[GMAs]

First off Bob.. you need to check your schematic again... as the starters and all the rest of the ships power goes thru the master contactor... yep it does... the starters don't get their power by a different means... they get it from the master and then send it to the starter contactors... if you want to try something take the masters switch and turn it off... and see if you can still start the engines... smile... now the only thing that still is connected when the master is off... is the clock... no more ... no less...

ON TO ERNIES PROBLEM…..

Ok Ernie... you gave them all the symptoms... for a heavy electrical load... but, no circuit breakers popped out... that means that its a inductive load...

First order is to get the service manual out and turn to the page in the back which shows the schematic of the wiring... (we make the mechanics do this too...but, I usually make them sit at the table and go through all the possibilities and then make a list of the symptoms and items that may cause it...) from that we can get a good picture in our mind of what the system is doing.. from the way it should to the way it isn't...

[here lets take a example... if the gear pump was shorted what would the symptoms be... Ok we put on one side of the page pump shorted... and on the other we put all the possibilities of how it would effect the system... high current, lights dim, no sound, etc.. etc.. see it is logical stuff that can help find the problem]....

SQUAT SWITCH…..

So... the squat switch is one area to start with...lets put a safety jack under the nose jack point and leave the gear on the ground… turn the master on ,gear pump ckt breaker in..., and put the gear handle in the up position… the gear doors should open and then stop.. and the pump make a groaning sound… turn off the master… or you can leave the handle in the down position.. and with the master off.. hand pump down the gear doors… and stop… and then visually inspect all the wires and the oleo strut for full compression of the squat switch as you lift the nose off the ground with the jack… on the jack point… and the strut extends the switch should be in full contact… BE VERY CAREFUL ABOUT THE MASTER SWITCH AND THE GEAR MOTOR CKT BREAKER... WHICH SHOULD BE SAFETIED..(PULLED AS PER THE SAFETY WARING) AS WE DON'T WANT TO GET INTO THE GEAR COMING UP OR THE DOORS CLOSING WHEN WE ARE IN THE NOSE GEAR WELL AREA... The pump and master should be off for this test…. With the gear up handle in position…. If in fact that squat switch was not functioning... either by the fact that the wires at the knuckles or bend points are open.. then you would have had the pump motor for the gear running under load.. the gear doors would have opened up... which you didn't say they did... The lights won't change until something moves….

THE TEST POINTS… for the squat switch is located on the pilots side up in the forward area of the nose gear well… it has a little rubber boot over the terminals… here is where you want to attach your volt ohm meter… after you remove one of the wires going to the squat switch…so as to isolate it from the rest of the circuit. Test and then replace being careful not to over torque the nuts on the terminal strip… you want it tight though and make sure to replace the boot over the studs when you are done… so it doesn't interfere with the wheel or other parts…


... however, I don't think this is your problem

CONTACTORS….

what we want to do here is go across the devices'... and check for voltage... with the system master switch on… you should not get more than 1 volt.. if you do.. check it out further... and replace the item. first from the battery... touch the test lead to the stud of the battery positive side.. then to the cable attachment point on the master contactor... then across the master then to the pump contactor...yep it has one inside on top of the wheel well... then to the pump... going across these items will tell you if you have a problem inside it... now if you have a current meter...clamp.. you might want to put that on and see what the current draw of the motor is...

…. However, I don't think this is your problem either… but, a look see first thing… as from here things get expensive….

GEAR PUMP…..

Next you didn't say the pump was running... you said it was quiet... I mean you should have heard it come up on line and start to load up.. but, wait we have one other clue...

The under voltage light was coming on... when you put the gear handle in the up position... which indicates that the alternators were putting out before and now they are not able to meet the demand... so something is pulling the buss power down.. and if it gets so far down... your not going to be able to make the ckt breakers go pop... because they are not handling enough voltage/current... besides if it still is within the limits of the breaker.. it will not open up...

So lets take a look a the main item the pump... yep.. the pump motor has brushes in it too... and if they get too worn.. guess what they do... high resistance short ……ahhhh...


As skyking says.. the solenoid's are the next item that I look at... but, we can check all of these things real quickly by hand pumping with the master on.. from inside the plane... if the gear doors open on the cycle... and the gear gives resistance to the pump after they are open... good... now in the up position with the plane jacked up all the way around... you should be able open the doors and start to move the gear…by handpump.. again the ckt bkr for the pump motor should be pulled for this test… listen for the selos to click.. and then feel them if they get warm... your working... if they haven't been cleaned... which is more a gear down problem... you need to do that too... while your in their... (every 2 years routine maintenance at annual time)


But,.... from what you said so far.. I would think the pump motor is bad... not a cheep item either.. but, you don't have to get the whole power pack... the pump motor will unbolt right out of the plane... by its self... we had one before that had a bad segment in the motor.. and it just wouldn't keep running... and you don't want to let it recover and then think things are ok.. they are not.. and you need to find the problem and have the bad part replace... G.M> GMAs