Friday, August 5, 2016

Thomas NBO

Today's job was a Thomas Nut Bank Out cart.  Intermittently it would stop moving and sometimes would go again after cycling the key off then back on.
This machine is hydrostatic drive with electronic control. It has two joysticks for transmission control. One is for transmission ranges, and one for forward, neutral and reverse. The forward and reverse is the one giving us fits today.
I called the manufacturer for a schematic or manual to get some direction but was told that it wasn't happening because it is a 2008 machine and they had not written any.
It took me a while to find out how the system worked because of the lack of any books or diagrams but it is not that complicated. It can be traced out by hand from connector to connector. The fact that it would work for a long time and then just stop also added to the time it took to figure out the cause.
The expert on the system was available by phone but the machine was located in a really bad service area so I had to keep leaving the machine to call him. He was quite convinced that one of the six micro-switches in the joysticks were malfunctioning. I wish he would have been right it would have saved me a lot of time and frustration.
What I found was that the back up alarm was spliced into the harness between the joystick and the controller. The wire that supplied the current to the controller to tell it to shift to reverse also turned on the back up alarm. Once I got the machine to act up, I captured this wave form at the hydrostat controller on the pump unit.
This capture is with the machine shifted to reverse and the throttle pedal depressed (the throttle must be depressed to turn off the anti-coast valves.  That is not relevant to this problem.) Forward is the yellow trace and green is the reverse trace. As you can see both forward and reverse are getting powered. This causes the transmission control to just say forget it, I'm not doin' nothin' until you make up your mind. Even when shifted back to neutral the pattern continued. I had to find what was feeding the transmission control with this bad signal. It was a pulsing signal about one second long and 3/4 second off. My first thought was turn signals but they checked out as normal.
I had the machine shifted to forward and the foot pedal depressed with the key on and engine off when I walked around to the back of the machine and heard the faint buzz coming from the back up alarm. BINGO! I had found it!  The back up alarm had a ground stud with a metal tab connected to it and a mounting screw to ground it to the frame. The nut was loose causing a less than perfect ground. I tightened the nut and recorded the following captures.



Shifting from reverse to forward.
This was a tough one mostly because of the lack of service information but also the environment. It is much harder to find these bugs when it is 105 degrees outside and there are harvesting machines buzzing around you with the dust that goes along with them. I'm glad it is finally fixed!

Friday, May 27, 2016


I have heard a ton of people say Keep It Simple Stupid!  That is very good advice that is so often not followed. 

Complex machines with multiple sensors and controllers can overwhelm. I worked on a chipper recently that kept shutting down the feed rollers because of a drum speed warning. 

A sensor monitors drum speed so that if the machine bogs down the feed disengages. The mechanic working on it went straight to the sensor and had no way to actually monitor the sensor output. He got bogged down in the complexity of the system and worked on it all day. 

Turns out the sensor was doing its job and warning that the drum speed was too slow because the belt was slipping. After tightening the belt to specification the machine worked normally. 

Mechanics have it harder today than ever before. We have to find out if there is a problem or if the monitoring system just thinks there is a problem. 

Computers can often detect subtle incosistentcies before any noticeable symptoms appear. A code will often appear for an engine misfire long before you can hear the miss. If you start looking at the crank sensor assuming that it is giving you erroneous information you can derail your diagnosis. A compression test might seem to be a pain but until low compression is ruled out it could be th cause of the error. 

We have all done it. Just add my reminder to all the other people that have told us to KEEP IT SIMPLE STUPID!

Friday, May 20, 2016

Make a wrench

What do you do when you are out in the field and you need a tool that you do not have?  Today I found myself in that situation. I had strainer inside a hydraulic tank that I couldn't get loose. I didn't have the right size wrench to take it off. A pipe wrench wouldn't fit. So I found a piece of scrap iron and cut out of 55 mm wrench.  It only took a few minutes to make. I could've fought with that strainer half a day without the correct tool.

I will save this wrench for future use but I will probably clean up some of the rough edges before I throw it in my toolbox. It wouldn't work if it was a high torque application, but I didn't need a lot of force I just needed more reach.

I have a lot of tools in my toolbox that I have made over the years. I can imagine that someday my son will inherit my toolbox and wonder what the heck I was doing. That's much the same way as I look at my grandfather's toolbox now.

Wednesday, May 18, 2016

Don't get sucked into loser jobs!

Do you ever find yourself working on something that you just hate to work on and you know you're not going to make any money from it?  That is where I found myself today. 

It was an older machine that someone else started working on and could not finish.  I usually have a rule about these kinds of jobs but it is a good customer and he played the "I really need some help here!" card on me.  He told me that the fan came off and hit the radiator.  That is not too hard to fix normally, so I told him I would do it.  When I went to his shop and saw the machine I knew I was in trouble. 

The part of the story that he left out was that it was on the road when the fan came off and they towed it without disengaging the wheel hubs.  This is a hydrostatic transmission and it blew the seals out of a wheel motor.  As if this was not bad enough the wheel motor was worn out and there were no parts to repair it.  A new wheel motor was very expensive and would take several weeks to get.

Now the machine is torn down in the middle of the shop for what seemed like forever!  Fast forward to today.  The parts are here and I have to put it all back together.  The new motor doesn't fit because the flange is machined wrong.  The good news is that the machinist says he can fix it....for a price.

The fan pulley doesn't line up either.  The engine was a fresh rebuild and the water pump shaft is not long enough for this application.  Now we know why the pulley came off in the first place.  The rebuilder pressed the pulley on enough to align the belts but that was only about 1/2" onto the shaft.  The machine was on a test drive when the pulley originally came off.

 That would have been a handy piece of information to have when he asked me to take on the job.  I guess that is why he didn't tell me.  He knew I would never take a job like this if I knew up front what I was getting into.

Did I mention that the machine is torn down in a shop an hour away from my shop. 

Tuesday, May 3, 2016

Share your knowledge

Take the time to teach somebody something new today. I went out on a service call today. I met a young man who seemed very interested to learn about air-conditioning service. He was very interested in the air-conditioner that I was working on. He had a lot of questions about pressures and what was normal.

When I noticed that he had bought a set of gauges and a vacuum pump and was seeking knowledge to do the job, I took the time to answer his questions and went little beyond to give him some more information to learn. I also left him with my phone number so he could call me with questions after he experimented a little. I named a couple of professional organizations where he could go online for training also.

I think it's very important to teach the people who are going to someday replace us. Tech school is great, but I don't feel like it's the end of the line for learning or even necessary for everyone. Even after tech school a lot of graduates still need mentoring from us older techs.

Chances are good that you learned what you know from the experience of someone else. So why not pass it onto somebody younger with the drive to go on.