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Old 06-08-2011, 07:45   #1
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Diode Autohelm

Long shot. My auto pilot head end frizzed. I am looking at new stuff. I have been going accross the circuit board looking for a bad spot. I bench tested the relays they fire and make up. Pretty fine work I think i did that well. There is a diode at the clutch relay that I do not have continuity accross. Here is the dumb question can I test continuity accross a diode using a fluke set on ohm meter? Lovely if all I needed was to solder in a diode.ray no longer services this unit. Probably get a new one but now I'm being stubborn
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Old 06-08-2011, 08:11   #2
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Quote:
Originally Posted by sabray
Long shot. My auto pilot head end frizzed. I am looking at new stuff. I have been going accross the circuit board looking for a bad spot. I bench tested the relays they fire and make up. Pretty fine work I think i did that well. There is a diode at the clutch relay that I do not have continuity accross. Here is the dumb question can I test continuity accross a diode using a fluke set on ohm meter? Lovely if all I needed was to solder in a diode.ray no longer services this unit. Probably get a new one but now I'm being stubborn
Yes. That diode should test with a Fluke set on Ohms or Diode test. A diode at a relay is commonly there to suppress the voltage spike which occurs when the circuit opens. Is the diode in parallel with the relay coil or the contacts? It will be installed in the reverse direction.
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Old 06-08-2011, 08:24   #3
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Quote:
Originally Posted by daddle

Yes. That diode should test with a Fluke set on Ohms or Diode test. A diode at a relay is commonly there to suppress the voltage spike which occurs when the circuit opens. Is the diode in parallel with the relay coil or the contacts? It will be installed in the reverse direction.
thanks saddle
I think it's reverse direction but I need to check. It may be a symptom of another issue. The thing was working pretty hard in a nasty sea and has served it's life. Can't hurt to try a new diode. The only other point on the board that had discoloration was one of the heat sinks. Would a diode fail over time if it were being used hard or often. Again no complaints this thing has done well and many many hours. If this doesn't work it will get a proper respectful ceremony.
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Old 06-08-2011, 08:25   #4
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Re: Diode Autohelm

If you are trying to test a diode that is on a circuit board or otherwise connected to other components, then you should disconnect one end of the diode. On a circuit board you can unsolder one end of the diode and lift it off the board. Make sure that you first disconnect all power going to the circuit before you disconnect the diode. Then measure the diode resistance both ways. One way the meter should indicate an open circuit. The other way you should get a reading (often a reading around 600). That indicates the diode is good. If you measure an open circuit both ways, the diode is open. If you measure low resistance both ways, the diode is shorted.
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Old 06-08-2011, 08:34   #5
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Re: Diode Autohelm

The diode at the clutch relay would only see duty when the clutch was released. However the failure of that diode might, depending on how it is being used, cause failure of the driver semiconductors. Does the clutch work?

The clutch and motor can usually be tested directly on 12v power to determine if the problem is with the controller or the actuator.
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Old 06-08-2011, 08:36   #6
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Thanks Gord I will pull the diode. The board is disconnected and on the dinner table uhhhh salon.my iPhone likes to spell things for me so gord often becomes ford and Daddle is actually saddle. I'm trying to compensate. Thanks again this forum has been very helpful troubleshooting.
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Old 09-09-2011, 08:16   #7
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Re: Diode Autohelm

Hi
Did you succed with your diode testing. I have the same problem so i would like to hear your result.
kind regards
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Old 09-09-2011, 18:01   #8
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No joy. I really think the problem is at the circuit board connections to the drive power. I have not had time as of late to sit and solder into the board. Takes the right mindset. Ray is suggesting I buy a rebuilt x-30. Now weekend sailing I can deal with balancing the helm and hope I get motivated to to look and solder some more.hope you have some luck.
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Old 09-09-2011, 18:12   #9
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Re: Diode Autohelm

which model autohelm?
believe it or not i actually pryed a couple schematics out of
autohelm before they became raymarine.

