Trying to understand an old Autopilot pump motor...

[MikeP]

My original 1980 Raytheon Neco AP quit working a few months back, the day before I left the boat. Now I'm back and am troubleshooting. The pump hydraulic solenoids activate properly. But the pump motor no longer activates when rudder is called for. The DC motor is different than what I am familiar with.

Instead of two terminals, it has four. One pair currently has 32V applied when the AP is on. This pair of wires runs from the terminal block on the motor to the motor windings. The other pair goes to the brushes and 32V is not applied at any time with the AP on and rudder called for.

DC motors that I am familiar with have only two terminals, a + and - So I do not understand the function of the terminals that connect directly to the windings. It SEEMS to me that the problem is in the controller, not the motor, because I would expect 32V to be sent to the brushes, + to one brush, - to the other, but at the moment 32V never appears at the brush terminals. I want to understand how, exactly, this motor works so I can better figure out what's going on (or not going on).

The AP has worked flawlessly for years and the motor just suddenly quit. I checked all connections/terminal blocks and they are OK. There is a control box with a variety of electronic components but it will require disconnecting about 30 wires from small terminal blocks to be able to open it. But I want to understand what the purpose of the 4 motor terminals are. Any ideas?

 

[MikeP]

Think I've figured out the motor terminal issue - The pump motor its a motor with "separately excited field windings, - a "sepex" motor (just learned that term)! So there is, in this case, battery voltage applied separately to the field coils. So that part is working fine.

I disassembled the control box and have been troubleshooting and have found a transistor that does not appear to test properly however I have not removed it from the circuit so I can't say for sure if it's bad yet. There is a separate master solenoid in the box that supplies the power to the brushes and that solenoid is not triggering. THe transistor in question is part of the control circuit for that solenoid. All other components in the circuit box test OK - diodes, power resistors, regular resistors. This transistor seems to be the only suspect at the moment...

 

[Bill Herrin]

It's been 30 years since I trouble shot a Neco autopilot and my memory has gone to hell due to age. If my assumption that you don't have a manual and can't find one on the net is correct the first thing I'd do is figure out what the pump needs to run in both directions (I don't recall the actual control of direction with Necos being done with electro-hydraulic valves and a one direction pump but I could be wrong, I know we installed more than a few of them with the old Benmar 16B pumps assemblies because they were bullet proof)... it has to be able to push the rudders port and starboard. With that knowledge and knowing that in fact the pump can do that I'd look at the control circuitry to see what it's going to take to get the left and right signal from the pilot working with the power pak.

British electronic engineering is always a little obtuse!

Good luck

btw, in those days and in my opinion those Neco's and Wagners were about as good a match for your boat as there was.... It's be worth the effort to get it working well.

 

[MikeP]

Thanks Bill. Yes, the old NECO AP has been superb so I want to fix it...

I just discovered that the transistor in the motor control box, a 2N2646, is defective. Since it is part of the circuit that controls voltage to the electronic solenoid that sends power to the motor brushes, it appears that is the problem.

I ran to Radio Shack, hoping that since it's a very common transistor, they might have one. Yeah, sure! They did have a nice selection of new cellphones.

So I'll order a transistor - the shipping is more than the transistor. Oh well, I did the same when I rebuilt my searchlight's voltage board - a .69 diode was the fix. This time it's a relatively expensive part, almost 3 bucks!

 

[MikeP]

Transistor - $2.78
Shipping - $11.06

 

[Boatnut]

Transistor - $2.78
Shipping - $11.06

Sounds like that is overnight or 2nd day, if not maybe there is handling charges. Are you being patient or in a hurry? LOL Shipping costs have gone nuts, but geeeez, I hope 11.06 is for priority.

 

[MikeP]

Nope - "normal" shipping - whatever that is going to be. I figure they
re making money by charging silly "packing charges" as opposed to dropping the transistor in a padded envelope.

It's cases like these where I miss the old days of corner electronic shops where you could just walk in and buy stuff like that.

Oh well, if the transistor is defective as testing indicates, it's still a cheap fix.

 

[Bill Herrin]

That sounds encouraging Mike, the way things are going with electronics I suppose we're lucky to be able to buy components at all... even if it is on the net and no longer at local retail stores.

When I started my first marine electronics shop we used to get a lot of transistors and components at radio shack because it was quicker than waiting for stuff from the manufacturers, you're right, now all they have there is finished goods and not very good ones at that. I suppose it's the same at hardware stores that stock more washing machines than hard to find hardware items.
I hope that fixes it for you, let us know...

Bill

 

[Boatnut]

Mike, consider yourself lucky, I have parts shipped to me all over the place, that transistor would run about $100 to ship here in Jamaica, plus 200 percent duty. You should hear them whine when I have to have parts sent in. They don't have a lot of choice as the parts are for medical equipment. Priority overnight, typically takes 4 or 5 days, due to customs, not to mention the Jamaicans who are wonderful people, have no concept of hurry unless they are behind the wheel of then get out of their way.

 

[Boatsb]

Nope - "normal" shipping - whatever that is going to be. I figure they
re making money by charging silly "packing charges" as opposed to dropping the transistor in a padded envelope.

It's cases like these where I miss the old days of corner electronic shops where you could just walk in and buy stuff like that.

Oh well, if the transistor is defective as testing indicates, it's still a cheap fix.

get real. Do you think the part is profitable enough at under $3 to constitute a reason to stay in business?
Om
Shipping and handling is usually there to cover the cost of shipping and handling.

 

[MikeP]

"Mike, consider yourself lucky, I have parts shipped to me all over the place, that transistor would run about $100 to ship here in Jamaica, plus 200 percent duty"

Wow, glad I'm not in Jamaica. Sounds like even boatsb might find that excessive!

 

[Beckytek]

You should have ordered 2, just in case the problem is somewhere else and blows the new one.
I've worked on a lot of equipment containing solenoids and the driver transistor usually blows when the solenoid coil shorts. Check that coil before you change the transistor or it may blow again. Ron

 

[MikeP]

Thanks Ron, I'll do that. Coil resistance is 49 Ohms - I have no idea if that's within the spec for the coil but it sounds reasonable but I'll check it for operation by directly connecting some power to the solenoid itself before soldering in the new transistor.

 

[Beckytek]

49 ohms sounds good. There should be a diode in that circuit also. If the diode is open it will cause the driver to go bad. Hopefully it was just a tired transistor.

 

[MikeP]

Diodes all checked out OK!

 

[MikeP]

Received the transistor(s) today.

Soldered in a new one and Voila! Autopilot functioning normally now. WHEW! I'm sure as heck glad I didn't have to have to spend 3k USD to replace it with a new one.

 

[Beckytek]

Makes you feel good doesn't it?

 

[MikeP]

Yep, I'm a HAPPY GUY!

Almost wish I hadn't quit drinking, this would definitely call for several!

 

[jim rosenthal]

Ummm... congrats!! have a Dr Pepper, almost as good as rum.......

 

[SeaEric]

My new Garmin was $4K + another $2K for install. It works great and I'm very happy with it - but your deal is better, even with shipping!