Hi all,

I have a small auto-pilot on my trolling motor and it stopped working last week. It would do everything except turn to port (left). I looked at the circuit board and Q9 transistor was totally fried (I wish I had taken a picture of it). I guessed that the transistor was an N-channel and ordered an IRFZ40 to replace it (decided on this based on the MOSFET driver that was near it on the circuit board MIC5016WM).

I started to replace the transistor this morning and realized that the pad for the Source leg, was completely missing (blown away!!!), so I took some pictures and need a hail Mary pass in the endzone for me to fix this circuit and figure out where I need to connect this leg.

Here are some pics of the board. I tried to re-attach the leg to a very small patch of copper that was attached to the pad (I found the missing pad) that can be seen near the crater that was missing in the board.

The transistors are isolated with small plastic bushings, except the transistor that melted, also melted the bushings on it's mounting bolt, so I mounted it using silicone. The plugs just to the left of the MOSFETS (labelled ORANGE and BLACK), drive the small hydraulic pump that turns the motor.

Thanks for any and all help, I now it's a long shot, but there has been no support for this board for several years and I haven't been able to find a replacement.
Don "AJ" Peacock

 

You came to the right place and met the guy for these kinda issues.

First take of the heat sink without damaging the board.
Next use alcohol and a bit hard bristle brush to clean the damaged area . A standard paint brush can be used by cutting the bristles a cm away from base. This way the bristles will feel hard to the touch. This way the board won't be scraped.
Take a good close up from both sides and show me.

Pictures need to be clear so I can look at what I wanna know

 

You came to the right place and met the guy for these kinda issues.

First take of the heat sink without damaging the board.
Next use alcohol and a bit hard bristle brush to clean the damaged area . A standard paint brush can be used by cutting the bristles a cm away from base. This way the bristles will feel hard to the touch. This way the board won't be scraped.
Take a good close up from both sides and show me.

Pictures need to be clear so I can look at what I wanna know

Will do, The photobucket pictures are much lower quality than my camera. Once I get good pictures, I can send you higher res versions.

Thanks a million,
Don

 

According to the patent the motor is in H Bridge mode , where are the other 2 Mosfets. It should be easy enough to just run a piece of wire directly from your mosfet , be careful not to bypass any current sensing or feedback in the output stage.Check polarity and whether drain or source etc
Patent attached here

Output stage on Page 6

 

Any idea why this fried in the first place?
Am I correct in thinking that there are 2 Mosfets on each side of the aluminium heatsink?

Any short in the pump motor should take out two sides of the H Bridge.

 

I see enough legs on that board to say there are 2 pairs of MOSFETs.

 

You came to the right place and met the guy for these kinda issues.

First take of the heat sink without damaging the board.
Next use alcohol and a bit hard bristle brush to clean the damaged area . A standard paint brush can be used by cutting the bristles a cm away from base. This way the bristles will feel hard to the touch. This way the board won't be scraped.
Take a good close up from both sides and show me.

Pictures need to be clear so I can look at what I wanna know

Hopefully these will help. I can work on better lighting etc. if you need more detail. Let me know if there is a specific view I can try to get.

You can see in the first photo, a piece of the board that was ripped upward when it blew out, then a crater!

You can see the piece of copper between the legs on the left in the second photo.
The blob of solder is where I tried to get it to stick to the copper. I can remove the blob and take more pictures if required.


Thanks again.

Thanks,
don

 

That 33 uf, 20 volt, surface mount, tantalum capacitor is also melted. Get one when you buy parts.

 

Now that the heat sink has been removed, it looks like that trace might go to the rightmost leg of the Q11 Transistor. I believe that is the source leg.

I know almost nothing about circuits at this level, would it make sense that the source of Q11 was attached to the source of Q9?

I was only guessing that this replacement transistor would be correct, based on the app note for the driver. Hopefully all N-channel mosfets have the same pin ordering.

Thanks again,

Do you like to fish? They are biting here and this issue is all that's keeping me off the water.

Thanks
Don

 

Any idea why this fried in the first place?
Am I correct in thinking that there are 2 Mosfets on each side of the aluminium heatsink?

Any short in the pump motor should take out two sides of the H Bridge.

Yes, The trolling motor failed and we tried using the autopilot/small motor as a rudder and use the main motor for power. The problem was that we changed course using the main motor, which caused the autopilot to go hard over and stay there (hydraulic pump continuous to one direction for extended time), I believe this is why it fried one side of circuit.

Thanks,
Don

 

According to the patent the motor is in H Bridge mode , where are the other 2 Mosfets. It should be easy enough to just run a piece of wire directly from your mosfet , be careful not to bypass any current sensing or feedback in the output stage.Check polarity and whether drain or source etc
Patent attached here

Output stage on Page 6

I really really appreciate your info, but that info is so far beyond my knowledge that I don't know what to say. I can run a jumper once we have a 'good guess' where I need to run it, but I can't check all the details that you mention.

The good news is that the hand control, switches, throttle etc. all work on the unit. The circuit can turn the motor to the right, but not to the left. So hopefully getting this MOSFET replaced and voila!

Thanks again,
Don

 

You can not trust 2 transistors to have the same pinouts. That's what datasheets are for...to tell you how it's built.

Right now, it's mechanical. Good eyes and a steady hand will get the parts installed.

