8970 repair

[Bern]

I'm working on an 8970 right now. Tractor wouldn't move at all. Dealer came out, did some testing, and quoted him a 20K for a reman transmission, not including labor. He asked me to look at it. Found faulty shifter unit, $120 repair at Ag Express. Told him I should charge him 19K for labor and he'd still be ahead!

Right now I'm fixing an issue with the fuel shutoff solenoid (recently replaced by someone else). Problem turned out to be weak batteries and corroded cables. Simple fix. See attached video link.

Scope allows me to see things that I can't with a conventional voltmeter. It's an invaluable tool for some things. The actual problem occurred for about half a second.

Legend for video:

Blue = pull-in coil current
Green = pull-in coil voltage
Purple = hold coil voltage
Red = battery voltage
Video

 

[Tom in Mo.]

Isn't that terrible. It rolls my stomach when I hear a dealer service story like this. A lot of owners bite the bait too.

 

[Bern]

That's why they're called stealerships. As I tell my students, I'm not training them to be parts
replacers, but rather techs who can think for themselves and troubleshoot a problem logically and
accurately the first time.

I can't even imagine the amount of word twisting and story fabrication that would have been required if
this dealer had replaced the transmission and racked up a 30K bill, only to discover the same problem
they started with when they got it all back together.

The actual problem was a faulty *clock circuit* in the printed circuit board in the shifter unit. I
didn't even know those boards used something like that. The transmission shifter uses a single magnet to
do all of the shifting. Pretty interesting technology for a machine nearly 30 years old.

 

[chevytaHOE5674]

Being able to work thru a problem and do some diagnostic work to get to the root is not a skill everyone has. A service manual and going thru the troubleshooting steps and understanding the theory of operation goes a long way in fixing problems.

 

[Sean in PA]

The actual problem was a faulty *clock circuit* in the rinted circuit board in the shifter unit. I didn't even know those boards used something like that.

If it has an integrated circuit (chip) of any kind to control things, then the chip generally needs a clock source, which is basically a timed pulse that tells the chip to proceed on to the next step in its logic.

 

[mrhud]

(quoted from post at 08:06:50 03/11/23)

The actual problem was a faulty *clock circuit* in the rinted circuit board in the shifter unit. I didn't even know those boards used something like that.

If it has an integrated circuit (chip) of any kind to control things, then the chip generally needs a clock source, which is basically a timed pulse that tells the chip to proceed on to the next step in its logic.

how many channel is that scope ? was going to just get it with the new autel, or can you get a scope with the texa ag industrial

 

[Bern]

4 channel, they make up to 8 but have never needed more than 4. It's called a PicoScope and I would not be
without it for high-tech diagnostics. Yes, I likely could have figured out that start solenoid issue with
maybe a test light, but the Pico makes it so much faster and certain.

The nice thing about the Pico is that it interfaces with a laptop. Screen size is important to me, as I
have no desire to analyze waveforms on a little 4x4 screen.

Link below.
PicoScope

 

[mrhud]

ihave a 4 channel with my old otc scan tool and i am not very good with it because you do need to know what you are looking at, i just dont seem to use it regular. like use my fluke 88 . i have been told not to get the autel one when we get a new scanner and buy the pico thanks for the info

 

[Bern]

I've used some old scopes in the past that are downright painful to use. The Pico software makes it so much
easier that it has become a tool that I'm more likely to use than my Fluke 87 meter in some cases.