No signs of life in 2nd hand servo

[colmo]

I bought a KO Propo 2113 FET servo from another Oople member, and just got around to fitting it in a car.

Alas, the servo showed no signs of life when I powered up the car or tried the steering wheel.

I was careful not to plug it in with reverse polarity.

What is the most likely explanation (apart from 'It's dead, Jim')? Is there anything I could do to test it?

[losixxx]

have you wired up the fet lead to the ESC?

[colmo]

Aha, that's what that spare wire was...no, I haven't - where does it attach? (sorry, noob alert)

[Mike Hudson]

it connects to the positive terminal on your esc or the fet wire wire on the esc if it has one with a fet choke connected inbetween

[Southwell]

You must get a fet choke for it or you risk getting interference.

[colmo]

Originally Posted by Mike Hudson

it connects to the positive terminal on your esc or the fet wire wire on the esc if it has one with a fet choke connected inbetween

Either way, is the FET choke necessary?

Edit:

Originally Posted by Southwell

You must get a fet choke for it or you risk getting interference.

I guess that answers it.

Thanks all, I now have to get my hands on a FET choke in quick time...

I've been told the choke also protects the servo from being fried by voltage spikes.

[jasonnjane]

so the big question...are you sorted now

[colmo]

Cheers for the concern (always good to deal with a conscientious seller ) - I just need to acquire a £1 FET choke and I'll be grand - don't want to risk it without the choke.

[Southwell]

+ heatshrink

[colmo]

Originally Posted by Southwell

+ heatshrink

Got some (4mm, is that wide enough?)

[colmo]

There are no model shops close to hand with a FET choke in stock. However, Maplins do have chokes. The likely candidate is the 10uH part, sku WH35Q - as indicated on this RCTech thread.

If this is the one, I'll buy a handful to keep me going a while - can anyone confirm the 10uH choke is the right one?

[Mike Hudson]

No idea what the actual value of the choke is but it sounds about right

[colmo]

Thanks for the offer - there's no need, I'm in the big city (well ok, Belfast..big-ish) for the weekend and there's a Maplin within walking distance - I could just buy a handful of them all against the time we do actually find a correct value.

To muddy the waters, I found NRGDynamics chokes stating specs of 3.3uH, 900mA max current and 0.29ohms resistance. That matches most closely with the Maplin part of 4.7uH, 820mA and 0.34ohms resistance. I note the 10uH unit can only cope with 680mA, while the 2.2uH unit can handle a full Amp.

[colmo]

I finally found a prior reference right here on Oople.

Due to the vague reference to 4.7, I'll get the 4.7uH part...or several, actually. At 44p, not a bank breaker, even in these hard times...

[Southwell]

I have a couple at home, i will check them later.

[colmo]

Originally Posted by colmo

Due to the vague reference to 4.7, I'll get the 4.7uH part...or several, actually. At 44p, not a bank breaker, even in these hard times...

I tested out the servo yesterday, fitted with the 4.7uH choke, and it worked like a charm. Steering is extremely responsive. I couldn't be happier with it