faultfinding atillerpilot with multi meter

[steve yates]

My tiller pilot, simrap tp-10, was playing up, intermittently at first, coming back with a wiggle of the wire, then giving up entirely. when I opened up the plug the blue cable was had pulled out from its connecting pin. While taking it apart I forgot which cable had gone to which pin (duh)
I have reconnected them both ways around, but on plugging into the socket aboard there is nothing from it whatsoever.
What tests should i run with my multimeter (total novice with one) to check whats what with the plug/cable on the tp and the socket on the boat?
Also, how do I know which pin to wire the pos and neg to? I have kind of assumed that with the fat pin up (unused) the blue goes to bottom left and the brown to bottom right pin, is there a way to use the multimeter to check the polarity of the matching socket holes to check this?

 

[eilerts]

Installation guide for TP-10 says (for the cable attached to the unit)
Brown +12V
Blue 0V
So there you know the current configuration on the plug.
Turn on the power to the socket and check actual configuration of the socket with the multimeter. Select DC V on the multimeter, check that the black cable of the multimeter is pluggen in at COM. If you see a positive number on the meter, then you are pointing at the +12V with the red pin, if you see a negative number, then +12V is at the black pin. Change your plug accordingly.

I hope this is useful and I did not misunderstand your question. Check you own manual in case things are different there

 

[steve yates]

Pefect, that lets me check the polarity on the socket and i can wire the plug to match. It will also confirm I am getting 12v at the socket and there are no problems there.
Thank you.

To check continuity on the black cable from the tp itself, what kind of resistance readings should the meter show? Does anyone who has done this know?

 

[jamie N]

From the pin on the plug to the 'inside' of the TP itself, virtually no resistance at all: "0.01Ω".

 

[andsarkit]

Short the two probes together and this will give you a reading for the probe cables and meter error. Hopefully this will be small and not much more than 0.1Ω but some cheap meters may be more. Subtract this from the reading from the TP cable to give an accurate measurement. I doubt a basic meter will read to 2 decimal places but if the cable resistance is only about 0.1Ω you should be OK.
If you want to investigate further you can find the service manual online but it seems like you only have a power cable connection problem.

 

[steve yates]

Looks like I have a problem on the supply side as well as that loose cable. The sockets reading flickers between 0.24 and 0.04v , snd when i checked resistance across the tow sockets ( with power off) it just reads I. Next step is remove the socket and investigate but as it was pissing down I’ll leave that for a dry day.

 

[andsarkit]

If I understand correctly you measured the resistance between the + and - on the socket with the power switched off. This should be infinite or open circuit and may be shown as 0L (for overload) on the meter. That doesn't tell you much.
You definitely want to see a solid 12V on the power socket when switched on.

 

[Alan S]

There is a possibility that it has been destroyed by reversing pos and neg. A lot of 12V electronics is susceptible to this.
Ask me how I know

 

[andsarkit]

There is a possibility that it has been destroyed by reversing pos and neg. A lot of 12V electronics is susceptible to this.
Ask me how I know ☹

You should be OK with that. From the service manual:

 

[jamie N]

Steve, if it was me I'd follow the Volts. Go to the switch where you turn on the power to it. Check the Volts there, it's quite likely that the pins are quite close together so it could be an idea to put your negative probe directly onto the battery negative, having a lead with croc-clips is perfect for this. Then go to the + on the switch, and follow the Volts through any connectors or fuses to the socket. If you've Volts at the socket, then you're into the lead and the unit itself, which would be your next step.
With any fault finding (as you know fine) don't make the fault worse, thus separating the probes, which also gives one an extra hand free..
Apologies for writing in this manner as I do know you to be an intelligent and skilled bloke, but I wanted it to be as clear as if someone was explaining to myself!

 

[eilerts]

Looks like I have a problem on the supply side as well as that loose cable. The sockets reading flickers between 0.24 and 0.04v , snd when i checked resistance across the tow sockets ( with power off) it just reads I. Next step is remove the socket and investigate but as it was pissing down I’ll leave that for a dry day.

Not uncommon in a boat that there are two or more problems working together to confuse you. Before you get into destructive modus, and since you describe yourself as a total novice with the meter, are you sure you did not accidentally set the meter to AC V. If the selector does not say DC or AC, look for V and a double line, one whole and one dotted. (Same apology as above)

 

[steve yates]

I tried both just to be sure tho was fairly sure the wavy lines were ac, as they only had 200 and 600 options.

 

[Alan S]

You should be OK with that. From the service manual:
View attachment 149131
View attachment 149132

Correct, but not in every case, at least not the VHF radio I bought in my local chandlery. Big spark then nothing! Realised right away what I'd done, took it back in all innocence and got it replaced free of charge.
Still pricks my conscience when I think about it.

 

[andsarkit]

Correct, but not in every case, at least not the VHF radio I bought in my local chandlery. Big spark then nothing! Realised right away what I'd done, took it back in all innocence and got it replaced free of charge.
Still pricks my conscience when I think about it.

Don't feel bad about it. Marine electronics should be designed for the the boating environment which includes untrained members of the public making incorrect connections. Skimping on the price of a protection diode which is pennies is not good practice.

 

[Blueboatman]

Old school suggestion
Wire a 12v incandescent type light bulb( so it draws a decent load , not some led thing ) to the autopilot plug and plug that in to the socket and see what you get
Hopefully a nice bright light

 

[Alex_Blackwood]

Old school suggestion
Wire a 12v incandescent type light bulb( so it draws a decent load , not some led thing ) to the autopilot plug and plug that in to the socket and see what you get
Hopefully a nice bright light

That won't tell him if the polarity is right or wrong!

 

[Blueboatman]

That won't tell him if the polarity is right or wrong!

Correct
Adding : just touching the meter positive lead to one or other socket connector will show a +sign or not on the meter if it’s half decent, even the cheapos do that ..
( he could try it on a 1.5v battery at home first to see that too )

 

[steve yates]

I identified the polarity with the meter as suggested by an earlier poster, so thats useful. Thats when I realised the voltage was way down on what it should read.

 

[Boathook]

Pefect, that lets me check the polarity on the socket and i can wire the plug to match. It will also confirm I am getting 12v at the socket and there are no problems there.
Thank you.

To check continuity on the black cable from the tp itself, what kind of resistance readings should the meter show? Does anyone who has done this know?

Are you able to open up the socket ? They may have used the same colour wires which may assist.

 

[steve yates]

I will next dry day. Went down today to do just that but forgot my screwdrivers.