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Dapol Class 121 Head Code Lights

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  • Andy Dapol
    commented on 's reply
    Glad to hear you've sorted it to your satisfaction!
    The many variations is one reason I am slowly trying to standardise where possible. Hopefully your notes above will help others with similar models.

  • Paul-H
    replied
    Thanks Andy

    Mine is wired quite different to the one in the picture, on mine the pairs of brown wires are soldered to the pads with the white wires, unless the picture is showing them after they are moved but on mine the outer pads have the red and black wires from the track.

    In the end I took the easy route as all I wanted was the headcode to come on at one end as it was being pushed backwards by the motor unit. to achieve this I disconnected the two blown LED wires at the pcb and moved them to the top of the PCB were pads are available for a direct connection to the decoder, so I connected the LED Anode to pad 3 and the Cathode to pad 5 via a 1K smd resistor.

    Its now working as I need it.

    Thanks for your help with this.

    Leave a comment:


  • Andy Dapol
    commented on 's reply
    Apologies the article was intended as an aide-mémoire for engineers, I have added the photo to my reply above which completes the note.
    Unfortunately there were many versions of the PCB before it was standardised as a next-18 socket type and some further confirmation of the connections would be required.. Difficulty in access is, sadly not something I can assist with remotely. If you have doubts in being able to carry out the work, I suggest that you either return the model to your dealer or contact DCC Supplies who would be happy to carry out the work for you (you will need your proof of purchase).

  • Paul-H
    replied
    Thanks for the reply and instructions Andy
    NO sign of the instructions on DCC supplies knowledge base, can you post a direct link as the pictures would be a big help.

    Had a quick look at the wiring under the PCB and noticed a couple of things, first the mention of 4 unused solder pads, mine only has 3, the second regards the instructions to cut two brown wires then if those don't work cut the other two, the problem with that is once the first pair of brown wires are removed it's going to be almost impossible to reattach them to the PCB because of the lack of room or access to the pads they wire first soldered to.

    So seeing the photos is important before I end up with no lights at all.

    Thanks

    Leave a comment:


  • Andy Dapol
    replied
    Hi,
    There is a knowledgebase article on DCC Supplies helpdesk which may help regarding this:

    N Gauge Class 121 or 122 Lighting Fix
    Posted by Fiona F. on 25 April 2017 03:58 PM
    If you have an old style N Gauge Class 121 or 122 (6-pin socket), which has an issue with the head code lights, here is a fix for you to carry out to correct this.
    • On PCB, cut one of the brown wires on the soldering point marked R1 connection (brown that goes to the front of the loco with the exhausts, and is the shortest brown)
    • On PCB, cut one of the brown wires on the soldering point marked R2 connection (brown that goes to the back of the loco and is longest brown)
    • On PCB, there is a group of 4 unused solder points, join the 2 wires and solder them to the bottom right soldering pad. see picture attached
    • If lighting is wrong way around. Try the other 2 brown wires on soldering pads R1 and R2.
      NB: The easiest way we have found to do this is first look at the model with the front of the model (exhaust end) facing away and keep it in this orientation. Your will then find the brown wire leading to the left hand side of the LED which comes from the R1 soldering pad and then the brown wire coming from the left side of the LED to soldering Pad R2.
    Click image for larger version

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    Be aware to see the lighting wires you will need to remove the seating first.
    Last edited by Andy Dapol; 2 February 2021, 14:57. Reason: Added photo

    Leave a comment:


  • Paul-H
    replied
    Sorry I know this is an old post but I am also having the same issue with a new class 121 just received which must have been old stock in the shop as it was the 6 pin version, what decoder did you eventually fit to get the directional and headcode lights to work correctly.

    Thanks

    Leave a comment:


  • Roy Whitgrove
    replied
    Originally posted by Jeanette-H View Post
    Hi all

    I have just taken delivery of a new Dapol Class 121 and have something I want to check

    I have found the head code LED's although on are quite dim and do not show once the roof is clipped back on, even with all the room lights off, is this normal for this model, not a problem if it is but just wanted to check.

    Thanks
    i
    i had the same problem, I switched decoders, if I remember right I’d bought a loco together with a Gaugemaster decoder, switched them round and the headcode boxes work fine and the directional lights.

