Fault-finding Hornby Dublo 2-8-0 48073

On 22/04/2007 18:34, gb said,

You wouldn't happen to have an old three-rail version, would you? If you have, the tender should have plunger pickups on it to pick up from the centre rail (or studs?)

Well, no. What is a plunger pickup ? The tender doesn't look as if it is missing any fitting. It does have two empty cast holes just inside the front and back wheel shafts. Doesn't look as if they held anything though Giles

Could be a signal interference supression capacitor ?

Suggests one set of wheels is insulated (the left) but if so then there should be something to pickup current from the wheels to that thin insulated red wire on the left. If the current collector is on the wrong side of the insulation (even partially) then you will get a short. Insulation can be a very thin band inside the tyre or at the axle.

Lots of locos pick up current through non-insulated wheels on one side.

Cheers, Simon

>

Does sound as though it's one of the old third-rail models. The two-rail one was numbered 48773 if I remember correctly, representing an example which was returned by the War Department in 1957/8, about coincident with the introduction of H-D two-rail electrification. Brian

On 22/04/2007 18:47, gb said,

If it was three-rail, those two empty cast holes would have had a spring-loaded brass plunger in each, which would provide one of the electrical polarities. That's all hypothetical though, because you don't have the three-rail version!

The wheels on the right hand side (looking towards the front from the cab) should have an insulating bush in the centre to insulate them from the axle. The front and rear right-hand wheels have the wire pickups rubbing on them that I think you are describing. If you are saying there are no "rubber grommets" on any wheels, then you have a problem - these should be pretty obvious (mine has been converted to Romford wheels, and I can't remember exactly what the originals looked like). The right-hand wheels and the motor connector that the red wire connects to should be insulated from everything else - and yes, they did shrink-wrap components in the 60s, although it has probably fallen apart with age by now. The part you're describing is the interference suppression circuit.

When you say that the two sides short out, what exactly do you mean? Is the resistance across the two sides zero ohms as measured on a multimeter, or is it that you are sticking it on a track and the controller is tripping out? If it's the latter, it might well be simply because the motors in these things draw a hefty current, and with stiff wheels it might just be too much for a modern controller.

Sounds more like an inductor. Both are used for interference supression.

(kim)

If it is then that's the problem - it should be in series instead of shorting out the motor.

The two tender holes are all painted up so not a three rail system (unless the tender is alien). The multimeter shows zero ohms across the wheels. And the 2 amp (15v dc offload) supply also trips out.

However the comment made about the pickup connectors rang an alarm bell. The insulating cover is cracked. So I pulled the red wire clear of everything and "Eureka". Across the wheels: Now open circuit Across the motor: 3 ohms Across red wire to other wheels: 7 ohms Conclusion - a short created by the pickup wires somehow - as suggested.

When voltage applied with the wheels upside down and the trip jammed shut (tut, tut): Voila the wheels went round without hesitation and reasonably enthusiastically, forward and reverse. Current drawn was a somewhat startling 3.8 amps !!!!! Can't be normal surely ?

Presumably WD40, Silicon spray or 3-in-1 oil would help this functioning wee beastie and bring current consumption down.

Many thanks for all your musings which eliminated cul-de-sacs and pointed to the culprit. In retrospect - obvious but it always is once you know the answer

-- Giles

Glad to hear you've found the problem, Giles. 3.8A does sound a bit on the high side- is there any overheating of the motor? Be careful with lubrication, eschewing the more aggresive products like 3-in-1 and WD40- some attack the plasticisers in components such as insulating bushes, causing them to fail- I speak from bitter experience. Brian

Well, the owner lent me a little power supply, a Smoothflow Minimodels Ltd 12v dc 2 amp power supply. It has a lovely selenium bridge rectifier which will take 3.8 amps for a bit without wincing (unlike modern diodes). But I am loathe to hammer it above the 2 amp nominal limit. So I do not know whether the motor overheats. It must do. And I suspect the thin red wire is too thin to take that sort of current.

It gets worse. That 3.8 amps was with the motor just driving wheels in the air, no-load. The engine has a large lump of yellow-painted lead abover the wheels, presumably to improve traction. Which would suggest it is actually supposed to pull a loaded string of carriages up an incline like the "heavy freight engine" it symbolizes. The mind boggles at what current that will draw !

There is no answer to "migration of the plasticisers" with time and I would not wish to accelerate that process. When the motor is out, the wheels rotate freely. The motor is a bit stiff. But it is the slanting worm gear which seems to introduce friction.

If lubrication would help what would you suggest the owner tries - silicon grease only on the worm gear ? I was wondering whether clock oil is better but clockmakers hate putting oil on cogs because of the dusty sticky mess that ensues.

Still 3.8 amps offload is too much.

-- Giles

You could try taking the motor out and seeing how free running the wheels are and lubricate the bearings with one of the Peco products such as Electro lube. In normal operation my Wrenn unrebuilt BoB draws about

2A on a stall test.

Had some fun converting that model to DCC.

Chris

"gb" wrote

It's not normal - it's a sure sign that the motor needs remagnetising [1]. If you continue to use it without doing so will result in the motor burning out and as spares are long since finished you'll then be looking at a specialist to rewind the armature.

[1] permanent magnets were few & far between in the late 1950s when this model was released.

John.

After youve done that then clock oil is recommended for cogs by Iain Rice so must be the best. Also a tiny drop at the motor bearings. The peco electrolube is commonest for rest of chassis.

Also when you get it back you might want to run it in properly before re-installing. With motor not on chassis. Can give details as per Iain Rice if you like. Cheers, Simon

Why not get proper replacement magnets?

A friend of mine bought some & he said it transformed the performance no end.

Thank you for all the pointers on how to keep this behemoth running without plunging the nation into darkness.

I looked at the website you suggested and it says about the magnets: ..."They are a direct replacement, simple to fit, are charged for life and "No more Re Mag's".

The words "simple to fit" are, in my experience, one of the world's great lies (together with: I love you, the cheque is in the post, some of my best friends are ...politicians, I am so very sorry, etc).

Still when the lambing, harrowing, shearing and hay-making are over and autumn is here again, I think we will try a replacement magnet, some clock-oil and electrolube. Because the alternative seems to be to put the locomotive on the shelf. Which doesn't seem right somehow. Amazing how addictive these models become.

Many thanks

-- Giles

What about put the sheep on the shelf, build a layout and play trains ?

Cheers, Simon