King Class loco not working with DCC

[Brew Man]

Wasn't sure whether to post this here or in General. Anyway, I bought this loco last week with one of Hatton's DCC Decoders. Fitted the decoder and... it didn't work. Well, it grunted a couple of times then nothing, except an EO error on my select every time it was on the track. After quite lengthy chats with Hatton's support I wasn't getting anywhere. Tried all their suggestions to no avail. Then I reverted it to DC operation and tested it on a short length of track with a DC controller, and..... it worked, albeit on a very short piece of track and quite buzzy. I concluded from this that the decoder was either incompatible or damaged. I read after I purchased it that their decoders aren't always happy with Hornby controllers, (it didn't mention that on the loco's description page). So, I bought a Hornby 8 pin which arrived yesteday. Excitedly I fitted the new decoder and got a few grunts and sometimes motion for an inch or two, then nowt.

Every other loco, 4 of them work fine. I've tried everything I can think of, including changing the decoder as mentioned but have so far drawn a blank. Aside of a fault with loco itself, does anyone think it could be the Select not sourcing enough power? I'm using the standard 1A PSU but have ordered a 4A one as I figured I'd eventually need one anyway.

Any help would be much appreciated. I'm waiting for an email from Hatton's

[ColinB]

From what you mention it sounds like that there is a fault with the 8 pin DCC socket wiring. I hate to say it but you may well be blowing up the decoders as you are fitting them. I am assuming it is a modern loco which should consume less than 500 milliamps. If by chance it is a second hand loco bought off Hattons and it is an old loco converted for DCC, then possibly the decoders cannot source enough current and are current limiting. I will assume it is a modern type loco, in which case you need to take the header out of the DCC socket and check continuity between pins with a multimeter. You should only get a reading between pins 1 and 5, the rest should be either give a high resistance vale of open circuit. If pins 1 or 5 are connected to track (pins 4 and 8) with the header removed, then that is your issue.

If by chance it is a converted old loco, then buy a Zimo or Train O Matic decoder, they have a higher current limit.

[Brew Man]

Thanks for the reply, Colin. The loco is new from Hattons. I bought one of only five left on the shelf and they have now sold out with no prospect of getting any more. I will try what you suggest. Do you mean readings between pins of the header, not between connections oo the socket?

If it is a fault with socket, (or anything else for that matter) it will be going back to Hattons for repair/replacement/refund.

[Chrissaf]

Do you mean readings between pins of the header, not between connections on the socket?

 

No he does mean between the holes on the socket once the decoder or DC Blanking plate (DC Pass through plug) has been removed.

 

Just to provide a bit more detail, it is not unknown for these sockets to leave the Hornby factory with a blob of solder bridging either Sockets 1 & 8 or Sockets 4 & 5 on the underside of the socket. It is this short on those connections that you need to look for with a Multimeter set to measure resistance. With the exception of Socket 1 & 5 which should be [if wired correctly] the electric motor, there should not be any connections between the other sockets.

 

Now this soldering fault does not affect DC running at all, because these socket connections are connected together by the DC Blanking plate when fitted for DC working. But once you replace the DC Blanking plate with a DCC decoder, the short applies DCC track voltage to the decoder output H bridge motor control circuit on the decoder and instantly blows it.

 

EDIT: Hattons provide a decoder fitting service on all the new DCC Ready locos they sell. If you had taken that offer, they would have found the fault and fixed it at their cost before shipping the loco to you as they test all their decoder installations as working before shipment.

[ColinB]

Yes, my post is not that clear, I wasn't sure what sort you had. Pull out the header from the 8 pin DCC socket that is screwed to the loco. Now measure the resistance between pins on the socket. I suspect either pin 1 or pin 5 will be connected to pin 4 or 8 or to the track. It is either that they wired up the socket wrong or there is a very fine solder link between the pins. If you do find a connection between the pins, unscrew the DCC scocket, turn it over and scrape down the gaps between pads on the socket with a thin bladed screwdriver. Unless it is an obvious blob of misplaced solder, then it is probably a hairline piece than you cannot see, scraping should remove it. I bought the blue BR King and I remember I had issues with the socket. I suspect yours is a later model, but Hornby do have history of miswiring this socket. Not that it helps you but I have noticed on their later locos, that they are using better sockets.

