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Need Help Diagnosing Electrical Fault?

Piper J3

Well Known Member
I just finishing an uneventful 1.2 hour flight and had a high voltage alarm on the D-180 at 5 miles from final destination. I viewed the EMS screen and saw 14 volts on battery in red arc. I kept manually shutting off the alarm and then landed. All electrical systems were working. High voltage alarm subsided when power was reduced for landing. After landing I reset elevator trim position as I taxied in like normal. Engine shut off was normal followed by the powering down the Master Switch.

I thought the John Deere VR failed now at 245TT. Original Ducati VR failed at 104TT hours but mode of failure then was low voltage and not high voltage.

I have a spare JD VR so I installed by mounting it on the shelf in original location. VR wired correctly and all wiring under cowl looks good.

I turned on the Master Switch and nothing happens. No relay click - nothing.

I detected a strong whiff of electrical smell and quickly disconnected the negative battery terminal. I removed the instrument bay cowling and the smell appears to have emanated from the fuse block/switch cluster. All fuses are good as checked with ohmmeter. I have shined a bright light at the back side of the fuse block and looked down between the circuit boards and don’t see any damaged components. Various capacitors look OK. If I power the D-180 with its backup battery it shows battery voltage at zero with main battery connected. I measure actual battery voltage at 12.9 with a VOM.

I think my next step is to remove the D-180 EFIS and then remove the fuse block/switch cluster for a detailed visual examination. My plane is an early SN so it has the fuse block/switch cluster on the left side.

If anyone has any thoughts I’d appreciate some insight.

Thanks in advance…
 
14 Volts is NOT high voltage. It is normal. If the D-180 alarms at 14 volts, then the alarm set point needs to be raised.
Without the master contactor being energized, the only thing that can emit smoke is the master switch or its wire that connects to firewall D-Sub pin 22.
Or maybe the smoke is coming from the master contactor itself.
Analyze the D-180 datalog to see what the voltage was peaking at. The datalog is csv file that can be opened with MS Excel.
 
After isolating the master relay from power I would check the coil resistance. Battery terminal to front small terminal. I believe it should be about 15 ohms. (guess)
But I suspect it will be ether open or shorted. Bad relay. If it tests bad suspect your master switch may be toasted. (smell) So test the switch contacts for proper operation. P 44 - To ground...open (off)/grounded (on). Check the master relay diode also...


Regards,
 
Diode

A few weeks ago I had some problem when switching on the master switch . One time the switch wire was burning with a lot of smoke, fortunately not flying.
The master relay diode was not working correctly , I replaced it and now all is ok.
I noticed also that I had an overvoltage alarme, reaching 15,8 v , and also a flap runaway alarm. Since I change the diode , no more overvoltage neither flap runaway indication.
Check your diode .
 
In the D-180 electrical system, the small yellow wire that goes to regulator terminal "C" does not have over-current protection. Since the problem occurred after the regulator was replaced, it made me think of that yellow wire. Of course the master contactor would need to be energized before that wire could get into trouble.
 
Joe

Maybe you're on to something. I forgot to mention that when I changed out the VR and still had no voltage through the Master Switch I tapped the Master Relay with handle of screw driver and that is when whiff of electric happened. I forgot sequence of events - kinda like fake news or alternative facts.

I've been studying D-180 electric schematics for master power flow. I just ordered new Master Relay and Diode from Van's. I'm getting ready to head out to the plane now to remove the AV Control Board 12 (Fuse/Switch Circuit Board).

Thanks for your help. Electrical is not my strong suit...
 
About a year ago I did an experiment: shut off the master contactor while keeping the voltage regulator turned on. The charging system kept on working even with the battery disconnected. But the voltage was not stable and varied between 13.25 and 14.7 volts. You can read about the experiment in my matronics post HERE 5th post down. Bottom line is that the charging system is unstable without the battery and the voltage will vary. I suspect this is what happened in Jim's (Piper J3) RV-12. The master contactor opened up for some reason while flying. The charging system kept right on working, although the voltage was unstable, causing the D-180 to give a high voltage alarm. So Jim, there is probably nothing wrong with the voltage regulator that you removed. The problem is the master contactor or its circuit.
 
OK, I just got back from the plane. I removed the AV Control Board 12 and now have it at home for detailed checkout. After studying the electrical schematic I noticed that the original builder of the plane had the Master Relay Diode connected to the battery side instead of the load side of the contactor. I'm thinking perhaps the Master Relay is defective now and may have destroyed itself over time because of improperly wired diode. I have new Master Relay and associated diode on order from Van's. As Joe mentions above, this would explain the over-voltage warning on the D-180 in flight. Thanks Joe...

