Alastairpell
I have a rather geriatric loco that hasn't run for some time but is in very good condition and has a 'modern' can motor:

Rivarossi H0 - 1658 - Electric 4-current shunting locomotive Ee 3 / 3lV - SBB

The ancient Lenz decoder was definitely not going to wake up anymore so I replaced it with a new zen and removed the RC interference suppression network on the motor. I have removed this on most of my other old locos with great success.

The decoder programmed fine but as soon as I tried to drive it the decoder popped. Not a surprise as zens have no overload protection and are unsuitable for old locos, anyway, as I didn't have anything else handy I thought if I didn't wire up the incandescent lamps I might get away with it but not to be.

So I did what I should have done in the first place and bought a Zimo which I have used to great success on my other old stock, however, as with the zen it programs fine but trips out as soon as you try and move it, even just 1 of 128 steps. Unlike the zen it resets rather than pops but same again when you try and drive again. The zimo has a 2.5 amp peak! 
I have double checked but the right wires are connected to the right bits of the circuit board. 

I have waffled on a bit but my question is the RC network had wire wound resistors and, now that they are on the way to landfill, no longer able to be refitted, whether they performed some sort of current or surge limiting and I should have left them in series? As a check I lifted off the small circuit board that sits atop the motor and it doesn't trip out even if full power is applied. I insulated the bottom just in case and checked the motor connections were not shorting out anywhere but all okay. 
If it is not the lack of RC components then the motor must be short on the windings or I have done some other faux pas.

Anyone any ideas? 

Regards 
Alastair
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AHJAY
We have Zen in lots of older locos but we do as we recommend in all our instructions and test on DC before installation so have no issues.

That sort of current draw problem will soon destroy every brand of decoder, as while the Zimo may have a higher peak it will get hot enough to fry eggs and fail if you exceed an amp constantly. I know because we lots of tests with every brand.

The wire-wound things you mention - they will not be resistors - they will be inductors.

No matter how old, it should not draw that sort of current. Remove the inductors and any capacitor across the terminals and wire orange and grey straight to the motor terminals. If its still high current then, it means a new motor is needed.

Ahjay
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Alastairpell
Thanks Ahjay, never thought to wire directly to the motor as a trial, will have a do at that. I will have to wire up a siding with switchable dc/dcc as I don't currently have dc ability. Would your advise be to convert previous dcc locos back to dc to test them before replacing the decoders if they have not been run for some time or just newly to be converted locos?
Until now I have just assumed the ancient decoders were paggard and stuck a new one in, apart from my previous current limit oversight I have got away with it until now.
Cheers 
Alastair 
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AHJAY
New locos can often have faults and as for old ones, old oil goes solid over time and other things can fail while things are in a cupboard, so I'd test any loco I was going to install.

If you have a meter then set to amps and put it in series with one feed to the rails of your test track. You could perhaps use a PP9 battery as a DC source if you do not have a DC controller. If its drawing more than say 250mA then I'd service it fully and re-test before adding a decoder - nothing should really draw more than that as a "light engine".

I'd also replace all incandescent bulbs in older locos - a 12v bulb can get hot enough to melt the plastic loc body at DCC voltages.

Ahjay
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