there should be a small diode symbol on one of the ohm scales on your fluke.
(it is the 2K scale on mine). On this scale the fluke will generate sufficient
voltage (> .6V) to cause a diode to go into forward conduction. On the low
ohm scales often the voltage is insufficient to test the diode.

cheers

gello
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Old 11-09-2011, 11:41   #10
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Re: Diode Autohelm

Hi gello
My system is a autohelm ST 7000 system.
And my main problem is that, when I push the “standby” button on the display, the power remains on the clutch. So I have shut down the power on the hold system, to get free wheel steering .
I believe there is a “switch diode” error, some where on the main board.
So an Circuit Diagram on a ST 7000 curse computer would reallyhelp, but any kind of help or input are welcome
Kind regards
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Old 13-09-2011, 08:23   #11
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Re: Diode Autohelm

in response to some private messages,
the schematics i have are for a 6000 autopilot.
i posted them for download on the web at
http://www.baldriver.com/repository

as to the autohelm issue.
pardon me for being basic

I am assuming when you kill power to the unit the clutch releases. (true?)

when the unit is on, clutch engaged, and you hit standby,
does the unit continue to try and steer or does it quit
steering but leave the clutch locked? (trying to ascertain
control unit versus interface).

does your main unit have a row of large transistors
in silver cans or with metal tabs on a heat sink? if so, how many of them are there (should be 0, 4, or 5 depending on the computer.).

(looking for the clutch control transisitor unless for some
odd reason raymarine went back to the expense and reliability
issues of relays in their new units.).

gello
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Old 13-09-2011, 11:58   #12
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Re: Diode Autohelm

Hi gello
Thanks your for respons.
When i cut the power, on the main wire, the chucht release the wheel styring, so it's not steering engine that is problem.
But i have take the computer a part, their is a switch diode on the lower part of the circiut board, (Name: BDW94W) that i believe is the problem. Do you now any thing about this part.
My main unit have 5 large transistors on the outside, but if one of them is related to
the chucht, which one is't then ?
(Sorry if you find my english bad, i'm from denmark)
Kind regards
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Old 13-09-2011, 17:46   #13
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Re: Diode Autohelm

BDW94 is a transistor and yes, it is part of the clutch circuit. Remove it and you can test it with a diode tester or better yet, just replace it.
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Old 13-09-2011, 20:27   #14
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Re: Diode Autohelm

Quote:
Originally Posted by Capn Dan View Post
BDW94 is a transistor and yes, it is part of the clutch circuit. Remove it and you can test it with a diode tester or better yet, just replace it.
Capn Dan, i will take your word for it that it is part of the clutch circuit.
i don't have a schematic for the ST7000. thanks for the info.

If there are five heat sinked transisitors chances are that 4 of them
control motor for the ram and the fifth one is possibly the main driver
for the clutch. I was going to suggest he ohm out the clutch
wire to the collector and emitter (or possibly Drain and source)
of each of the power transistors to see if one is the
control for the clutch. If the BDW94 is only diode sized could it be the
driver for the power transistor for the clutch? If you have anymore
documentation it would be appreciated. Fixing a board remotely
with no schematic and no hands on is tough. My fear in replacing the transistor is that if it is a pre stage to the main driver it will just blow
again instantly if the final driver is shorted.

I have jury rigged a surprising number of them at sea for people but
i carry necessary parts, a scope, and instruments so this way is like shooting in the dark.

whatcha think?

can you read the numbers on the power transistors?

g
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Old 13-09-2011, 20:57   #15
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Re: Diode Autohelm

I do not think that the power amp board has anything to do with the clutch drive other than the 12/24 volt power passes first through the PA board and then back to the computer board.

I believe that the fifth power transistor on Kastrup's computer is part of the 24 volt circuitry and would reduce the 24 to 12 volt for the computer board and control head. The 5th power transistor is not seen on the 12 volt versions.

The power transistors are MJ11029 and MJ11028 / 50 amp.
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