Low battery warning on auto pilot

[Nostrodamus]

I have a Raytheon 6000+ head unit that all of a sudden won't engage the autopilot but just gives a low battery alarm.
This happened when we were under engine and I know I have full battery banks from testing and two readouts.
I have used a multimeter on all the suspect points and course computer and all give readings of 12.45 volts.
I have read that others have had the same fault and it could be down to the PCB board in the head (which of course they don't make any more).
Is there anything else I can test and does anyone know if the new autopilot heads are compatible with the autohelm 300 course computer or do I need one of those as well.
Thank you for any help, advice or replies.

 

[duncan99210]

If you're getting low voltage warnings but the battery voltage is fine, the first thing to check is the wiring to autopilot and the seatalk network. Any loose or corroded connections may cause a voltage drop which would cause the fault. Replacements are a coup,e of steps down the line, I think.

 

[macd]

+1 with duncan.
A multimeter will often not reveal the sort of working voltage drops duncan refers to, which can be critical to autopilot function.

 

[lpdsn]

+2.

Find some way of measuring the voltage under load. (I've considered fitting a cheap panel voltmeter and a switch).

In the meantime, you could inspect your wiring and connections.

Also, how thick is your cabling? I went for 6mm2 wire for my autopilot. I've been told I over did it, but I have no regrets and would do the same again.

 

[Nostrodamus]

You are all right and it is the first thing I checked. There appears to be no corrosion, the voltage along every line comes out right and there is no apparent drop. There was no intermittent fault and it worked well for years before the fault just appeared. I do tend to think it is the PCB board but I just don't know.
Searching of google shows a similar problem encountered by others and it turned out to be the PCB. Raytheon just say they don't make the board any more so there is nothing they can do and there is no way of over riding it. Just looks like I may be doing a lot of hand steering.

 

[markhomer]

Our auto helm starting turning itself off intermittantly , couldnt find what was doing it , turned out was a failing battery isolator switch which eventually went completely , once replaced auto pilot returned to norm , it was the only thing to be affected noticeably by the failing switch . Aparently not uncommon .

 

[Yngmar]

Both the ST50 (black, square buttons) and the ST60 (grey, round buttons) series control units will work with the type 300 autopilot, and both regularly appear on eBay UK. They're actually called ST6000/7000, but are often listed under the more familiar ST50/60 moniker. You should be able to get a replacement that way. Occasionally there's even new old stock ones, although those tend to fetch a high price.

Meanwhile, pop the unit you have open (fairly easy on ST60 series, no idea about ST50) and have a look for obvious reasons of failure, such as moisture traces and corrosion on the PCB and connectors.

 

[Nostrodamus]

Thank you all for your replies. At least I have some ideas to be checking.

 

[srm]

Had the same symptoms with my MK2 wheelpilot. Spent ages checking wiring and voltage drops without getting a clear diagnosis. However I noticed the motor housing was getting hot, to the extent it became too hot to touch shortly before the system stopped working.
Fitted a new motor and everything was back to normal.

 

[nigelmercier]

Put a 12V (or 24V) bulb in parallel with your meter when doing voltage checks. About 5W is fine, but not a LED.

Also note that the course computer has two power inlets, the high current one and SeaTalk.

 

[Nostrodamus]

I have not yet found anything obvious so I will just have to go through everything from the head unit all the way back to the batteries cleaning all the terminals and looking at the head unit. I understand that this system can be temperamental to voltage drops which can be caused by corrosion.
I thank everyone for their suggestions.

 

[Nostrodamus]

Now we are on shore power I have tested the connections to the back of the head unit and I am getting 13.94v when the head is on standby. When I turn on the autopilot there is no noticeable drop in voltage to to connecting cables but the low battery and warning signals sound stopping it going onto auto pilot.
There are two connecting cables going into the back of the head unit and I have tried disconnecting one and then the other but I am still getting the same. Would this suggest that the fault is probably in the head unit?

 

[nigelmercier]

Have you checked the voltage on the fat cables going into the course computer, not the head unit. See my post #10.

 

[Nostrodamus]

Sorry but I am no electronics or electrical expert so I am being pretty basic here and I hope those of you who understand these wire things can make sense of what I am saying.
I have good power to the control head with no noticeable drop when I switch from standby to auto. Auto or in effect the autopilot will not engage and "the low battery" and warning buzzer comes on.
The main power feed into the autopilot black box (the brains) are showing 13.56 volts with no drop when switching to auto. There is however no power going to the autopilot linear drive ( This may be expected because the drive and autopilot is designed to cut out and go to standby with low power).
I have taken the head unit off and opened it up and there is no sign of moisture or corrosion.
My feeling is that the control head has developed a fault or the capacitors are gone.

 

[nigelmercier]

The main power feed into the autopilot black box... My feeling is that the control head has developed a fault or the capacitors are gone.

Sorry to keep on, but have you checked both power feeds to the "black box"?

Capacitors?

 

[superheat6k]

This happened to my type 100 recently.

There is a diode on the board that fails on pre 1997 units.

This fixed it ...

https://www.dropbox.com/s/cdlabidtequ88jt/Autohelm 100 Low Voltage Fault resolve.pdf?dl=0

The diode is as cheap as chips from Maplins.

 

[Nostrodamus]

Superheat 6K... as my model falls within these units this could well be the problem and all the same signs are exhibited.

Technical Update ISSUE NO: PAGE 2 OF 3 DATE: TU 016 06/06/97 It has come to our attention that a number of course computers have been failing due to excessive power dissipation in diode D25. This problem can easily be recognised by seeing the ‘LOW BATTERY’ alarm when the pilot is in Auto mode and the absence of clutch and motor drive. It is possible that any of these course computers may suffer from this problem but is most likely on units with serial numbers later than 0370001. A short term fix will be implemented on the PCB where a 1N4001 (or better) diode will be soldered to the rear of the PCB between one of the legs of relay RL2 and the negative end of capacitor C18 as shown in the diagram. Note, the cathode (bar end) of the diode should be connected to C18....

I have tried everything else.

 

[Nostrodamus]

Nigel, yes, I have tried both power feeds. None show any drop and when switching to the auto mode the power (big and little feeds) is the same going in but nothing is going to the linear motor and it wont engage (just the low battery warning).

 

[prv]

Superheat 6K... as my model falls within these units this could well be the problem and all the same signs are exhibited.

Well, this sounds pretty conclusively like your answer. Time to break out the soldering iron. Should be an easy fix.

Pete

 

[nigelmercier]

... The diode is as cheap as chips from Maplins.

Well done for the fix, but Maplin (spit)? 49p each!

http://r.ebay.com/EiB30H 10 for 99p, including postage.

Or CPC for the real price, 3p each.