P-Lead 30K ohm resistor location?

[Bud_Keil]

I am diagnosing a problem with my left mag RPM on my D10 EMS equipped 0-360 engine with Slick mags. I am not original builder. During a mag check, the left mag reads 0. It used to fluctuate wildly initially but now reads 0 so I am assuming a broken wire or a bad 30Kohm resistor. My question is, where should the resistors be located?

The Rev A installation instructions (Revised 10/18/2005 and when the airplane was built) shows the 30K ohm resistors between the P-leads and the D10 pins 32 & 33 (no ignition switch in the illustration on page 13 of 45). The Rev I instructions (dated Aug 2010) show the 30K ohm resistors from the ignition switch to the pins 32 & 33 (page 3-4) with the P-leads going directly to the ignition switch. My ign switch only has a single wire for each P-Lead which leads me to believe that the resistors are in the wiring leading directly to the mags. Additionally, each of my mags two (2) wires on the P-Lead terminal with one of the wires on each matching the color per the D10 schematic.

Assuming I find the culprit, is there any benefit to locating the 30Kohm resistors IAW the latest schematic location (between the Ign switch and the D10 unit?

 

[GKC Aviation]

I normally put them at the key switch, leaving the P-Leads intact.

 

[Akash]

I am using 150 kohm resistor .and slick magneto.but problem is that RPM fluctuation. Every time RPM problem some time RPM over shoot.and some time when throttle is on idle RPM ,RPM goes to Zero.I change the every thing but problem is same
.please help me

 

[preid]

Akash- At what RPM does the fluctuation occur?
Is it a IO540? Rotax, etc? each engine requires more or less resistance. (an IO540 needs the 150K, smaller engines something smaller)
RPM at Idle tells me you have too much resistance, but than at higher RPM you shouldnt be seeing any fluctuations?

 

[preid]

Bud;
On my setup the resistor sits at the MAG switch (or keyswitch for others) the way its setup is the 32/33 wires are soldered to L/R plead wire with the resistor in between, than the plead ground is connected to the ground side of my switch. So in summary the resistor is soldered to my switch along with the 32/33 wires and plead sits on the other side of resistor to Left mag (in your case)

When you are at "both" does the RPM seem normal? what happens when you switch to Left- to the EGTs? are they the same? climbing? decreasing? how does that compare to the Right side with the EGTs (including RPM in this case), does RPM go down?

 

[Bud_Keil]

Bud;
On my setup the resistor sits at the MAG switch (or keyswitch for others) the way its setup is the 32/33 wires are soldered to L/R plead wire with the resistor in between, than the plead ground is connected to the ground side of my switch. So in summary the resistor is soldered to my switch along with the 32/33 wires and plead sits on the other side of resistor to Left mag (in your case)

When you are at "both" does the RPM seem normal? what happens when you switch to Left- to the EGTs? are they the same? climbing? decreasing? how does that compare to the Right side with the EGTs (including RPM in this case), does RPM go down?

In the 'both' position, the rpm seems normal as does the right mag. Only the left mag drops to 0. I haven't paid attention to the EGT's but there is a normal rpm drop when switching to a single mag. I'll try to evaluate the EGTs on my next flight.

 

[Akash]

Akash- At what RPM does the fluctuation occur?
Is it a IO540? Rotax, etc? each engine requires more or less resistance. (an IO540 needs the 150K, smaller engines something smaller)
RPM at Idle tells me you have too much resistance, but than at higher RPM you shouldnt be seeing any fluctuations?

Yes it is lo 540.when throttle is an 1200 RPM .RPM goes to zero for one second .I don't off any mag switch.but after one second RPM goes to again 1200RPM.this problem is only for warm up.but when oil temperature goes to green limit.this problem automatically solve

 

[Akash]

And when I put throttle to 27 RPM.only for 2 to 3 second RPM goes to 3300 RPM.I know this is indication problem .but do every thing but problem is same

 

[preid]

Akash
have you checked left side and right side only? Does it do it for both or only one of those two?

Replace the 150k resistor, or check that it’s not loose. You’re using the correct resistor size.

 

[preid]

In the 'both' position, the rpm seems normal as does the right mag. Only the left mag drops to 0. I haven't paid attention to the EGT's but there is a normal rpm drop when switching to a single mag. I'll try to evaluate the EGTs on my next flight.

so If there is a normal drop on the left, yes, confirm the egt on left, should go up, than down again on “both”. If that works replace the resistor on left. I’ve replaced a few throughout the years.
let us know how it works out

 

[jakej]

Akash - a picture of the wiring/resistor location may also be helpful here.

 

[Bud_Keil]

Found the problem. The pin 32 wire coming from the D10 EMS unit had a butt splice attaching the 30K ohm resistor lead. The other end of the resistor had the ring terminal crimped to it that lead to the P lead on the left mag. There was apparent arcing (black residue) between the resistor lead and the ring terminal. Also, the resistor lead was loose inside the crimp. I won't get a chance to go flying for a few days but I will check the EGTs during mag check and confirm the results. If I continue to have problems, I will terminate the 32 wire at the ignition switch and place the 30K ohm resistor in that line, away from the hostile engine environment.

 

[Bud_Keil]

Well, I thought I found the problem. Just got back in the air after a condition inspection. I performed a mag check during flight and the left mag still shows 0 rpm. The EGTs do increase on a single mag, then quickly return to normal when on both.
I reused the original 30K ohm resistor after I measured and verified the value. Guess I’ll have to buy some resistors and wire it near the ignition switch after all. I plan on doing both 32/33 wires in the off chance that the wires are swapped at the D connector and the right mag lead was the problem all along. Stay tuned.

 

[Raymo]

The resistor should be between the EMS and switch P-Lead wire, not switch and mag. When you ground the mag, it is no longer sending RPM information (not firing). Also be sure the switch wiring goes to the correct mag.

 

[Bud_Keil]

Solved my problem. Removing both 30K ohm resistors located on the mags (schematic circa 2006) and installing new ones between the ignition switch and the D10 EMS unit (latest schematic) solved the issue.

 

[DBRV10]

Your problem was the resistors/crimps and not the location. I prefer the old method of the resistor at the mag. That way the wire running up into the EMS (long antennae) is less likely to spread noise into other things behind your panel. Having the mag switch run is enough noise generator (should be screened).

That being said if the resistor is at the end of the screened run and then into the harness it should be OK, but either way works.