i was thinking about this after i made my last post and the control handle did come to mind, i know they had issues with these at one time but since then i believe they did re-vamp the handle to a new style so i doubt that is it.

As for the tech you know that is an independent? unless he had worked for yale in the past i doubt he has the software to interface with the control system on this truck.

According to the manual i have on this unit it has a curtis control system , a 1310 master control unit and 2 1243 motor control units and possibly an optional 1254 pump controller. The premium trucks had this pump controller and generally came equipt with a premium display. Since your display doesn't seem to have any special display properties i'm suspecting it is just contactor hydraulics? The way to distinguish this easily is when you activate the hydraulic function the motor just goes wide open to a preset speed, no scr variation, its either on or off and you hear a contactor engage when you move the handle. That is something no effecting the truck so we won't get into that.

When you have the top panel off i'm sure you noticed 2 motor controllers and the master controller in there, make sure these connectors are clean as well. And also there should be one or 2 contactors for 'traction or line' and if it has contactor hydraulics there would be one for that. Check these contact tips and make sure they are not carboned up or burnt/pitted out. The 'line' contactor if carboned up can cause alot of undue issues due to bad connection from carbon or burnt tips.
These controllers also have an LED light on them, when they are in normal run mode the light will be a steady blink , on... off...on...off, but if there are any issues with the system they will blink a code much like a car or forklift does that has a MIL light, it should flash the code in sequence in digits, like if it had a code 43 it would flash 4 times, then pause for a second and then flash 3 times. It will repeat this code as long as the fault is present.

Now as far as the drive system, like i said, there are a couple ways you can get into that, 1- through the dash display which is rather cumbersome and not my first choice. 2nd - the laptop which would be my first choice and thirdly - curtis makes a handset which can plug directly into the controllers. I have used both the laptop software and the handset and now i believe what you probably need to do is go into the main controller and reset the settings of the truck back to default. There is a setting in there that is probably out of range and causing the truck to not run properly. Since you are not getting any errors on the display this is my only thoughts on why it keeps kicking out.
Not long ago i had a yale order picker doing almost the exact same thing, but it was throwing errors and someone had gone in and made adjustments and inadvertantly changed a setting they shouldn't have causing the system to have a conflict causing the truck to quit running and it was intermittant just like you are experiencing.
If you can get ahold of either of these devices we may be able to get some things straightened out without much more undue pain and suffering (so to speak) ;o)
Curtis makes 2 ways to gain access to thier motor controllers directly...

1 - the 1313 handheld programmer (last time i checked these run around $600 and they come with different access levels, you want one with at least a service or dealer programmer level, the user access level will not gain you access to the menu systems you would need to make all the necessary changes you might need)

2 - 1314 PC Programming Station (not sure of the pricing on this but i suspect it would be around the same price. ( it comes with the same access levels so you still would need a high level access not a user access level.

If you want to learn more about these go to curtisinstruments.com and look in the products page.

Of course you still would need the service manual to make sure you get the controllers set the way Yale designed them to run with this truck to insure correct operation.

Usually when i would have these kind of issues with these units after eliminating the battery and/or connection issues i would always go into the controllers and make sure all the settings were correct and see if anyone had been in there futting around with the settings trying to make it run faster or something like that. In most cases i always found someone had and i would have to reset the system back to default settings. Once i did this the unit generally came back to life the way it should.

oh its a 1995 just so you know

i dont see anything that resembles display faults ,just hours and state of charge in bars.nothing thats shows any kind of numbers at all. as for my experience i m a starter and alternator guy 36 years now, i ve got 3 tow motors 2 propane,and this one electric ( need for it size) i know only real basic on this machine ( not much) i purchased form a customer who does lift trucks had the bug when he had it but cant seem to locate the problem at all. like your honesty to LOL, i ll check to see if he had the ability to hook up a laptop to it,hes an independent so im not sure. it was kinda strage when i just unplugged the circuit board ,turned switch on and off the worked fine for a while now ,no go. buy i may go out in a day or two and work aok. i will locate a service manual asap, i do have a part manual i did locate. i m going to keep packing away. i also did do a direct power relay to activate forward and reverse,worked fine. i do have no doubt the potempiometor in handle is fine and connections i went over pretty well. i just wonder if circut board may be the culprit

stman,
ok so there is not a premium display on this truck judging from your answers, just a bdi / hourmeter (standard curtis 840 display)

still this standard display should show battery charge, hours and also will display faults when they occur

The ESC/FA communicates with both premium and standard displays and shows faults when they occur.
So once again i ask, when this problem occurs do any codes display on the display? When you are ON the truck trying to drive it. If yes tell me what numbers you see pop up.
If nothing comes up on the display then you can also go into the control system using the multifunction handle and see what error codes are in the history. You can also clear any history and make any adjustments to the system you need.
The only thing to doing this is you NEED TO BE EXPERIENCED working within this control menu. DEFINITELY NOT for the novice, and you WILL NEED the service manual.
As far as knowing Yale trucks? I worked for them for almost 18yrs... i think i know their trucks fairly well ;o)

My question to you is are you a forklift tech? or just an end user with some mechanical experience trying to 'do it yourself' ????
If the latter then you have a long road ahead of you to learn this machine. Go to your Yale dealer and buy a service manual.
If you need a quicker fix then call them out to fix it, they can hook up to the controller and see what is actually going on with a laptop.

I'm not saying this to be rude or short with you, it is just on this truck the control systems are advanced enough that even a seasoned tech can have trouble getting to the bottom of a problem, in the training modules we take they are classified as advanced so training is more involved than normal. And being an intermittent failure this makes it even more difficult to pinpoint the problem.

Good luck

i look after some. have yet to experiance your problem on my trucks. but i have on other brands/models which is why i made that suggestion.

only display is the battery charge thats it,no codes no lights,nuttin.guess i m looking for someone that knows yale esc0030/0040 really well

i dont suppose it shows any errors on display when this occurs?

other than checking the grounding on the machine no, my first electric lift do its slow going. i just comes and goes.best luck i had was plugging and unplugging circuit board, and now that doesnt do.i honestly feel its a small problem,just cant locate. everything work fine too,just forward and reverse

have you checked for shorts to frame?