MotorGuide Intermittent Power Loss

[naneely]

I'm new to this forum, but I'm optimistic that someone will be able to give me some help. My MG Brute Competition 765 with 55# Whisper 24V motor began losing power recently. When under full load it will start off normally, run for 10-30 seconds (or more), instantly shift to slower speed for a while, then back again. If I cycle the power on and off sometimes it starts off normally and sometimes it starts off on the slower speed. My guess is that the brushes could be bad, but I don't want to break into the motor only to find something else is wrong and have the buy seals, etc. for the motor for nothing.

Can anyone offer me a good method to diagnose this problem or, better yet, a good diagnosis?

Thanks,
naneely

 

[wire2]

Re: MotorGuide Intermittent Power Loss

Is it controlled by a foot switch? Problem could be in that. If you can get test leads on the motor wires, see if the voltage to it varies. If not, it's in the motor.

 

[naneely]

Re: MotorGuide Intermittent Power Loss

Thanks for the reply wire2. It has a foot controller with 3 settings; (1) continuous on, (2) switch activated on tied to the variable speed controller, and (3) switch activated on for only high speed. On any of these settings it still has the problem I described. If the foot control is a problem, does this help diagnose the problem as related to the motor or is there something specific you think I could check on the foot control?

I've also checked to make sure all of the wires on the foot control and under the top cover of the trolling motor and all are snug.

I'll try to get a voltage reading on the wires leading to the motor as you suggest. Thanks again for your guidance.

Thanks,
naneely

 

[wire2]

Re: MotorGuide Intermittent Power Loss

One other thing you you can check for; where there's resistance, there's heat.
When it starts to act up, place your hand over all the places where wires enter/exit. If it feels warm, there's power being lost there.
Do any of the wires plug in? Any corrosion on any pins/sockets?

 

[naneely]

Re: MotorGuide Intermittent Power Loss

I called the service center today. The immediate response was that the "mosfet" was bad and there aren't any more available. I get the story that I can upgrade my unit to a digital unit with higher thrust for about $450, which is not a very attractive option on a 12+ year old unit.

I read a somewhat dated string of messages from "K-dog" that is very interesting (address below) at the address http://www.wmi.org/bassfish/bassboard/boats_motors/t77809.htm. The message reads...

"...The mosfets are very repairable. The transistors themselves run about 20 bucks. I am talking about the ones in the foot. The ones I fixed were all dura amp models. You hold the brushes back while removing the armature. You remove the wires from the head and pull thru the motor shaft. I replace all the seals when I take the foot apart including the two small ones that hold the heatsink in place for the mosfet board. The 20 dollars is for the transistors, plus another 22 for the motor seals. NOT including labor. It takes less then 2 hours to finish the job. You need to desolder the old transistors and solder new ones on without ruining them. Fosters- anything electronic can be fixed if your willing to look for the parts. The 1991 motor I fixed took me hours of cross referencing to find parts for thru Newark. Anybody who is into electronics and is even remotely knowlegable can fix these. The speed control circuit is actual not that difficult. Electronics is just like everything else. If you take them in to be fixed, most places just want to sell you a new or upgraded board {no offense Foster's} but like I said, anybody worth a darn at electronics fix these. K-dog"

Does anyone know exactly how to identify what mosfet to buy from Newark and if this repair is a realistic option? Is anyone aware of a detailed description and/or set of pictures to describe exactly how to perform this mosfet fix? Does anyone offer a remanufactured version?

Thanks,
naneely

 

[wire2]

Re: MotorGuide Intermittent Power Loss

Open it up, there will be a number on the transistors. Post it here, someone will find them. $20 sounds high but we'll see.

Mosfets are static sensitive, use precautions handling them. Unsolder with a pneumatic sucker, put heat sink compound on the new ones.

 

[naneely]

Re: MotorGuide Intermittent Power Loss

I took your advice wire2; I broke into the motor this evening and found the electronic parts that are supposedly failing. I'll post the details here, but probably will post another separate item with a more distinct title to help get more attention on my need to find 2 replacement electronic parts (mosfet).

I found two of the following components: (I believe these are mosfet)
IRF Z44
I R4049
5L 3C

I found one of the following components: (Is this a mosfet, too?)
9040
->|<- MUR
3005 PT
(also stamped with a Motorola symbol and a "France" label)

I found a part that looks very similar to the first part above at the following site,
http://www.mcminone.com/product.asp?catalog_name=MCMProducts&product_id=IRFZ44

Does anyone have any idea exactly where I can find these replacement parts and exactly what to ask for to ensure that I get what I need?

Thanks