should be able to repair the BI-818 DG adapter if there is a problem there.

My problem was- after we installed the B-12, it was reverse sensing.   A left deviation caused a right turn.  This was discovered during ground testing using a standby vacuum pump.   Spoke with a former Brittain employee who suggested swapping the output wire polarity between the B-12 and the B-11 Accuflite.   Problem solved.   I hope you find a solution.   Keep us posted.

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I’ve found errors in the schematics and test set ups. Fred points out an example above. I’ve even had a stray trace in a module.  Was this a working system prior to install?  I’m leaning toward an interconnect problem.

 Which DG do you have and can you provide the interconnect…how you wired it?  I can then compare to what I have in my binder.  It is full of my old mark-ups that don’t mean much at the moment.  Feel free to email flightenhancements@yahoo.com.  

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Thanks for the info 

the DG is connected via a hard wired 5 port female plug. I did try testing for voltage on the plug but did not realize it was A/C, I was looking for D/C.

I will check for A/C power and might jumper out the ports to see if I can get the 818 to send negative DC voltage to the 805.

if that does not work I guess I will remove the 818 controller and try to get it bench tested/repaired.

thanks again for the help!

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36 minutes ago, Rmfriday said:

Thanks for the info 

the DG is connected via a hard wired 5 port female plug. I did try testing for voltage on the plug but did not realize it was A/C, I was looking for D/C.

I will check for A/C power and might jumper out the ports to see if I can get the 818 to send negative DC voltage to the 805.

if that does not work I guess I will remove the 818 controller and try to get it bench tested/repaired.

thanks again for the help!

Check your email.  I just sent some new drawings with my mark-ups.  I don’t think I sent those previously.  Feels like you are close.  My guess is you have one wire swapped…

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If your DG Adapter is like mine, it has test ports for your multimeter on the side.  My DG Adapter was installed up under the left side kick panel near the firewall.  It's mounted in a clip with a thumbscrew.  My Brittain AP stopped tracking the heading bug.  I traced the problem to the DG output not the Brittain components (and had the DG overhauled).  Kevin (former Brittain tech) helped me trace my problem working with me over the phone (he told me to find the DG Adapter and use the test ports).  He also later benched tested my DG adapter just to make sure it was working correctly before reinstallation.  He might be able to still repair one.  I have his number if you need it.  There's both DC and AC flying around that system; you may have to test at the DG Adapter test ports to correctly measure the +/- 5.5 V DC (at +/- 30 deg off the line).  If the DG is unplugged or INOP there will be no output on the DG Adapter test ports.  I believe the 400 hz or 2000 hz (not sure which) is sent to the DG from the DG adapter; then it gets manipulated by the DG synchro and sent back for conversion to DC to drive the Turn Coordinator valve.  You should hear the AC hum if you put your ear to the DG Adapter (whether the DG is hooked up or not).  I have a pin out diagram sketch for the 5 and 7 pin connectors if you need it.  BTW, I believe you should see about 115 ohms between pin A (AC output) and pin E (output common) on the DG; and you should see about 195 ohms between pin D (AC input) and pin B (input common).  If you don't, that could be a quick indicator of a bad DG synchro (mine was bad and open between pins D and B).  I'm not an avionics expert; just a guy with a little experience with this particular problem.  Recommend you don't pull too many things apart until you make sure the DG synchro is working; that's a common easy overhaul.  

DG_ADAPTER.jpeg

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Well I have everything on the bench and did some trouble shooting……

the DG has 112 ohms between A and E, 196 ohms between D and B, the 805 has 99 ohms. Everything seams good on that front but still having issues. With everything hooked up and powered I get full deflection and about 5.8V when the heading bug is 30 degrees to the right, when the bug is 30 to the left I get mixed results, if the 805 valve is not connected I can get the negative 5.8V sometimes, but as soon as I try to hook up the 805 the voltage falls to like a negative .5 volts. 
I don’t think it is the 805 because when I swap the leads it operated to full direction in both directions 

any ideas? 

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1 hour ago, Rmfriday said:

Well I have everything on the bench and did some trouble shooting……

the DG has 112 ohms between A and E, 196 ohms between D and B, the 805 has 99 ohms. Everything seams good on that front but still having issues. With everything hooked up and powered I get full deflection and about 5.8V when the heading bug is 30 degrees to the right, when the bug is 30 to the left I get mixed results, if the 805 valve is not connected I can get the negative 5.8V sometimes, but as soon as I try to hook up the 805 the voltage falls to like a negative .5 volts. 
I don’t think it is the 805 because when I swap the leads it operated to full direction in both directions 

any ideas? 

