Installing 8 wire decoder to 4 wire Loco

[Deem]

I hope everyone is OK and in good health,

Need help,

I have Hornby Class 08 DCC fitted - have Hornby R7274 in Loco and I don't like the way Loco run in DCC mode. Need much more throttle before Loco will run at decent speed.

I have checked pickups, installed new wheel set but Loco still struggle in DCC mode.

I would be grateful if someone can advice, can I install 8 Wire decoder instead of 4 wire which is factory fitted.

If yes which wire I would use and where would I connect.

Regards

[Fishmanoz]

Hi Deem, I suspect you will get nowhere by making such a change, particularly if all you do is wire in an R8249. The reason is that the two decoders are the same design, just the function wiring is different. I would expect no difference in motor control between them.

Are you sure that what you are seeing from your 08 is not just because it is a shunter with very low top speed and the need for fine throttle control, despite the differences you see in DC mode versus DCC?

[96RAF]

@deem

R7274 is a 4-pin decoder and likely wouldn't plug into a 6-pin socket. If your decoder is 6-pin Hornby it will be an R7150.

[ColinB]

As Fishmanoz says, there is no difference between a 6 pin DCC decoder and an 8 pin except for the wiring to the connector. Some of the 6 pin ones I have seen for N gauge are a bit limited on power, but I doubt this is the case with your one. I have found there is subtle differences between the way decoders work, but Hornby is one of the better ones. I use Zimo ones as I found that they seem to be the best at running, so if you are that concerned replace your existing one with a new 6 pin Zimo one. Of course the existing decoder may have a fault, which may explain it, so replacing it may prove the point. If you do find the decoder is at fault don't bin it, use it for test or cases say in a DMU or EMU where you need a decoder to control the lights in the dummy end. Whatever you do label it, so you don't go through the loop again. I suppose the only other thing is that the motor in your loco is pulling more current, so the decoder is struggling to provide it. In DC mode you wouldn't notice. My Bachmann shunter is incredibly slow, but it is designed that way.

[Deem]

Thanks to all for their input,

I was considering Liasdcc 8 pin decoder (for this decoder I would need advice).

My reason for using the Liasdcc 8 pin is

I had Cock O the North with Hornby R8249 which was using lot more throttle power compare, to my second Cock O the North in which I install the Liasdcc decoder.

So I replaced the Hornby R8249 to Liasdcc 8 pin decoder in Cock O the North which worked much better compare to Hornby Decoder.

So question remain

If I was to use 8 pin decoder, which wires I will be using in my class 08 with 4 pin decoder and even it is possible at all?

96RAF - you are right, correct decoder with 6 pin is R7150. But I removed the body to make sure which decoder I have, so it is R7274 with 4 pins. My mistake is I thought it was 6 pin but actually it is 4 pin decoder.

Regards to all

[Fishmanoz]

First question - are you sure it doesn’t have the 4-pin socket fitted? Those sockets aren’t mounted flat on the chassis but on their side in front of the motor.

For pin assignments, google Brian Lambert, go to his DCC pages and he has all the socket wiring info there.

But it’s pretty simple for an 08, only 4 wires involved - disconnect the wires from the pickups attached to the motor and discard the capacitor. Now solder decoder red and black to the pickup wires, one each side, and decoder orange and grey to the motor connections. Trim all other decoder wires and cover the bare ends of them to avoid any shorting.

If the loco runs backwards to what you were expecting, swap orange and grey (red and black can go either way). So test first on ID 03 before you refit the body then reprogram to your preferred ID.

[Deem]

[Deem]

Thanks Fishmanoz

I am waiting for the new decoders to arrive and I will try to follow your advice.

Regards

[Fishmanoz]

Call me Fishy please Deem, everyone else does.

In your first photo, that’s your 4-pin socket on the right, can’t tell what is plugged into it. Or it’s on the left in your last 2 photos. Not a decoder? If not, it must be a blanking plug for DC.

Simplest DCC fit - just buy the Hornby 4-pin.

[96RAF]

In the first photo it looks like a four pin decoder fitted into the slot provided on the left hand side as seen with the plug engaged with the four pin header on the right hand side.

All the gubbins under the kapton tape is likely to be wiring to the motor, chokes and capacitors.

You could unplug the decoder slip it out of its slot and post a picture of both sides of that for comparison with R7274 catalogue picture.

[Deem]

[Deem]

96RAF

I bought this Decoder from Amazon and it is R7274 - 4 pin decoder. I had to check with my son who have confirm that when he ordered this decoder, it was R7274.

Regards

[Fishmanoz]

Given all of this, if I were fitting another decoder, I’d be looking to fit a 4-pin connector on whatever decoder I was going to fit, or even individual pins onto decoder red, black, orange and grey, to plug into the existing socket. You can use the existing decoder to tell you which color wire goes to which socket location.

From Sydney, I have no idea what hardware you need to buy for that, but I’m sure someone over there will know?

[96RAF]

@deem

I bought this Decoder from Amazon and it is R7274 - 4 pin decoder. I had to check with my son who have confirm that when he ordered this decoder, it was R7274.

R7274 is indeed a four pin decoder and correct for the model but in your OP you inferred it was a six pin decoder and the following replies perpetuated that error, hence why I listed all three variants of what is essentially the same decoder. You can make any one into any other one by soldering on the appropriate wires and plug.

[Fishmanoz]

Rob, the problem is Deem doesn’t like the way this decoder runs the loco and it clearly doesn’t matter what pin version of it you use, the running will be the same.

The correct question I believe is - what 4-pin plug do I buy to get another decoder make fit the 4-pin socket on the loco? Assuming of course he doesn’t want to cut both plug and socket off and hardwire. Perfectly acceptable from a functionality point of view but still not ideal.

[ColinB]

That is exactly why I replaced all my 4 pin connectors with 6 pin ones. So sorry to be blunt but you have two choices stick to the Hornby 4 pin or rewire the loco to 6 pin. Wiring to 6 pin means you have a much larger choice of decoders, even sound ones, as far as I know nobody makes a 4 pin sound decoder. I personally think that the current limit for a Hornby decoder is marginal for the motor that they fit into their 0-6-0 locos, some of those motors draw more than the 500 mAmp limit. If you can't rewire it then accept that you will only be able to use Hornby 4 pin decoders. I only use Hornby decoders on brand new, modern locos.

[Fishmanoz]

Colin, I’m not sure you have read the question correctly, or my proposed amendment to it? In order to fit any decoder, Deem has asked which wires he needs to hard wire one. I have answered that for him.

But I’ve gone further given he has a 4-pin socket already and suggested he wire a 4-pin plug to his alternative decoder, given he needs only 4 connections for decoder red, black, orange and grey. Or even fit individual pins depending on hardware availability.

[Deem]

I will be making a video with standard Hornby R7274 decoder, after that once I have received new 8 wire LiasDcc 8 pin decoder, I will hard wire it and make a video to see the difference and share with you all as well.

Regards