M1078 A1: No power to WTEC III

[SpaceGhost]

Hi all,

I purchased a M1078 A1 in October of last year. I drove her from Western Washington to Northern Idaho on the Montana boarder with no issues. During the winter, I started her every two weeks and got up to operating temperature (to the point the fan turned on). A few weeks ago, when I went to move the truck for the first time since parking for the winter, I fell victim to the dreaded "no start" issue. Actually, it started up fine, but then once it came up to temperature, I noticed "Check Trans" was illuminated and the transmission control panel was not illuminated. Not knowing the significance of this, I figured I would just restart the truck, but as many of you know (and I have come to find out) if the "Check Trans" is illuminated, power is cut off to the ignition switch.

I used the troubleshooting guide on Transmission Instrument's website and thought I diagnosed the problem to the WTEC III ECU, so I sent them the WTEC III and control panel to to diagnose/fix; however, both checked out fine. John with Transmission Instruments noted that the error code indicated that the WTEC III lost power while the engine was running. He recommended that I clean any oxidation in the power lines starting with the battery box. I cleaned all the terminals and connections in both the battery box and the main cutoff switch area, but still have the "Check Trans" light on. I rechecked the WTEC III again, and test lam would still dimly light up when checking the battery ground and power on the grey connector (pins #17, #32 and #16, #17, respectively). I rechecked the ignition power (grey connector #17 to black connector #4) and got a bright light. However when I rechecked the battery ground and power on the grey connector, the test light did not illuminate... It seems like it's a break in the wire somewhere. I check the back of the power distribution panel (PDP) and found no loose connections. I currently have no voltage at the CB79 fuse, and I'm not sure what my next step should be.

Incidentally, the LD2 and LD3 lights on my PDP are illuminated. I tried looking up the significance of this, but could not find anything. I included an image of my PDP because I realize there are a few different ones out there.

Hopefully this makes sense and someone can point me towards what I should be checking next.

Thank you!

 

[Skyhawk13205]

Check your 24v ignition bolt on your PDP panel to GND with the master power on. You should have 24V also the 24v ignition led should be on.

 

[SpaceGhost]

Skyhawk,

Now that I look at the PDP again, I bet the LD2 is for 24v ignition and LD3 is for 12v ignition, since they are located right next to those bolts. Both of those lights come on when the ignition switch is applied, and I get ~24 and ~12 volts from each, respectively.

 

[Skyhawk13205]

check pin 4 on the ECU black connector to CB79 with a ohm meter. You should have continuity.

if you don’t check with connector for pushed pins and check your fuse as well.

 

[Ronmar]

Yea, trans power starts at CB79 once the main sw is on. I would also measure the voltage at the PDP test points as you turn things on. A bad connection at the LBCD or a bad ground could be killing your voltage under load.

 

[Suprman]

The pcb power panels can develop bad solder joints. I have pulled relay sockets right out of the boards.

 

[SpaceGhost]

Thanks everyone for your replies and help! It's the PDP. I had someone come out to help diagnose the issue, and we found out that when we pressed on the PDP on the J302 bank above the relays we would get some voltage and the transmission control panel would flicker. So now the question is to try to source a working PDP or try and reflow the solder joints to see if that works. I've reflowed solder joints before on an old arcade system to bring it back to life, but this board has some kind of silicone coating on it that I'm not familiar with. Has anyone reflowed the connections with success, and do you have any tips?

Thank you!

 

[Suprman]

I have new pdps. Not cheap though. It’s soldered on both sides. I have heard of them being resoldered.

 

[Ronmar]

Thanks everyone for your replies and help! It's the PDP. I had someone come out to help diagnose the issue, and we found out that when we pressed on the PDP on the J302 bank above the relays we would get some voltage and the transmission control panel would flicker. So now the question is to try to source a working PDP or try and reflow the solder joints to see if that works. I've reflowed solder joints before on an old arcade system to bring it back to life, but this board has some kind of silicone coating on it that I'm not familiar with. Has anyone reflowed the connections with success, and do you have any tips?

Thank you!

You should be able to warm the coating to remove it. I have placed potted assemblies in near to boiling hot water before to soften the sealant/potting compound for easy removal. You only need about 200F or so, which is not enough heat to damage anything else on the circuit board. Then you can re-flow the solder joints.

About the only risk you run is using too much heat while re-soldering which can damage active components like transistors and diodes. the way you protect them is to control the heat and duration, and or connect a heat sync to the lead being soldered, right where it enters the component body. I typically use a small pair of hemostats clipped to the component lead right where it enters the component body, while I solder the tip of the lead where it protrudes from the other side of the circuit Board. Like sweating copper pipe fittings together, The solder will melt and flow along thru the circuit board from where the heat is applied till it reaches the heat-sync… with proper heat in the iron, it should take you no more than about 5 seconds to see the solder melt on the opposite side of the circuit board from where the iron is applied. Lotsa youtube vids on circuit soldering.

You can probably find an old scrap appliance(dishwasher or washer/dryer maybe, something with several panel buttons and indicator LED’s) and pull a soldered circuit board out of that to practice on. If you ask at the local garbage dump, they may even let you pull one out of an old appliance from their scrap metal recycle pile before it is sent off to be melted down.

in the end, yours is broke, you can’t break it any worse, so you loose nothing but a little time by trying

 

[SpaceGhost]

Thank you all for your help!! Delayed response because I was in the process of moving, but I did get her running.

I ended up re-soldering all the connections in banks J302 and J303. I found it easiest to use a brass brush to remove the silicone coating to get to the joints.

Unfortunately, solder joints weren’t the problem. After much consternation, I pulled the fuses for the third time and looked at them very closely… There was a hairline crack right at the corner of the fuse on CB43 (if I recall correctly), and it was difficult to see without magnification. Replaced the fuse, and she started right up. Wish I had just swapped the fuses to begin with… lesson learned. What threw me off was the intermittent power that I had for a while. I’ve never dealt with a fuse that only partially went out.

 

[DieselAddict]

A quick troubleshooting tip that I use is to go through the fusebox with a VOM and check for voltage on both sides of the fuse. It can save you a TON of trouble with that exact problem. It only take a few minutes and eliminates a lot of real estate in one sweep.

 

[SpaceGhost]

A quick troubleshooting tip that I use is to go through the fusebox with a VOM and check for voltage on both sides of the fuse. It can save you a TON of trouble with that exact problem. It only take a few minutes and eliminates a lot of real estate in one sweep.

That's a great point! One reason I don't feel too bad about all the extra work is that both I and a technician who came out to look at it did just that. It was such a small crack that the pressure from the volt meter test leads must have been enough to cause the connection to bridge. He also advised that it was probably a bad solder joint.

 

[DieselAddict]

I just ran across something very similar. A friend called to help them figure out a problem with a power outlet in their home. It showed voltage but nothing plugged into it would run. Came over and tested it with the VOM and sure enough, had voltage across the terminals but as soon as you plugged something in and turned it on you got nadda. Turned out the HOT lead behind the outlet was broken but it was broken far enough up the insulation that it held together and had enough contact to show voltage but the joint wouldn't pass any real current.

The crazy things you find when working to solve problems. Glad you got it sorted.