servo wires

Just bought new spektrum Dx7 and receivers and hoping to put into my high wing asap. My question is, the orientation of power and signal cables is different on the new recievers to my old 35mhz, and the wires to my servos are two black and a red (sanwa servo's). Im sure they will need swapping around somehow to suit the new receiver anyway, but is there any way of telling which black wire is negative and which is the signal wire without destroying the servo or new receiver?
Also some of my new micro servo's have red/white/black wire layout which doesnt seem to tally to the orientation of the spectrum receiver (im assuming the white wire is the signal) - is it commonplace to have to swap wires around to suit rx's nowadays? I dont ever seem to remember having this problem back in the day!

That's a realy good question! As far as I know, servos normally have the positive wire in the middle, and the signal/negative wire on the outside. To determine which is which, you should be able to connect it up. So long as the positive is in the right place (i.e. the middle), you shouldn't damage anything if the plug is upside down.

The other way to do it, is to connect the sanwa receiver up with power, but no servos in. Switch your tx on, and get a multimeter, or oscilloscope on the output. You should be able to identify which pin the positve connection is on (put one probe on the battery negative lead, and use the other to test the rx pins). The positive pin will have the battery voltage on it. The negative pin will have zero volts on it, and the signal pin will have a voltage somewhere between the two, probably nearer zero though.

I'll pop a meter in the van for tomorrow evening though, we can test that at the field if you are not sure about doing it yourself

Andy

If I remember Sanwa servo leads are wired differently I think the pos & neg are reversed.

These threads may help

http://www.rcgroups.com/forums/showthread.php?t=1267679
http://www.rcuniverse.com/forum/m_533579/anchors_533581/mpage_1/key_/anchor/tm.htm#533581

If you plug Sanwa stuff straight in you'll let the magic smoke out

True
The smoke comes out of the servos, it's white and smells orrible.
They don't work afterwards.

Old Sanwa servos had a 3 lead ribbon cable made up of two black and one red lead. The plug was the same width as other makes but much thicker wih 3 moulded ribs to ensure the plug only fitted one way round in the socket.
Hitec also made Sanwa compatible servos too with the same plugs and cable.
These are all wired differently than all other makes. .
The wiring on these is:-
Red outer positive 4.8v
Centre Black Negative
Other side Black Signal

If you take the bottom off, 4 screws, you can see the red and negative go to 2 different large wiring lands each with many components. The signal wire goes to a singe connection.

They were good servos and work fine with modern plugs except they had carbon pots and didn't do well when old or exposed to a lot of vibration.

The nice thing about the modern stuff is that if you connect plugs the wrong way round no damage is done, they just don't work until you correct it.

And of course
The modern way is Red centre pin- positive
black/brown and signal white(JR) or ?? futaba either side.
Check one to see which handing is correct for the plug body . Two types JR and Futaba, very similar

JR /Spektrum are actually
Negative supply Brown
Positive supply Red
Signal Orange.

Picture shows each plug from underside(pins visible) and top(pins hidden)

Old Sanwa
The underside also has 3 ribs to prevent incorrect assembly
Red (outer) Positive supply (actually connects to motor positive)
Blk (centre) Negative supply
Blk (outer) Signal

JR & Spectrum
Brown (outer) Negative
Red (centre) Positive
Orange (outer) Signal

Futaba
Blk (outer) Negative
Red (centre) Positive
White (outer) signal

JR & Spectrum are interchangeable
Both will fit Futaba if plug body is modified