Bachmann USRA Light 4-8-2 DCC Upgrade

[MarkM]

I have a USRA Light 4-8-2 Item No. 81602 and installed an MRC 1650 4 function decoder.  I made no other modifications other than plugging in the 8 pin decoder (after removing the jumper).  I am using an MRC Prodigy advance DCC system.

1.  The headlight is dim, not as bright as when operating on straight DC.  What voltage lamp is factory installed?  Any thoughts on how to make it brighter?

2.  Any guidance on how to dissassemble the loco?  In particular, how to remove the boiler shell in order to access the light PCB?

[Jim Banner]

Several thoughts come to mind.  In no particular order:
 
(1) make sure there is no dc on the rails.  To do this, you may have to switch to your dc address (usually 0 or 1) and set the throttle to zero.  If the headlight is wired for half wave operation, then its brightness depends on what dc is on the rails.  I don't know if your locomotive headlight is half wave or full wave, (ie. returned to one rail, or returned to the decoder) but setting the dc to zero is easy to do.

(2) Is it possible you plugged the decoder in backwards?  If memory serves, a backward decoder will still run the locomotive but affects the lights.  Depending on how your decoder is programmed, it may have a dimmed headlight when the locomotive is backing up, and with a reversed decoder you are really backing up when you go forward.

(3) If you have extensively reprogrammed your decoder, an error may have crept in.  You might want to reset the decoder and see what happens to the light.

(4) It is also possible that you have a bad decoder that is not driving the headlight hard enough.  Do you have another decoder that you could plug into this locomotive temporarily?  Or another locomotive that you could plug this decoder into temporarily?

(5) Does your decoder allow setting the headlight brightness?  If so, it may be just a matter to changing a CV to brighten it up.

(6) When you say it is dimmer than when operated on dc, how much dc are we talking about?  If you are comparing it to the brightness you had when running the locomotive full speed on dc, then you are probably not going to get it.  H0 locomotives are normally designed for 12 volts maximum but a lot of dc power packs with put up to 16 volts on the rails.  So at full speed, the light is actually brighter than full design brighteness.  If the locomotive were not moving, there would be a chance that the heat from the bulb would melt the plastic shell.  Normally, with dc, you have motion when the voltage is up to maximum.  With DCC, you have full brightness of the light even when the locmotive is stopped and the plastic shell is not being cooled by movement through the air.  This is all assuming your locomotive has an incandescent light bulb for a headlight.  If it uses an LED or if you install an LED, then you can get lots and lots of brightness with very little heat.

As I said, just some thoughts.

[Ozzie]

Hi Mark,
I have two of the 4-8-2 s with the same sound decoder fitted.

With the decoder plugged in, in the normal manner, the lights are connected to the blue common and yes you are correct they are not as bright as when the Loco is used on DC without the decoder.

I have not considered this before ( just accepted it as a fact of life) but Jim could very well be right.
None the less I do not consider it worth the effort to change the lamps.
They do run very well and sound great... Enjoy.
Regards,
Ozzie