Farish Class 31 Problem

[B757-236GT]

Afternoon
I did try to work out the best place to put it but i felt it could go in about three depending upon the fault. I have a DCC Ready BR Blue Class 31. It seems to have a fault in that while one way it runs fine, its completely dead the other way (no lights either). The motor works in both directions when you put power directly to it.

The odd thing is when turning over the blanking plug (i know as a 6 pin it wont be completely right) but it runs fine in the direction it previously didn't work in. I have tried blanking plugs so would i be correct in assuming the fault is in the PCB? The other trouble i have is that Farish only have the new next 18 PCBs in stock which are slightly different size and have a different type motor.

Does anyone have any ideas before i try a to find a PCB (new or good used) and have all the hassle of changing it over.
Thanks
Richard

[ntpntpntp]

Any sign of a short circuit - does it trip the controller in the non-working direction or is it open circuit?  Wondering if a diode on the main board has failed.  If alternative blanking plates give the same results then that does indicate the main board is the problem.

[jamespetts]

I am also wondering whether a diode on the circuit board may have failed. You can test the individual diodes with a multimeter if you have one.

One possible fix is to strip the circuit board entirely and hardwire the locomotive, although you do have to know where to solder everything (and where to put resistors, or else you will blow the LED lights) for that.

Alternatively, you could see if you can find a replacement PCB on Peter's Spares.

[Malc-c]

I recently needed a replacement PCB or my Farrish class 31 (BR Green) after a failed attempt to add a Hornby TT sound decoder.  I ordered one with the 6 pin DCC socket form Bachmann

https://bachmann-spares.co.uk/category/5-graham-farish-diesel-loco-spares/class-31/electronics

From my correspondence this will fit all 31's of this tooling, and for £20 you get new lighting boards too. - Their website is showing the item is in stock
 

[Farmer chap]

Hi,

I've just had exactly the same problem on one of my class 31's.

Definitely a failed diode so I replaced the PCB with a swapped out one from 'Delticnapier' on Ebay, Don't know if he has anymore available.

Working fine now.

Ian.

[ntpntpntp]

Replacing a failed diode shouldn't be difficult and will only cost a few pence,  if you know how to use a multimeter to identify it (either open circuit or shorted out) and a soldering iron to replace it. 

Over the decades I've had directional lighting diodes fail on various brands of model, more often shorted out and passing current both ways.

[PLD]

It is a regular and known fault with the Class 31 (but seemingly rarely with any other farish diesels). It is diode D2 or D3 on the PCB. If you're confident in your soldering skills to replace the diode on the PCB its <£1 fix. Otherwise, its a 5 minute job to swap the entire PCB. Farish will charge you £20+ for a PCB or they regularly appear on e-bay in the £12-£15 range.

Similar previous threads from with a lot of good advice:
https://www.ngaugeforum.co.uk/SMFN/index.php?topic=34910.0
https://www.ngaugeforum.co.uk/SMFN/index.php?topic=37502.0
https://www.ngaugeforum.co.uk/SMFN/index.php?topic=52993.0