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General Category => N Gauge Discussion => Topic started by: James320 on June 14, 2017, 01:26:15 pm

Title: Dapol Locomotive Lights
Post by: James320 on June 14, 2017, 01:26:15 pm
My apologies if this has been asked may times before, I have been asked to repair a few new Dapol locos for a friend locos who's lights are not working correctly on DC.  I model US so these are new to me. However I can't work out if it is damaged or not supposed to work? 

For example, the Dapol HST power car an dummy trailer.  On DC both loco head lights work (when traveling forwards) but the red rear lights don't.  However with a DCC chip fitted all lights work correctly (although round the wrong way).  My friend runs DC and he wants the red lights to be on as well at the back.  After doing some testing it appears to be impossible for the red lights to come on under DC as the blue wire (+ve on DCC) is only +ve on DC in the forward direction.  Dapol also apply negative to the yellow wire (which is normally the rear lights under DCC) to make the head light come on.  But as for the rear red lights, -ve is applied to the blue wire and +ve to the white which contradicts the way it works under DCC and the simple fact that LED are diodes?

Have Dapol designed this so only the full light effects work on DCC?  The same thing happens with his class 67?

Thanks,

James
Title: Re: Dapol Locomotive Lights
Post by: Only Me on June 14, 2017, 01:57:12 pm
no they work perfectly if the Schotty diode under the pcb doesnt have one side blown..... how they work on dcc and not dc is either a previous repair bodged or something else... 

actually with a dcc chip in it sounds like a short if the lights come on, its probably bypassing something and picking ac up from the track..
Title: Re: Dapol Locomotive Lights
Post by: James320 on June 14, 2017, 02:12:22 pm
Thanks, that was my suspicion.  Interestingly the lights do actually function correctly on DCC?  Sadly I cant simply pull the circuit board hard wire the lights as I know the LEDS are very susceptible to overload.  Although if I used enough resistance, some testing coming up I think.

Thanks again,

James
Title: Re: Dapol Locomotive Lights
Post by: Only Me on June 14, 2017, 02:34:23 pm
If you want to go that way, put a 1K resistor on the positive and hardwire a dcc chip removing the pcb's ... Id replace the 80p component though if you are ok soldering smt's as too much heat will lift off the track..
Title: Re: Dapol Locomotive Lights
Post by: James320 on June 14, 2017, 02:43:30 pm
I can solder it but as you say there is a risk, but as he wants DC only I will probably take the 1K resistor route and be done.  It does seem strange that both HST power car, trailing car and class 67 have done exactly the same thing.  Is this a conman problem, with Dapol stuff?  As I say i am a US N Scaler.
Title: Re: Dapol Locomotive Lights
Post by: Only Me on June 14, 2017, 03:06:00 pm
Sorry i thought you said dcc only... on dc you need the pcb or diodes to stop short
Title: Re: Dapol Locomotive Lights
Post by: robert shrives on June 14, 2017, 03:34:41 pm
Hi,
Dapol PCBs have had a few problems in the past but often thought to be a PCB build issue as soldering quality is  bit variable. some suggestion on poor components but it was a really poor batch then many more models would be affected and returns are quoted as low.

It might be worth checking max voltage output from controller and whether DC is smooth or pulsed  as a spike beyond a components capacity might just be enough and with 3 having gained same fault makes me wonder.

for the future the class 68 PCB is from another facility and does look very good compared to ones that have come before...
Robert   
Title: Re: Dapol Locomotive Lights
Post by: James320 on June 14, 2017, 03:37:38 pm
Sorry i thought you said dcc only... on dc you need the pcb or diodes to stop short

Agreed, however if I cant easily see which bit has blown I may simply build a new one using diodes to ensure always positive on the blue and relevant negative on the yellow or white filtering the positive through the working resistors on the board. (I tried convincing him to go DCC but hes not interested).
Title: Re: Dapol Locomotive Lights
Post by: James320 on June 14, 2017, 03:40:09 pm
Hi,
Dapol PCBs have had a few problems in the past but often thought to be a PCB build issue as soldering quality is  bit variable. some suggestion on poor components but it was a really poor batch then many more models would be affected and returns are quoted as low.

It might be worth checking max voltage output from controller and whether DC is smooth or pulsed  as a spike beyond a components capacity might just be enough and with 3 having gained same fault makes me wonder.

for the future the class 68 PCB is from another facility and does look very good compared to ones that have come before...
Robert   


Thanks, I have heard things like that but as most of my stuff is Kato/Con-Co/Atlas etc and DCC I have been unaffected.  At least they have solved the issue.
Title: Re: Dapol Locomotive Lights
Post by: Steven B on June 14, 2017, 03:44:52 pm
If the lights work as expected under DCC then they should work with DC. Check that all 6 pins of the blanking plug are making contact with the socket.

Try a different blanking plug from a known working loco.

Happy modelling.

Steven B.
Title: Re: Dapol Locomotive Lights
Post by: James320 on June 14, 2017, 03:50:32 pm
If the lights work as expected under DCC then they should work with DC. Check that all 6 pins of the blanking plug are making contact with the socket.

Try a different blanking plug from a known working loco.

Happy modelling.

Steven B.

Hi Steven, I tried that right away.  No problems there.  What confuses me is the DCC decoder puts out +ve on the blue wire and -ve on the yellow and white.  The LED are diodes so cant work backwards.  However in revers on DC the blue goes -ve so how does that work (or not in this case)?

Title: Re: Dapol Locomotive Lights
Post by: ntpntpntp on June 14, 2017, 05:56:54 pm
... in revers on DC the blue goes -ve so how does that work (or not in this case)?
er... never heard of a decoder doing that - it certainly shouldn't be.  Something wrong with the decoder or the board it's plugged into?

[edit]
Oh hang on - you're saying it goes negative under DC, with a blanking plate in place instead of the decoder?  Still shouldn't do that, so there's something wrong with the blanking plate (or maybe plugged in the wrong way round?).  The blanking plate should have the diodes for controlling directional lighting.
[/edit]
[another edit]
What type of dcc interface socket?  You mention a blue wire ffor function common  so I presume not 6 pin?
[/another edit]
Title: Re: Dapol Locomotive Lights
Post by: Only Me on June 14, 2017, 06:08:30 pm
Yea as i said the pcb has probably popped the 3 legged shotty diode and possibly the 2.2k resistor between the poles.. both leds are common positive so be it dc or dcc that epuld remain the same.. something is uber broken!