Help Please with computer on link belt 3400 Q

[sawdustmaker]

I bought a 3400 q a few months ago that had been sitting for several years. it was parked because the stick was badly broken and supposedly no other issues. The computer was replaced not long before when someone used a welder to jump start it, killing the computer. Now i can get no response out of the computer. its getting power at the 24v supply and from the key switch but nothing out except for two ~5v signals i haven't traced on the schematic.
I can give the monitor 10v and it will come to life but the computer still is not functioning. the lights in the computer do come on then but still no control of the throttle or any of the hydraulic solenoids. Its possible the computer has crapped out

I wish i had a way to test the computer. Nothing in the service manual looks like any help besides the schematic. has anyone messed with these enough to point me in the right direction?

 

[sawdustmaker]

I really don't want to spend $4000 on a computer if there's something else that could be wrong.

 

[sawdustmaker]

All the powers and all the grounds seem to be right except there is no 10v supply going to the monitor.

 

[John C.]

As I recall the Q series wasn't a lot different than the C2 series. There was little if any diagnostics and you just had to bite the bullet sometimes to find out if the unit was good or bad. A call to the nearest franchised dealer might be in order and could save you a small bucket of money just for a phone call.

 

[sawdustmaker]

Im not sure what you mean sir. Can they test it?
I havent called to price the "controller" but the PO told me he paid $4000 for the one thats in it now. ....i mean on my bench now.

I took the case off the computer and the transistor that controls the "2 stage travel" is burnt to a crisp. I really dont think one burnt up transistor is the cause of my worries. I think im going to take it to the local circut baord place on monday and let them look it over.

 

[wilko]

When the computer on my Kenworth went out, the local shop sent it somewhere to be remanned. You might ask ask the local diesel shop if they have a place to send it.

 

[bvfdfire]

hopefully your electronics guy can fix your controller, if not, it appears that a khr1794 controller is the replacement controller for your link belt. it seems also to be pretty common across the various sumitomo variances and sizes even.

 

[sawdustmaker]

My local circuit board place was no help so I went to link belt dealer and priced the controller. They want $4600 for it but they were nice enough to give me a part number. I put KHJ1785 in Google and for $650 one showed up at my door. I plugged up last night and it acts no different. I'm totally stumped. I have spent hours studying the schematic and checking wires with a test light trying to find any other possible issue with no luck.
The throttle motor cycles when the key is turned on so I believe the motor driver is functioning. What else can I do?

 

[CatToy]

Do you have the service manual? My LB 330LX manual had troubleshooting guides in the electrical section. For me they Kind of helped narrow down where the fault is at. I has a problem where one of the wire loop connections had been sitting in oil for several weeks and gave a fault that would not let the unit start.

 

[laycobeau]

Email me a copy of the schematic and maybe I can point you in the right direction.
beau.bowlan@lei-corp.com or call 866 529 8365 mon to fri 8:00am to 5:00pm cst

 

[sawdustmaker]

Email me a copy of the schematic and maybe I can point you in the right direction.
beau.bowlan@lei-corp.com or call 866 529 8365 mon to fri 8:00am to 5:00pm cst

Email Sent.

Thank you

 

[sawdustmaker]

Do you have the service manual? My LB 330LX manual had troubleshooting guides in the electrical section. For me they Kind of helped narrow down where the fault is at. I has a problem where one of the wire loop connections had been sitting in oil for several weeks and gave a fault that would not let the unit start.

Will look through them more carefully. I have before and it pointed to "replace controller" I may have missed something in there.

 

[sawdustmaker]

I should have noted I have no prior experience reading schematics.

 

[mikebramel]

If the two speed output was burnt did you disconnect that from the circuit when you hooked up the new one?

 

[sawdustmaker]

I have made some progress but not found a solution yet.
There is no power coming from the "Bypass relay" in the right hand switch panel. I put power to it and the computer woke up but just beeps and flashes. I cant get it to tell me what the fault is in English, and i cant read Japanese. I tried to do the initial reset described in the book but it wouldnt let me with the fault. Does anyone know what letter is for link belt machines? My manual is for JCBs and it says, after selecting 220 for the model, to select E for JCB

 

[laycobeau]

Is wire # 310 hot (+24v) and does the diagnosis reset switch do anything?

 

[sawdustmaker]

I apologize for the tardy response but i have been out of town working.

Yes #310 has power. But the reset button does nothing.
#312 has no power. By backfeeding power to 311/312 i was able to get everything to work except the "bypass" throttle control. So i deduce that the bypass relay is to blame.

My throttle motor was also bad (the bolt that hits the limit switches broke off) but for the most part i think everything is working now.

Many thanks to Laycobeau for pointing me in the right direction!