GPS light illuminate on recall (737-800)

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GPS light illuminate on recall (737-800)

Postby novansky » 21 Dec 2017, 08:49

Good day all boeing lovers,

Now I'm facing a problem "GPS light illuminate on recall (737-800)". Herewith I share the resume of t/s:

Ref FIM 34-58 task 802:
*Bite MMR#1,found No Red Lt Ill. LRU OK.

*Bite MMR#2,found No Red Lt Ill.LRU OK.

*IRS Mode Selector Unit check found no Fault Code Appear.

*MCDU check and compare output data from GPS#1 and GPS#2 found DATA Same/No Different.

*check for Clock#1 n Clock#2 found No Abnormalities.

*Cross Change IRS Mode Selec Unit with other A/C problem still exist, part back to ori

*Try to replaced MMR 1, problem still exist, part back to ori

*Try to replaced MMR 2, problem still exist, part back to ori

*Try to replaced IRS MCU with PN 69-37399-13, problem still exist, part back to ori

*Inspect Both GPS Antenna connector no found Corrosion/Water trap.

Can you help me to solve this problem? I count on you...
novansky
 
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Re: GPS light illuminate on recall (737-800)

Postby maro12 » 21 Dec 2017, 21:12

Good Day Novansky,

Have You done any wiring checks?

As per SSM 34-58-11, GPS fault logic, after recall GPS light will illuminate if: (GPS 1 LABEL 273 BITS 26-28 SET OR NO UPDATE FOR 6 SEC) OR (GPS 2 LABEL 273 BITS 26-28 SET OR NO UPDATE FOR 6 SEC).

I do not remember what info is carried on Label 273 from top of my head, but I suspect it is "GPS Fault" status sent by MMR. You checked both systems and they both look working fine, so maybe one of the databus connections to IRS MASTER CAUTION UNIT is faulty? (Which would meet condition "no update for 6 sec"). As the same databus gives input to FMC, and You wrote that all FMC info from GPS looks OK, I would inspect carefully IRS MASTER CAUTION UNIT connectors D2271 and D2269 and do con checks (i/r + o/r) of the databuses MMR1->IRS MCU and MMR2->IRS MCU.

Let us know the progress on T/S and any findings.

Thank You.

Best Regards,
Maro12
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Re: GPS light illuminate on recall (737-800)

Postby novansky » 22 Dec 2017, 09:04

Dear Maro12,

My team was performed wiring chk "only" between IRS MCU to ground. Not the db conn MMR->IRS MCU.
But the problem a little bit strange, when the IRS MCU Electrical Connector cleaned up the GPS light on recall solved. But, a few times (I don't know exactly the precise time) the problem show up again.

And when my team try to do system test of GPS, ref AMM 34-58-00/501 it not go as well as the AMM.
When both of the MMR's circuit breaker open, the GPS light not illuminate anymore (after approximately 10s).

Thanks for the suggestion to wiring chk the connection between MMR->IRS MCU, I'll forwarded to my team ASAP.

Warm regards,
Novansky.
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Re: GPS light illuminate on recall (737-800)

Postby maro12 » 22 Dec 2017, 10:39

Hello Novansky,

You also can use Arinc429 databus reader to check status of Label 273 bits 26-28 from MMR1 and MMR2 and check databus activity on IRS MCU connectors. This would show You wchich MMR or MMR databus gives the trouble.

Best Regards,
Maro12
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Re: GPS light illuminate on recall (737-800)

Postby novansky » 22 Dec 2017, 11:20

Hi Maro12,

Can you tell me the specific name of A429 databus reader?

Your info might help us so much.

Regards,
Novansky
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Re: GPS light illuminate on recall (737-800)

Postby maro12 » 22 Dec 2017, 17:19

Hi Novansky,

There are many Arinc429 Databus readers available, from siple ones to more advanced where You also can simulate (transmit) labels.

An example of the task where Boeing ask You to use 429 reader and gives You example Part Numbers is altimetry test of ADMs: please see AMM TASK 34-11-00-780-802 Altimetry System Test Para C. Tools/Equipment for details.

In the links below also some exmples:

http://www.avionteq.com/document/Avionica-RSU-Manual.pdf

http://aeroexpress.com/wp-content/uploads/2014/10/Bus-Master-UsersManual-9_13_05-Rev-A3.pdf

In Your case from info You provided, both GPS systems give position, clocks get the input, FMS gets the input, I would look for some poor connection in wiring, bad crimping, bad contact etc.

