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Old 07-12-2009, 12:07   #1
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Autopilot Computer Repair

Ok, my Navman G-Pilot computer is acting up. They don't repair, only replace the computer unit.

The particular problem is no 12V high amp output to the hydraulic pump. On opening up the computer case, I discovered 4 MOSFETs that appear to control the circuit traces to the pump output. Since the rest of the system including the solenoid seems to be working ok, I have decided to try to take a shot at repairing it rather than paying hundreds of dollars for a new computer or thousands of dollars for a new system.

I have subsequently identified and ordered replacement MOSFETs. It appears to be a simple transistor replacement soldering job. I don't know for sure if this is the problem, but for a few dollars, what can I lose.

Out of curiosity has anybody ever done something like this?

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Old 07-12-2009, 12:30   #2
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I replaced a potentiometer on my auto pilot once it worked well for awhile but the AP is almost 25 years old and I keep having troubles with it so am currently in search of a new AP. Good luck I hope it works for you.

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Old 07-12-2009, 12:38   #3
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Any idea why the mofsets went out?

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Old 07-12-2009, 12:47   #4
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G'Day Mate,

Can't help you with specific info, but as a fellow G-Pilot owner I am surely interested in how it works for you.
Please post your results!!

We've had ours for about 4 years now, and perhaps 25K miles of use, and in general we're happy with the way it steers our boat... not an inconsiderable task, because it is a fairly twitchy almost ULDB "performance cruiser", and requires a lot of steering.

But, the display head on ours has been a PITA. A few of the LCD segments failed while it was still under waranty, so we sent it in... they claimed to have replaced the display, but within a few weeks (by which time we were offshore and unable to interact with NavMan), it began to fail again. By the time we returned to Oz, it was out of waranty, and I have been reluctant to pay for a repair that would quite possibly not be permannent!

But, enough of my whining. I hope that your FET replacement is successful, and we will be very interested in how it turns out.

Jim and Ann
s/v Insatiable back in MBTBC marina, waiting for next eye jobs to be done
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Old 07-12-2009, 14:16   #5
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Some of my segments have failed as well. Hopefully that has nothing to do with my current problem and it is the MOSFETs.

I have no idea why they failed, if they actually failed. I am not aware of any lightning strikes while using the autopilot or any other problem that might have caused them to fail.
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Old 07-12-2009, 15:18   #6
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I had an intermittent problem with my Autohelm AP. I posted a thread about it on Cruisers Forum. The problem wasn't bad Mosfets, just the circuit board connections to them. Heating and cooling had caused microscopic cracks on 9 out of 12 connections.
Try resoldering them first.
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Old 07-12-2009, 15:32   #7
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I've had a few MOSFETS blow up on protoboards, but it's rare to see them self-destruct in a production circuit. Steve B.'s comment about micro-cracking in the circuit board traces (or the solder joints themselves) is one that crops up all the time, in all sorts of devices. Sometimes it's just a matter of de-soldering the joints, cleaning them with fresh flux, and soldering them back together. If a trace on the board itself is cracked, it's often possible to replace it with a short wire.

Best of luck with the repair. And as for dead LCD segments- I've never tried to rebuild an autopilot head, but have had multimeters do the same thing. Disconnecting and cleaning the connector to the LCD (sometimes they're just a spring fit against a pad on the circuit board) often solves the issue. The LCD itself has little that can go wrong, except for the inner layers getting crushed by an impact.
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Old 09-12-2009, 10:59   #8
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No Joy

I performed conductivity checks between all the MOSFETs and their traces. There were no problems.

I then removed and resoldered the replacement MOSFETs to the board. Same situation as before.

Rather than putting more money into a system that isn't being manufactured anymore, I suppose the wise thing would be to go to another brand.

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