WDM-T/S

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1 week 3 days ago - 1 week 3 days ago #1604 by dynamics
WDM-T/S was created by dynamics
Regarding two files I have just emailed, would you mind showing on the diagram how the voltmeter and resistor should be connected in series in connection with highlighted text of trouble shooting?should I start the engine in order to apply charge pressure on the pressure switch during trouble shooting?
Last edit: 1 week 3 days ago by dynamics.

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1 week 3 days ago #1605 by Mark
Replied by Mark on topic WDM-T/S
I never got any Emails.

If we're still talking about the CSD oil pressure switch, then no resistor is needed. You're looking for a intermittent ground on the signal wire from the switch to the light in the cockpit. Everything is checked in reference to ground (meaning one meter lead is connected to frame or some verified grounded piece of metal).

We're talking "one" wire here. The signal wire..... it's touching or close to touching some piece of metal that  provides a ground path.

As stated before, you use a megger to find these problems. You disconnect the pressure switch and either hook up at it or the other end of the wire (at the overhead panel). Connect the other megger lead to aircraft ground. Try 250 volts, 500 volts, or higher. You want to see the meter indicate damn near infinity. If it is half scale (10Meg - I'm just throwing that out), you've got high resistance to ground on that wire. "That" is what is causing the light to flicker.

Start disconnecting intermediate plugs to isolate it. Start shaking wire bundles while someone is looking at megger. If it jumps (up or down) that's the problem area. Open up the bundle. Start physically looking at the wire length.

Check the plug pins at the CSD.

That wire "is" your problem. Find out where it's shorted!!!!

As to your other question about running the engine to make the switch????? Just jumper the plug to simulate that..... but that "will" put a ground on the suspect wire. You don't want or need to do that.

There is a piece of test equipment called a TDR. If you're shorted, it''ll tell you the distance from where you're hooked into the wire.

Almost all warning lights Boeing, Douglas, Airbus, Gulfsteam.... have power on one end of the bulb filament at all times. It is the provided ground on the other side of the filament that turns it on. You are picking up a ground on the signal wire going to the CSD.
 
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1 week 2 days ago - 1 week 2 days ago #1606 by dynamics
Replied by dynamics on topic WDM-T/S
I have just sent the files again
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Last edit: 1 week 2 days ago by dynamics.

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1 week 2 days ago #1607 by Mark
Replied by Mark on topic WDM-T/S
I've never heard of the resistor method. Exactly how is to be accomplished (safely) with the engine running?

Just by the fact that the CSD oil pressure light goes out (on the overhead) when the engine is started should prove the switch is operational.

Please..... check out the wiring as described above and on previous post.
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