[Brew Man]

Well I've measured resistance on the socket and am getting O/C between all pins wrt all others. I am getting readings between some of the pins on the plug.

EDIT: hold on, I need to do this again as the socket is located on the tender and I had the plug between tender and loco disconnected. But that said, there isn't a short between any of the socket pins.

[96RAF]

A physical inspection of the underside of the socket is recommended using a magnifier. Remove the screws holding the socket in place and turn it over. I often drag an old dental scraper between the tracks to be doubly sure there is no cross feed.

 

There was one loco with a powered front bogie that was cross wired from the factory. Doesn’t help when Hornby wires its locos all in black, when coloured wire is the same price and would make fault finding a bit easier.

[ColinB]

You have definitely done in the downways and across ways directions. You should only get a reading between pins one and 5. The only other thing to check which happened with mine, is the DCC decoder header pins are ever so slightly thinner than the the DC header pins, with mine the DCC decoder header wasn't connecting properly with the the socket. Make sure it is pressed fully home. Don't do it while it is connected to the DCC. If not that, then I am sorry but it is a return to Hattons.

[Brew Man]

I shall try all that. Thanks, chaps.

[ColinB]

I think the colour of the wire is very variable, sometimes they use red and black, sometimes just black, on some it is grey. From their point of view if they use one colour then it is cheaper (better price per reel) and less wastage. The last loco I bought I noticed they were using much better sockets where it is less likely that you will get solder splashes across tracks.Trouble is, all the replacements sold by "Peters Spares" etc. are the old type.

[Brew Man]

You have definitely done in the downways and across ways directions. You should only get a reading between pins one and 5. The only other thing to check which happened with mine, is the DCC decoder header pins are ever so slightly thinner than the the DC header pins, with mine the DCC decoder header wasn't connecting properly with the the socket. Make sure it is pressed fully home. Don't do it while it is connected to the DCC. If not that, then I am sorry but it is a return to Hattons.

You might have hit the nail on the head, Colin. I have just plugged the header into the socket and saw that it is very loose, so the pins are indeed slightly thinner than the holes. I will try splaying the pins out very slightly to see if I can get it to fit snuggly. Will report back.

[Brew Man]

Nope, still no joy. I got the plug to fit snuggly in the socket and continuity measured OK, but still grunting and occasional move for an inch or two, then nothing. I'm not fiddling with it any more, it's going back.

Thanks for all the useful suggestions guys.

[ColinB]

The only time that has happened to me was when I fitted a gaugemaster decoder into a GWR pannier tank with the old scalextric motor. Basically those motors can take up to 0.8 amps which the gaugemaster decoder cannot source. In your case there is no such issue. It could be that the socket has an individual socket that is broken internally so when you push the header in it feels tight because the other 7 pins are. As I said with mine I replaced the socket and got Hornby to replace the one I used, but in your case a return is your best bet. Perhaps there is something wrong with the motor and it is drawing excess current. You would never notice on DC unless you measured it.

[Brew Man]

Just to round off this thread from before the forum went down, I ended up returning the loco to Hattons and got a full refund. Very shortly after I found the same model, (King Edward V) on another site which was new and even cheaper than the Hattons one. This time I got them to fit the decoder and, up to now it works flawlessly. Trouble is, I still have the decoder from the Hattons loco but am dubious as to whether to try it in another loco in case it has a fault and causes damage.

[96RAF]

Invest in a decoder test rig, such as ESU or the blatant LiaisDCC knock off.

You can prove a decoder on the rig, set its address and any other CV alterations you want to make and be sure that if it plays up in a loco then the fault lies in the loco.

[Brew Man]

Good idea. I'll have to check how much they go for to consider if it is worth the expense.