What I'm still puzzled about is the electrical burning smell when I tapped the Master Relay. Did it back-feed the master switch to ground?

I'll report back on the condition of the AV Control Board 12 when I examine it this afternoon. I will look especially at the master switch and verify that its contacts are "seen" at the pin connector on the backside.
 
The purpose of the diode is to prevent arcing across the contacts of the master switch. The diode should be connected directly across the contactor coil with the banded end connected to the most positive (battery) terminal. The diode has no affect on the life of the contactor. It sounds like the diode was correctly installed. The diode can be tested to make sure that it conducts one direction but not the other.
A burned copper trace on Van's circuit board could account for the smell and non-working contactor. A shorted diode or contactor coil could burn a copper trace.
 
Hi Jim,
If your using the schematic downloaded from Van's...somethings not right.:confused:

See Van's RV-12 D-180 schematic download HERE.

And don't even think about following the VREG circuit...must have run out of orange ink...:rolleyes:

But I think Joe is correct in the diode wiring. To the battery terminal.

Good Reading...on this topic.

Regards,
 
See Van's RV-12 D-180 schematic download HERE.

So, I'm looking at the schematic you reference and it still shows the diode on the load side and not the battery side. The schematic included in Van's digital files also shows diode on load side. My diode is on the battery side. Now I'm confused.

This image per TC's reference...
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21ec77d.png

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My diode installed like like van's instructions...
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25uh5is.png
 
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Update... I have now looked at the AV Control Board 12 and it appears unharmed. From what I can see with bright light and magnifying glasses, no burnt components or foil tracings. Master switch has continuity to pins 21 & 22 on the FW FWD FPCB connector. Master Switch contacts are working.

So, the plan right now is to install new Master Relay from Van's with new diode (proper install still TBD) and then pull fuses and try to power up the Master.
 
Jim, you are correct about Van's schematic showing the diode on the load side. However, the schematic is WRONG. Take a look at plans page 45A-08. It shows the diode on the battery side. Arc suppression diodes are connected across coils. The coil inside of the contactor is connected to the battery side, NOT the load side.
I have faxed a Builder Feedback Form to Van's pointing out this error.
 
Excellent Joe, new diode will be installed on battery side. I hope new Master Relay solves my problem. I'm planning initial power-up so minimum number of items will be connected to the buss. I'd really like to see just the Master Relay energize all by itself and then gradually add loads back on.
 
Another data point

The ES Diode Master is shown on the battery side on the SkyView Schematic.

i-nFXZNnz.png


D-180 guys please ignore the ES-00165 starter relay diode shown in this picture as it exists in the control board on the D-180 panel.
 
Sorry fellas,
I was not trying to create more confusion... Only pointing out that I thought the downloaded version of the wiring diagram was wrong and incomplete. And that Jim would be confused if using it as I was troubleshooting from it. Didn't know the flash version was inaccurate too. Thanks Joe for reporting it. If I run across errors again I know what route to take.

That said the schematics disclaimer instructs as to what information has precedence...

dgfdmMV.jpg


But it would be nice to be all on the same page.


Glad to hear the board is sound.

Regards,
 
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Further update... I tested the Master Relay today and definitely find it broken. I disconnected the load side and then shorted the coil terminal to ground and nothing happens. Coil should have pulled in. So now I wait for Van's delivery of the the new Relay and Diode.

Things starting to make sense.
 
Update 9-20-17.... Today I removed the Master Relay in anticipation that Van's replacement part will be delivered either tomorrow or day after. Not the easiest thing to remove with engine mount and hoses in the way. For those that carry spare fuel pumps, etc. on long journeys you might want to stock this part as well. This is exact replacement PN http://www.ebay.com/itm/COH24115-BX...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

$23.75 incl shipping.
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35n3ez5.png
 
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Additional data point......

For those that carry spare fuel pumps, etc. on long journeys you might want to stock this part as well.

Vans has been selling and using this exact same part for 25+ years.
Based on the information I have, it has had a very low failure rate (I have personally never change one and I work on a lot of different RV's).
 
Thanks for chiming in Scott. Always appreciate your viewpoint and assistance…

Here’s my theory of the failure: I believe the Master Relay opened in flight and voltage regulator then lost its reference voltage. This caused VR to go full output thinking battery voltage was low. Perhaps the Master Relay re-energized when I throttled back for landing (warning stopped when I throttled back). This allowed elevator trim to work in the landing pattern and also allowed trim to be reset as I taxied in. Once I shut off the engine the Master Relay would not pull in again from that point on.
 
