Class 56 R2781SX not moving

[NorthPolePete]

Hi - I have a R2781SX Class 56 DCC which hasn't been used for 5 years or so. I fired it up today on the DCC track and the sound and lights work OK - however it didn't move. A friend investigated and stripped it down and confirmed the motor spindle and worm drives both rotate and turn the wheels when operated manually. The yellow component on the 21 pin DCC decoder becomes extremely hot when the unit is attempted to be run and the sound indicates it should be moving - and we have had it creep along extremely slowly for about an inch. We have tried both DCC and DC to noavail. From stripping down the moving components we don't believe anything is seized up - so we are thinking that maybe an electrical problem is causing the decoder to overheat. Would anyone have an ideas on a way forward with this? Is the decoder likely to be faulty and and if so, would just getting a replacement do the trick, or do these symptoms point elsewhere at a fault we haven't discovered? Any assistance gratefully received. 

[96RAF]

You will be lucky to locate a replacement sound decoder as they were either ESU v3.5 or maybe v4.0. The speaker ohm-age will tell you. 100 ohm for the v3.5, 4-8 ohm for the v4.0.

The decoder is likely overloading and getting hot either because the motor is worn out and drawing more current than usual or the mechanism is stiff and causing the motor again to draw too much current. Clean and lube the bogie gear towers, check the motor stall current (on DC with a blank fitted in lieu of the decoder). Go ahead from there.

[Fishmanoz]

Hi NP Pete, welcome to the forums.  I’m coming from much the same direction as Rob with my advice - motor or decoder problem.  I’m going to assume the stiff mechanism has already been eliminated by the maintenance you’ve done but it’s worth double checking as per Rob’s. 

 

More likely at this stage is electrical problem with the motor and a stall current test is the way to go.  This must be done on DC with a blanking plate replacing the decoder.  Then you need to put an ammeter capable of handling 2 Amps or more in series with the DC supply and load up the loco progressively until the wheels are stopped briefly (against buffers or press down on it, again only briefly) and check how much current it draws.  On light load it should be under 250mA, at stall under 500mA.  If over that, it’s an indication the motor is worn with the magnets weak and a replacement motor indicated.  

 

If stall current looks ok, then I would be thinking decoder and looking to install another one to check.  No need to go for ESU to test, just something basic without sound will do.  You need to either use a 21-pin decoder or a 21-8-pin conversion harness and something like an R8249.

 

 

If you don’t feel up to that, then maybe a visit to your local model shop, if such a thing still exists in your area.

 

 Let us know how you get on.

[richard_croft]

I’ve repaired several of these with these symptoms and it’s always been the motor which has been seized, I’ve managed to repair them with no new parts. My advice would be to stop trying to run it with the decoder in because you are likely to burn it out. Take the motor out of the model, turn it by hand a few times. Also take the top off the bogies and make sure they aren’t dry. Put it back together, fit the blanking plug and just run it as much as possible, it might even make loud squealing noise for a bit but eventually this will stop, then you can put your sound decoder back in. It’s always worked on the ones I’ve done for customers.

Richard

[NorthPolePete]

Thanks all for the advice here. I've so far put a DC blanking plate in the diesel but no luck getting it to move there. So will progress through the other things to try over the next week. Cheers!

[ff2nd]

With the Hornby twin drive locos, especially if they have been left for a while, the usual culprit is the grease on the worm shaft "hardening", meaning that it won't turn. Flip one of the bogie covers off the top of the shaft, then have a look at the worm itself. If you see anything that looks green, it needs a complete clean and service. If you remove the drive shaft, and holding the end square bearing, can't spin the shaft at all, then they are congealed at both ends of the loco.