Atco mower electrical problem

[w1bbles]

Here’s a long shot…

I have an Atco GT30 H ride-on mower. The starter motor is turning over very slowly but if I short the solenoid it starts no problem. I’ve tested the switching (ignition) voltage on the control terminals on the solenoid and I am getting only about 6 volts between the +ve and a direct to battery -ve.

The problem is that I can’t find a wiring diagram. The solenoid has 4 terminals: the ‘in’ and ‘out’ for the starter motor +ve feed and then the two control wires, which are purple and black. The c. 6 volt measurement when I try to start it is between purple and black control wires or between purple and battery -ve (I’ve tested both). I should have tested continuity between black and the battery -ve but it’s out in the shed and I’m too lazy to go back until the morning.

I have ruled out flat battery, poor starter motor connections etc as shorting the terminals with a spanner starts the engine. Resting battery voltage is 12.35 volts.

That means it’s likely to be (1) a fault in the ignition (key) switch or (2) a dodgy mower ECU. The ECU does appear to have one burnt pin but it’s on the main safety circuit and I’ve cleaned it and tested continuity. A replacement ECU is about £100 so it’s not a crazy idea to change it anyway due to the burnt pin.

My next step when it’s light is to check the condition of the ignition switch and also confirm that the black control wire on the solenoid is a permanent -ve.

If you haven’t nodded off after my blurb, does that sound sensible? Anyone experienced similar on an Atco or Mountfield?

[Richard-D]

You've nearly narrowed the problem down far enough but I wouldn't be changing parts yet. The next step for me would be to test voltage at various points in the starter circuit whilst cranking. You can ignore the negative side of the circuit as you know that is fine (as it starts when you short the starter terminals).

[finlo]

I would suspect grotty solenoid contacts as they either close or don't and bypassing them works.

[w1bbles]

Richard-D said:

You've nearly narrowed the problem down far enough but I wouldn't be changing parts yet. The next step for me would be to test voltage at various points in the starter circuit whilst cranking. You can ignore the negative side of the circuit as you know that is fine (as it starts when you short the starter terminals).

I agree - but the wiring is pretty inaccessible as it is ultimately a cheap semi-disposable machine!

[w1bbles]

finlo said:

I would suspect grotty solenoid contacts as they either close or don't and bypassing them works.

I didn't mention that I've already changed the solenoid as it was going to add yet more info to a rambling post. It's the 6 volts at the control terminals that makes me think that the fault lies elsewhere.

I've bought a new ignition switch as one of the terminals is quite badly corroded and I find testing resistance under load quite tricky. For £17 I thought it was worth the gamble. It arrives Monday...

[w1bbles]

I know this is a very niche topic but I've bodged the problem. After replacing the ignition barrel (no change) and the solenoid again (no change) I managed to melt the solenoid as the coil was bouncing in and out of contact, presumably causing internal arcing. All the wiring looked good, with no poor joins and all pins clean barring the ECU connector.

I therefore reckon that the ECU is faulty but I couldn't be bothered chasing down the problem and instead fitted a manual 12v 50A push button contact. I now have a mildly PH 'Engine Start' button and the Atco seems to be at peace with itself.