Help! JD 770 Dead!

[Whitey]

OK.......some of you have been following my post in the hydraulics section....well I have completed the JD 7 BH control box repair and have hooked it up today! So I back my 770 in to connect and as I get it close I put the brake on to connect the power beyond hoses to the BH. Now the tractor was at a low idle for I was in a building and when I dissconnected the hoses the tractor labored a little and when I heard that I immediately shut it down. I connected the backhoe hoses to the tractor in preperation to adjust the subframe and when I turned the key........POW! Thats right I heard a pow behind the key switch. No crank no lights dead tractor. I am lost.....I checked the fuses and are OK......I checked the line off the starter to the key switch and have voltage.....I checked the leads out of the key switch and they have voltage. I do not know where to go from here.....someone please help!

 

[DWCox]

I do not know about the 770, but the 790 has a fusible link:

 

[AKfish]

Now the tractor was at a low idle for I was in a building and when I dissconnected the hoses the tractor labored a little and when I heard that I immediately shut it down.

Always turn the tractor OFF before disconnecting the PB circuit. Bad thing for the hydraulic system.. the "open system" pumps are no longer able to circulate hydraulic fluid and will heat up very quickly!

How much voltage to some of the circuits (starter key)? Is your battery still in one piece? The fuseable link should have stopped all voltage readings...

AKfish

 

[Willl]

Ditto what AK said about the PB, that's a big no no.

That "pow" ain't good.

After all your checks you already did, I'd head straight for the pow (ie; your key switch)

 

[Diamondpilot]

My guess is you have blown up your hydraulic pump and it has now locked up the engine. This is a very common mistake many make when not familiar with hydraulic systems. When you disconnected your hoses it left no where for the fluid to go because its a open center system. (A open center system constantly has fluid circulating and when a action is called for like to lift the FEL it diverts the fluid to that component while normally if nothing is being used the pump is simply circulating the fluid through the system and back to the reservoir tank.) In a split second you fried the pump. This is going to be expensive. Probably a new pump and replace the fried electrical components. The last pump I replace for a friend just due to age was nearly $800. The pop you heard was a electrical component blowing when you tried to start a stuck engine. The engine is stuck due to the locked up pump.

Chris

 

[the bear]

had this happen to a neighbour and he busted the crank shaft at the pump end hope not though just something else to consider

 

[Whitey]

OK I am curious...........some of you say I have fried my pump......not good....so if that is the case why do I not have lights? For those of you that say I fried the switch......I have voltage out when the switch is operating. I thought about this as I went to church this morning and could it be that I had a very low idle with increased load on the tractor by the BH......and when I turned the switch I blew a safety???? The fused link checked out OK....the tech manual said to jump the starter......but I am not wise to that idea yet. If the pump was burned up then how come when I turn the key on I cannot get lights.

 

[Diamondpilot]

I think what happened is you blew the pump and then you blew the electrical components when you went to start it, too much load on the electrical system. You will always have voltage to the starter as long as hooked to the battery and its making a good ground connection. If you have voltage coming from the key switch to the starter then maybe I am wrong about the electrical components. I still think you engine is sized up due to the dead headed pump. It is not going to crank with that situation. As for the lights not working that is a mystery? I still think you are missing something electrical. Check the input side of the fuse box and the output side of each fuse to see if you have power.

Chris

 

[irwin]

First take a breath.. okay? how did you test for voltage from the switch to the starter? that would mean the trigger wire has power, it shouldn't til you try and start the engine.

Do not use the starter to crank engine yet, turn it over with a wrench/socket at the crank if possible, if not find another way to manually turn it over. Let us know what happens.

I had a battery blow up by over loading it and it made a loud pop...

 

[Whitey]

I wish I had read Irwin's post first......ohhh well......the tech manual said to jump the starter. So I did. At first it clicked real loud......and the engine moved at each time I touched the hot lead. Sparks also. The third time I did it I had lights. Everything seemed fine. But when I went to crank the engine ........nothing. So I jumped it again and the thing went flat again.....no lights......no nothing. Back to square one again. i8 did put mytester from the hot side of the starter to the selenoid and it showed voltage......or should I say a ground at the selenoid.