Class 50 loco causing EO error code.

[Potrail2378]

Hi, I have just been gifted a Hornby class 50 (50 045) weathered loco, R number 2350. It works really well on DC, and all the light are illuminated.

As soon as I remove the blanking plate and put it on DCC track, (I have tried three different decoders) it shows 'EO' on my Hornby Select with a 1 amp PSU, and it shows 'Error' on the Hornby Elite with a 4 amp PSU.

All other loco's are fine. Can you please suggest anything to help me?

Thanks in advance.

Mod note - title amended to aid future search and better reflect the problem.

[P-Henny]

There are other recent posts regarding the Hornby Class 50 PCB. Early Class 50's had a factory faulty PCB where pin 7 and pin 3 of the 8 pin socket were crossed. This factory wiring fault doesn't affect normal DC running, but burns out ANY decoder you plug into it causing a short circuit (EO error code). Your three decoders you have tried are now probably only fit for the bin. This Class 50 PCB issue has been well known for some considerable time and documented on this as well as other forums. When this factory fault was first identified, Hornby offered free repairs or free replacement PCBs for those wanting to repair DIY. Can't say whether Hornby still do this after such a long period of time. Ask them.

[Potrail2378]

Hi, and thanks for the reply.

So if, as you say, pins 3 and 7 are 'crossed' I can simply cut the green and blue wires at the pins, swap them over, and re-solder them?

Thanks.

[96RAF]

Wire socket per this, ensuring there is no solder tracking between pins as this has also been seen:

[Potrail2378]

Hi 96RAF, yes I understand that, thank you. I'm just trying to establish what pins need swapping over to stop the EO code (and of course, to stop blowing my decoders)

[96RAF]

I am not sure swapping pins 3 and 7 will make any difference. It is no different to plugging the decoder in the wrong way round.

The only sure way is to check each and every socket pin goes to the correct output connector on the PCB, which will prove the traces on the board are not crossed.

I would also be searching for those other posts as I remember a member had traced various boards and drawn up their schematics.

This looks like one of them but note although the socket colours are correct the socket pin numbering is wrong.

[ColinB]

Does it really kill the decoder or just kill the function output on Pin 3? Having said that an E0 display means a short, so probably the decoder is dead. I know this is an error from a long time ago, but it is a fundamental mistake. I assume when they designed the PCB they got confused with the underside and top on the connector PCB when they laid it out (our hardware guys were always doing this). So I assume the fix is to cut the tracks to these two pins and hard wire them. I assume the front and rear lights are the wrong way round as well.

[P-Henny]

Does it really kill the decoder or just kill the function output on Pin 3?

 

 

The Class 50 PCB fault results with a negative earth derived from the PCB circuit being connected directly to the Blue decoder wire positive output, thus it is the positive output of the decoder that is short circuit and not the function output. This burns out the power supply circuit to the decoder itself rather than a function.

[P-Henny]

I assume the front and rear lights are the wrong way round as well.

 

 

No, they are unaffected as they do not use pin 3 nor pin 7. The Class 50 PCB generates its own lighting positive supply to support DC working, so the decoder pin 7 positive output is technically unnecessary. On a correctly wired Class 50 PCB, the pin 7 positive is in parallel with the PCB generated positive. A correctly wired Class 50 PCB is a clever design as directional lighting control is auto switched via semi-conductor components to use either DC rail polarity OR decoder FO control to operate them.

[Potrail2378]

"Early Class 50's had a factory faulty PCB where pin 7 and pin 3 of the 8 pin socket were crossed"

So, just to let me get this straight - Pin 7 and Pin 3 are 'crossed', as in they need swapping over? Or is there a dead short ('crossed') on the circuit board?

Either way, with a little info, it should be an easy fix.

Thanks in advance.

[P-Henny]

@Potrail2378

A previous Class 50 PCB thread located somewhere on this forum described an easy fix. From memory, the fix was to cut the tracks on the PCB that connect to pin 7 and optionally (recommended) to pin 3 of the 8 pin socket mounted on the PCB. With these tracks cut, the PCB uses its internally generated positive supply to power directional lighting. Cutting the track to pin 3 just disables the decoder green function wire which is rarely used anyway. The cut tracks then prevent the DCC decoder from being short-circuited by the PCB fault. This simple fix did not require any additional wiring to be added to compensate for the disconnected socket pins.

[ColinB]

P Henry I can understand your description, the negative earth shouldn't be going anywhere near a pin other than via the base of a transistor/fet which in the mis wired case is a function output. I can see how it can happen you blow the open collector output which creates a short to the negative rail, normally it would just blow that function (been there done it on a TTS). Has anyone had issues with lets say Zimo decoders failing. The dear old Hornby decoders have virtually no function output protection whereas other makes do.

[james_nelmes]

Potrail

start with the basics - check to see if there are any shorts in-the loco. Use a multimeter in resistance mode or even better continuity. There should be no connection between each side of the loco (wheels) and the motor. Check the 8 pin connector to ensure there are no shorts between the pins. You can undo the plug and check the underside for shorts. In a single post I cannot describe all tests but it sounds like a short of some kind.

[james_nelmes]

Potrail

start with the basics - check to see if there are any shorts in-the loco. Use a multimeter in resistance mode or even better continuity. There should be no connection between each side of the loco (wheels) and the motor with the blanking plug removed. Check the 8 pin connector to ensure there are no shorts between the pins. You can undo the plug and check the underside for shorts. In a single post I cannot describe all tests but it sounds like a short of some kind.