The Rotax dynamo will keep on working even if the battery is disconnected. However without the battery, the voltage will not be stable and vary up and down about 3/4 of a volt from its setpoint. That causes the Dynon to give a voltage alarm. The voltage regulator does not think that the voltage is low because it monitors electrical system voltage, not battery voltage. The regulator does not call for full output. The electrical system voltage is still around 14 volts, plus or minus one volt. All electrical loads are still powered by the dynamo like they always are, whether the battery is connected or not. The trim worked because it was powered by the dynamo.
 
Update: I?m still verifying wiring while waiting for the new Master Relay from Van?s. I was convinced that the AV Control Board 12 (fuse/switch assembly) was unharmed even with electrical smell (see post #1). Well I guess it was fake news or alternative facts, because the master switch isn?t working.

I removed the sheet metal protective backing on the circuit board and can now see where the foil tracings have lifted from heat. This is not an easy fix because the tracings are inaccessible as two circuit boards face each other and cannot be separated.

The solution is to replace the entire assembly. I?ve called Van?s and they stock the part but the cost is prohibitive. I?m wondering if someone might have one of these assemblies lying around. Perhaps someone built their own panel or installed a different engine and didn?t use the AV Control Board 12 that was furnished with the kit.

Let me know if you have an AV Control Board 12 and we can work a deal. I?ll also post an ad in the VAF Classified Thread.

Thanks for listening?

Direct email is [email protected]
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2qvv8jr.png
 
I'd tentatively agree with Mike, pending more info about what's actually on those circuit boards. You do need to determine what overloaded that trace.

Does Van supply a *complete* schematic for the a/c, including all the interconnections on that module? If so, it can possibly be repaired. Separating the two boards, & repairing the burned trace, shouldn't be too hard for an electronics tech.

If you have good docs & you want to give repair a shot, send me an email with some more pics. Try to show the burned trace & how the boards are married to each other.

Charlie
[email protected]
(electronics tech in a couple of former lives)
 
I installed the new Master Relay with my new wire that controls it which I soldered to the back of the master switch. Success. Master Relay pulls in and reference voltage shows up at the voltage regulator.

Engine runs and voltage regulator works so main problem is solved. Both ignitions working. Avionics and EFIS are working.

All functions working accept the following:

• Master switch LED indicator does not work
• No LED’s working on any of the panel switches (avionics, landing lights, etc)
• Trim motor not working - fuse OK
• Stall warning not working - fuse OK
• Audible warnings in headset not working

My question - is there something in common for all these items to not have power? Does the master switch also power these items and the fact that it’s own LED doesn’t light mean its not passing power to these other items? When I had power surge from the defective Master Relay could it have damaged the master switch in a way I can’t detect with an ohmmeter? My suspicion is the master switch has an internal fault. I’m also thinking maybe sensitive electronic components got damaged.

Beginning to look like I need to replace the entire Control Board. Anybody have a Control Board left over from maybe a panel upgrade or engine conversion requiring different controls?

Again, any help appreciated…
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jqhsgp.png
 
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Jim, so sorry for your problems. It is beginning to look like the surge cooked several of the more sensitive electronic components, such as the dimmer circuitry, trim servo, audio circuits etc. some of the electronic gurus can weigh in on this, but that's the way it seems to me. Even if you were able to replace/repair individual components, I think tou need to ask yourself if you want to fly behind a module that has been subjected to this kind of abuse.
 
Mike,
Thank you for that excellent schematic!:D

I installed the new Master Relay with my new wire that controls it which I soldered to the back of the master switch.

It may be helpful if you where to draw on the schematic where the trace was burnt, and where you installed the repair wiring.


My question - is there something in common for all these items to not have power?

I would suspect it's not about having power...but having a good ground.


Does the master switch also power these items and the fact that it’s own LED doesn’t light mean its not passing power to these other items?

The master switch itself only supplies power to terminal 1 when ON, which is connected to the voltage regulator C terminal for voltage sensing and the LED anode for operation indication.


When I had power surge from the defective Master Relay could it have damaged the master switch in a way I can’t detect with an ohmmeter?

Possible...but unlikely. You could also try a light probe tester. But remember always isolate the components when troubleshooting. And that this switch internally has 2 different switches, that control 2 different circuits.


My suspicion is the master switch has an internal fault.

It pulls in the master relay, and the regulator is working properly...it's two jobs in life. If the LED is rated at 12 vdc, grounding terminal seven, with switch on should light the light. Verify rating and isolate before trying...

I'm sticking with damaged or missing ground.


I’m also thinking maybe sensitive electronic components got damaged.

Innocent until proven guilty.

Lots of wires and pins here... I would recommend re-seating every connector paying particular attention to P2, a PCB interconnect and double checking grounding wires,pins, and connections.
If needed I would pick out the easiest circuit not working to troubleshoot, and go from there.

Best regards,
 
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