Mixed results?  I bought several of those five and seven pin connectors thinking I might need to replace them.  I have the specs if you are having connector issues.  

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Have you tried adjusting the gain and centering with the servo control valve connected?  

Check to see how the grounds are set up.  Is the inconsistency related to having the chassis grounded, or not?  Some of this is coming back to me and I seem to recall having a stray trace to chassis ground that would change the results.  

The harness wiring is critical I suggest ringing out the harness and checking interconnections as well.  Can you sketch it out?  I still feel like you might find something there.

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I think on the gyro to B12 we are talking about pins A,E, D, B.  Looking at individual schematics it almost seems like A-A, E-E, D-D, B-B, although this seems too easy. Can you check to see how those pairs are wired?  
 

Also, check combinations of pins to be sure they are not jumpered.  Note that one schematic I sent you  for an S-TEC system shows a pair jumpered.  This doesn’t seem correct now that I look at it, but can’t recall why I kept it.

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I have rang out the harness and it seams to be good? I went from the female port on the blue plug to the sodered connection on the board and have good continuity, I also opened up the “plug” to make sure nothing was shorted out at that connection. 
I have also taken the 818 apart to look for any tracers or shorts or broken connections or burn marks but it looks fine.

I am starting to get in a little over my head, I am okay with electronics but this little box has a lot going on….

maybe if I just put it all back together it will work……

mine last thing, the transformer on the bottom bigger board is definitely energized and I suspect working, the smaller transformer on the top smaller board is not, I need to look into that and see if it marks anything.

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1 hour ago, Rmfriday said:

I have rang out the harness and it seams to be good? I went from the female port on the blue plug to the sodered connection on the board and have good continuity, I also opened up the “plug” to make sure nothing was shorted out at that connection. 
I have also taken the 818 apart to look for any tracers or shorts or broken connections or burn marks but it looks fine.

I am starting to get in a little over my head, I am okay with electronics but this little box has a lot going on….

maybe if I just put it all back together it will work……

mine last thing, the transformer on the bottom bigger board is definitely energized and I suspect working, the smaller transformer on the top smaller board is not, I need to look into that and see if it marks anything.

Call Kevin Westbrook in Tulsa (former Brittain tech).  He's a great guy; spent his life working on these systems; willing to help you over the phone.  5392920474

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Coming to the party late...

Has the AP ever worked?  If so, I'm very skeptical of any harness miswire; bad connection, yes, but not a miswire.  Sounds like you've checked and cleaned all the connections.  From your description (+output, but no -output) I think there is an issue within B-12 output drive.  You ruled out the 805 valve by swapping leads.

Sorry to say, but I think the B-12 needs to be opened up and troubleshot.  Educated guess is the output transistor for the negative drive is bad.

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Thanks everyone for all the help!

I talked to Kevin today and will be shipping him the 818 so he can trouble shoot it.

he seamed confident it can fave fixed.

to answer the question, I have never flown w this AP but was told it was working when removed.

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2 hours ago, Rmfriday said:

Thanks everyone for all the help!

I talked to Kevin today and will be shipping him the 818 so he can trouble shoot it.

he seamed confident it can fave fixed.

to answer the question, I have never flown w this AP but was told it was working when removed.

Please tell Kevin my Britain system is still working great.  Good luck !  

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16 hours ago, Rmfriday said:

Thanks everyone for all the help!

I talked to Kevin today and will be shipping him the 818 so he can trouble shoot it.

he seamed confident it can fave fixed.

to answer the question, I have never flown w this AP but was told it was working when removed.

I sold the entire system to Mr Friday. It was definitely working when it was removed. I was actually reluctant to take it out of the plane since I wasn't sure when I would get the GFC500 installed. Using the switches on the control head was a little weird. I feel like they weren't labeled well, or they didn't make sense to me. The guy I bought the plane from gave me the crash course on using it but in the moment of purchasing it, I was just impressed that the old system worked so well with a new Garmin 650 navigator. Flew it all the way from the south tip of Florida to Kansas City with the autopilot doin it's thing. It wasn't removed until September I think. 

8D4D5D38-A2D9-4289-9487-EF0D5FEFDD6E.jpeg

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I don’t have any doubts it worked when removed, I am also confident that it will work again. I am hoping it is just something stupid from it sitting or from transport or the install.
i have only installed and tried the B-12, I have not tried the B-11, just the heading bug.

I am still happy I was able to come across a entire A/P.

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