With A429 reader You will be able to check if any of MMR actually gives set Label 273 bits to Fault, or if there is an input to MCU at all.

Good Luck, let us know findings.

Best Regards,
Maro12
Last edited by maro12 on 22 Dec 2017, 21:11, edited 1 time in total.
maro12
 
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Re: GPS light illuminate on recall (737-800)

Postby maro12 » 22 Dec 2017, 21:07

Sorry, I just noticed in first link I sent is description of Avionica RSU 1 and only FDR application. This is quite powerful tool, I used actually RSU 2 for FDR data live read, data extract, Arinc 429 Tx/Rx, You can use it for EFB download etc. capabilities depend on applications (Software) You purchase.

Here how it looks on supplier page:

http://avionicainc.com/products-3-4-2-2/#top

Anyway, I guess for Your problem You do not need such powerful tool.

Best Regards,
Maro12
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Re: GPS light illuminate on recall (737-800)

Postby novansky » 23 Dec 2017, 02:54

Dear Maro12,

Noted FYI and maybe we will do wiring check as ur suggestion or will check M469 Annunciator and Dimming Module on P6 its related to master caution unit refer to SSM.

So, any other suggestion in case of our problem? Coz u said it don't need such a powerful tool.

Regards,
Novansky.
novansky
 
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Re: GPS light illuminate on recall (737-800)

Postby maro12 » 23 Dec 2017, 09:01

Good Day Novansky,

Use multimeter, non specific.

Best Regards,
Maro12
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Re: GPS light illuminate on recall (737-800)

Postby novansky » 23 Dec 2017, 09:56

Hello maro12

Noted FYI and thank you, will be shared to my team on duty tonight.

Regards,
Novansky.
novansky
 
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Re: GPS light illuminate on recall (737-800)

Postby novansky » 24 Dec 2017, 01:03

Dear maro12

After inspect GPS antenna #2 found coaxial cable connector (TNC right angle type) broken at K-Grip sleeve missing 3 grips of 6 total. Is it possible to be the root cause?

Regards,
Novansky.
novansky
 
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Re: GPS light illuminate on recall (737-800)

Postby maro12 » 25 Dec 2017, 19:00

Dear Novansky,

From information You provided:

When both of the MMR's circuit breaker open, the GPS light not illuminate anymore (after approximately 10s).


-You are writing "anymore", why? Did it work before?

a)If Yes, do the annunciator lights test and check if lamps are ok,

b)If lamps are ok and GPS light does not come on when You open both MMRs CBs, the problem is somewhere at the indication side of the circuit.

Lets review the facts: With both MMR CB pulled, both databuses coming to IRS MCU are not active, FAIL and FAIL condition is met and GPS light should come on after 6-10s.

I would concentrate on indication part of the system, from IRS MCU to begin.

Also from information You provided, I am assuming GPS systems are working fine, but to double check there are few more ways to confirm it, as example:

-FMC SENSOR DATA and/or FMC SENSOR STATUS (depends on a/c config) show GPS(MMR) status, see below video regarding this check:

https://www.youtube.com/watch?v=X14FnZYMZtU&index=46&list=PLSlru5PbHgUH8AMT4PB48nlHXHqNME7TC

You said that GPS position shows, BITE on MMRs is ok, therefore, as antenna circuit is tested during BITE, I would exclude this from possible causes (of course I do not know all details and I might be wrong).

Also, You mentioned before:

when the IRS MCU Electrical Connector cleaned up the GPS light on recall solved


I really would not expect the cause was in "dirty connector", not in this location. I would look really closely there, inspect all area really in detail, pushback pins, broken connections, loose contacts etc. You mentioned You replaced IRS MCU, what was the system behaviour with new IRS MCU?

Pay attention to details when troubleshooting.

Good Luck.

Best Regards,
Maro12
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Re: GPS light illuminate on recall (737-800)

Postby novansky » 26 Dec 2017, 06:15

Dear maro12,

Last night, my team has replaced the gps coax ant #2 d/t sign of damage and it solved until now on transit.

We always monitor if the problem comes on again.

Regards,
Novansky.
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