 

U need better lighting.
How well do u know how to desolder double sided PCB's. ?

Using just one plain old gun will not help u in removing the mosfets without destroying the pcb and the vias.

It seems u have replaced them., If you are still having a problem then we need to look again.
If u wanna do this I can help u, this I guarantee. Ask around, members will say the same.

What u have is a DS PCB and is a bit difficult to deal with.

What I need u to do is to removes them for transistors. Mark which goes where if they have different no.s But as said before, if it is a H bridge then they should paired.

Post the no's on them tranny's. Remove the solder around the area completely. U need to use a temperature controllable iron with solder wick and some paste to clean that area so we can trace out what ends up where.

The best way is to clean the area up by removing all the solder in the hole and the surroundings

see the mobo pictures and get an idea what I am talking abt.

 

a) I know almost nothing about circuits at this level, would it make sense that the source of Q11 was attached to the source of Q9?

b)I was only guessing that this replacement transistor would be correct, based on the app note for the driver. Hopefully all N-channel mosfets have the same pin ordering.

a)=Yes but try and draw the H bridge section as shown in page 6 and satisfy yourself that this is the case.
I am nothing more than a middleaged clever motor mechanic. If I can reason out this kind of stuff and teach myself so can you.The internet didn't exist to help me either. It is by doing these kind of exercises that you learn about electronics (and never forget!) There is no better way to learn. "Give a man a fish and you feed him for a day- teach him how to fish and you feed him for life"
If you get stuck on the theory or need guidance there are loads of really helpful guys here who will guide you.

On a H Bridge circuit two transistors (Mosfets in your case) switch on together when applying power in 1 direction , for the opposite direction they switch off and the other two switch on.
I don't understand why only 1 output transistor is burnt both should have been carrying the same current.

b) Take #12's advice on this. Check the datasheets just in case, pinouts can vary (usually hidden in the seemingly irrelevant extra numbers on the component)
The main reason different different pinouts are used is to simplify assembly and track layout on a PCB

 

U need better lighting.
How well do u know how to desolder double sided PCB's. ?

Using just one plain old gun will not help u in removing the mosfets without destroying the pcb and the vias.

It seems u have replaced them., If you are still having a problem then we need to look again.
If u wanna do this I can help u, this I guarantee. Ask around, members will say the same.

What u have is a DS PCB and is a bit difficult to deal with.

What I need u to do is to removes them for transistors. Mark which goes where if they have different no.s But as said before, if it is a H bridge then they should paired.

Post the no's on them tranny's. Remove the solder around the area completely. U need to use a temperature controllable iron with solder wick and some paste to clean that area so we can trace out what ends up where.

The best way is to clean the area up by removing all the solder in the hole and the surroundings

see the mobo pictures and get an idea what I am talking abt.

I don't know anything about desoldering parts from a DS PCB.

I have a Hakko FX-888 with a small chisel point. I also have a cheap soldering pencil.

The transistors do not have any markings on them, just a small round melted mark (packaging/date code type mark??). I replaced the one transistor with a IRFZ40, based solely on the app notes associated with the driver. I can probably remove the transistors if you point me at some instruction to do so.

My gut feel is that if:
1) I've chosen a correct transistor.
2) I could attach the one leg to the blown up piece of copper.

It might work from there. I might have a line on another 'broken' board, but I don't know what issue it had. At least I'd be able to swipe one of it's transistors. I have no idea how long (if ever) I'll actually get another broken board.

Too bad you're not a neighbor, I'd let you fix the board and then we'd go catch some salmon

Thanks,
Don

 

I'm the next country neighbor. We need a freakin jet to visit.

Tell u what. first get some solder past and solder wick . remove the transistors and, completely remove the solder in and on tht area.

Show me the transistor ( a photo ) so we can make out the no.

And try or show me the other board if u have. We need to know the transistor type

 

I'm the next country neighbor. We need a freakin jet to visit.

Tell u what. first get some solder past and solder wick . remove the transistors and, completely remove the solder in and on tht area.

Show me the transistor ( a photo ) so we can make out the no.

And try or show me the other board if u have. We need to know the transistor type

There is NO marking on the transistors. The small packaging mark has the word MEXICO around the edge, with 2 digits in the center. One of them has a 46, one has 08 the other I cannot read. If there were markings on the transistors back in 1999, they are long gone.

Are you in Canada?Mexico?

Thanks,
Don

 

There is NO marking on the transistors. The small packaging mark has the word MEXICO around the edge, with 2 digits in the center. One of them has a 46, one has 08 the other I cannot read. If there were markings on the transistors back in 1999, they are long gone.

Can you give us the exact model and serial number of this autopilot and I will see if we can locate a service sheet somewhere. You are going to have to have the correct transistors or at least ones with matching characteristics.

 

Are you in Canada?Mexico?

Thanks,
Don

make a guess ?

 

Can you give us the exact model and serial number of this autopilot and I will see if we can locate a service sheet somewhere. You are going to have to have the correct transistors or at least ones with matching characteristics.

It's a Nautamatic TR-1 2000 autopilot. Purchased in Jan/2000.

Nautamatic was purchased by Garmin a couple years later. The current model is the Gold and is completely different with zero interchangeable parts.

This model has not been supported since sometime around 2002.

Thanks,
Don