    Leave a comment:


  • Roy Whitgrove
    replied
    It’s awhile ago since had a problem with these LED’s and I’m not at home to check my facts, but I seem to remember that the Zimo decoder did not work but when I swopped it for a Bachmann decoder it was perfectly ok.

    Leave a comment:


  • Jeanette-H
    replied
    Following some advice found elsewhere I have checked how you have engineered the connection and power of the headcode LED's and found the following

    Both Headcode LED's are connected together and only powered from pin 5 on the decoder which is power for the white Headlight LED's so in theory when either white headlight LED is on the headcode LED's should also be on, but as they are not on all 4 of my brand new models supplied by 4 different ebay model rail traders I can only assume that the two headlight LED's are not directly connected together but go through some sort of passive device which is stopping the headlight at one end from illuminating the headcode LED.

    I have yet to find anyone through many internet searches that can confirm the headcode lights work any different to how mine work, so its obviously a fault in the design of the lighting circuit.

    None of the above explains why on the Gaugemaster Decoders work the headcodes, with no headcode at all with Zimo, Bachmann (Pre Zimo Version) and LaisDCC who also supply your own Imperium decoder.

    I don't expect a meaningful reply to this but let it be a warning to others thinking of buying either the class 121 or 122 from yourselves

    Leave a comment:


  • Jeanette-H
    replied
    Unfortunately all from the well known auction site, but all 4 with the same issue? that sounds like something has gone amiss in production rather than a random fault

    Can anyone with either of these models confirm that your head codes are working and what decoder you have used. Still don't understand why they appear to work with the Gaugemaster decoder but not with any of the others!

    Perhaps someone in Dapol could check a couple of stock items in case its a bigger problem than my 4

    Leave a comment:


  • Andy Dapol
    replied
    Hi, Actually it should work with any of these decoders. Since the model is new I suggest its reasonable to return it to your dealer for replacement. If this is not possible or undesirable for some reason, then contact our service centre DCC Supplies 01905 621999, who will be happy to repair it under warranty. The only exception would be if it has been purchased from a private seller or via an auction site of course.

    Leave a comment:


  • Vonzack
    replied
    What does it do on DC with the blanking plug in place. Reason I ask, is that the 122 and 121 take a 6 pin chip, so the Headcodes must be driven from the F0f and F0r connections. All the chips mentioned supply these yet you get different results. Maybe the issue is voltage / current supply from the chips and it just so happens that the DCC23 is in some kind of sweet spot.

    Just a thought and hope you get it sorted.
    Last edited by Vonzack; 6 December 2018, 09:37.

    Leave a comment:


  • Jeanette-H
    replied
    Just by way of a heads up, I have been playing around with decoders in these models and found the following.

    this is with the models used as said above, power unit and dummy placed exhaust end to exhaust end, and is the same with Class 121 & 122.

    with the following decoders, Zimo MX622N, Zimo MX616N, Bachmann 36-558A and Laisdcc
    860013, you get motor control and head and tail light control but no head code lights

    But using the Gaugemaster DCC23 I get motor control, head and tail lights and head code lights but only on the unit at the front, whichever direction it is moving.

    so two questions

    Is it correct that the head code lights will be only on in the unit at the front, how does the one st the back know it's at the back

    why do the head code lights only work with the Gaugemaster decoder?

    thanks

    Leave a comment:


  • Jeanette-H
    replied
    Not sure if I have solved this or not, but after googling around i have found that the exhaust end is the rear, so if I mount the 121 & 122 rear to rear I now have the head code LED's on at the front when travelling forward then on at the other end when travelling the other way, so head code is illuminated at the front of the loco, still dont know if this is how its supposed to work but its a sort of work around. so may be of use.

    Perhaps someone from Dapol could confirm what I have found is how they were designed to work.

    Thanks

    Leave a comment:


  • Jeanette-H
    replied
    Ok so now I have a Class 122 driven unit and a class 121 dummy, both with the same issue, when travelling exhaust end first neither head code LED illuminates bright enough to be seen in a darkened room but when travelling backwards non exhaust end first the head code LED are bright enough to see with the room lights on.

    Perhaps I am misunderstanding something fundamental with these, which end is the front, exhaust end or non exhaust end?

    Leave a comment:

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