Community Sat, 20 Jan 2018 23:01:35 +0000 MYOB en-gb Leroydueck just registered on the site (Leroydueck) profiles Sat, 20 Jan 2018 19:24:26 +0000 Mark created a new forum post in ATA 24 Electrical Power
Lear 60 with no #1 inverter power output.

The inverters are located in the ceiling of the aft bag pit.

For troubleshooting purposes, the #1 (left inverter) is easier to deal with as the 28VDC power input and ground wires are inboard and accessible.

The right side unit's inputs are somewhat tougher to get to.

The first avenue for troubleshooting inverters is "is it getting power"? With the cockpit switch selected on, 28VDC should be present at the selected inverter's main power input lug. This is a large wire, I'm guessing 4 gauge. Power comes through a contactor from the main DC Power Bus.

With this particular problem, power was not preset at the inverter. Starting at the source, there is a 100 amp fuse used to supply power. Visually, it looked burned and warped. A meter lead "carefully" placed through an opening at the top of box showed power at the bottom lug, nothing at the top.

After the fuse was replaced, 28VDC was present at the inverter, but the A/C output was only 25VAC. The inverter's cooling fan was not turning either. Basically, the inverter was failing and the fuse blew in response to the high load.

There are many other areas of failures that can be associated with inverter power. The input and output contactors along with switch controls and any control relays. This particular problem was pretty straight forward as to the failure.

As a side note, I'm not a Lear guy. The batteries "should" be disconnected before EVER messing with the DC supply bus bars. From the access hole where the batteries are located....... getting to the disconnects looked damn near impossible. The left battery could be reached with a guy having a long arm. The right battery..... forget it. I did notice a possible access panel on the right side for accessing the right battery. This is NOT RIGHT. Any time you're working with power, the batteries should be disconnected. How can safe work be done if you can't reach the damn batteries?

The fuse was replaced "hot". A ratchet and socket were used to break the fuse nuts. the rest was done with fingers (and "no" 28VDC will not hurt you). The ratchet was used to tighten the nuts after fuse replacement. Any misplacement of the ratchet causing a power path to ground is going to lead to some "very" interesting sequence of events that could end up killing you or burning up the aircraft. A serious "shame on you Learjet engineers" is fitting for the shitty battery disconnect design.

Lear 60 AMM 24-20-01
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]]> (Mark) kunena Sat, 20 Jan 2018 13:54:40 +0000
Mark created a new forum post in ATA 33 Lights
Right nose taxi light inoperative. Simple enough problem, just power and a ground.

Light removed. Power was verified good on one of the two wires. The ground was intermittent, but moving the leads just outside the bulb housing would give a reading to ground (not a solid ground).

With the suspect area cut out...... no ground at all. What???

Working the wire bundle aft and up from the light assemblies takes you to what appears to be a junction box.

Just a wire guide assembly. At no point was a ground indicated when moving the bundle in this area.

While moving up the bundle into the nose gear well, the meter had to have the ohm's "buzzer" turned on as it was impossible to watch the meter and shake wires at the same time.

At the top of the gear the open was found. I should of guessed as the harness had been previously worked on as evident by electrical tape being wrapped around it.

Upon gutting the harness two wires were found broken. The taxi light ground wire had an environmental splice that had snapped in half (although I was pleased to see someone actually went through the hassle of installing one there). The other wire probably broke when I was opening up the bundle.

A repair was completed on both wires, but I suspect that more will break over time. This area is where the wire bundle moves and bends in response to gear retraction/extension. I'm not sure if any plausible solution is available other than changing placement and slack of the bundle itself. There is a pronounced bend aft of the lower adel clamp.

If wires continue to break in this area, the complete bundle can be replaced as an assembly. A part number is located on the bundle at the gear well wall feed through plug.
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]]> (Mark) kunena Wed, 17 Jan 2018 22:31:22 +0000
swelch just registered on the site (swelch) profiles Tue, 16 Jan 2018 15:35:53 +0000 Mark created a new forum post in ATA 78 Engine Exhaust and Thrust Reverser
Citation X with a continuing problem of the Thrust Reverser "UNLOCK" light illuminated with the T/R stowed.

The system has a control card mounted on the forward wall of the baggage pit. A breakout box used to aid troubleshooting can be installed. The breakout is useful in verifying the proper grounds (supplied via the various switches) in both the stow and deploy positions.

There are 6 possible switches (3 on each side) that can cause this warning. Two unlock switches and one unlatch switch are used on the T/R rails.

The upper and lower unlock switches show hydraulic pressure is present and that the locks are in the deploy position. The unlatch switch located on the back of the rail is activated at the end of T/R deployment. (This is an incorrect statement. The unlatch switch(s) is located between the two unlock switches on the forward side of the rail. The fully deployed switch, shown in the lower picture is used to indicate T/R deployment.)

For a problem as this, one of the four unlock switches would be the most likely culprit. If switch failure has been ruled out, switch rigging should be checked. The outboard set is easily reached..... the inboard set...... are going to take some gutting to access.

Cessna recommended working the throttle laterally to verify if the quadrant switches are not faulted.

As a final recommendation, Cessna stated the hydraulic control valves could be swapped for troubleshooting. (Although, I'd exhaust all other troubleshooting steps before swapping the valves.)

Cessna Model 750 WDM 78-30-01
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]]> (Mark) kunena Tue, 16 Jan 2018 02:33:36 +0000
Rpjmem just registered on the site (Rpjmem) profiles Mon, 08 Jan 2018 14:51:01 +0000