Dim headlioght on 4-6-2 K4 Pacific

[tmiller]

I have the Bachmann Spectrum 4-6-2 K4 Pacific. Right out of the box, the headlight is very dim. You really have to look closely to see that it is on. I recently installed a sound decoder on another similar engine, for a friend. Same problem. Having two of them with the same problem, makes me believe that there could possibly be a inherent problem. Does anyone know where the resistor might be mounted, in the boiler or on the board in the tender?

Can anyone offer any help as to what to do to make the headlight brighter, or is it a loss cause?

Thanks for the help.

Ted

[richg]

Common issue with certain Bachmann locos. The LED is down inside the loco smoke box with a plastic light pipe to bring the light up too the headlight lens. Look at the loco diagram.
Also, Bachmann uses a much higher resistor on the PC board. Somewhere around 2.5 k from some measurements I have made. Reduce the value to 1k and maybe even 800 ohms are a near standard value. 750 ohms will allow around 15 ma.
Most LED's are 20 ma max. 1K allows about 9 ma which is what many use. Parallel the resistor on the PC board or remove and put in a single resistor.
You can also put an LED right in the headlight fixture.
Notice, I did not say this would be easy.

Rich

[richg]

This is the 4-6-0 which seems to be similar.



The white dot is the plastic light tube. It is flush with the inside of the shell. It does not extend down to the LED.



Rich

[tmiller]

Rich,

The light has a yellowish tint. So is it an incandescent or LED?

I will take your advice and take a look in the tender and try and locate the resistor. That would be the easy way out. Otherwise I may try to do a replacement. Now, how much work is it to remove the boiler shell? Any surprises?

Ted

[richg]

The LED was not lit when I took the picture. It is a white LED, that I know. No idea what yours will look like when you get the proper light level.
All the components are marked on the PC boards. The resistors are only for lighting. They will be surface month components, that I know. Mine had labels for the motor leads, light leads, pickups. I used my multimeter on ohms to ring out the circuits. I have done electronic work for over fifty years so it is natural to just trace out a circuit,

If the circuit board has two green devices that look like resistors, those are inductors. A common misconception made by many.
Some just rip out the PC board and hardwire using a 1k resistor or a resistor that gives them what they like.
Rich

[Rod in PA]

Hi Ted,

My first DCC ready Bachmann HO engine was the Pennsy K4 4-6-2.  Like you, I was very unhappy with the brightness (or lack of) the headlight.  I installed an NCE DCC decoder but it did not affect the brightness of the headlight any.

After working up the courage to remove the shell, I discovered that the light was emitted through a rather long light pipe that had a 90 degree bend in it.  What I did to resolve the issue was to shorten, cut off, most of the vertical portion of the light pipe.  I did not remove the light pipe, I carefully cut it off in place.  I then bent the led up to where it was just below the remaining portion of the light pipe; this took several attempts to get the led positioned just right, but it worked.  I don't remember if the original led leads were long enough to accomplish this or if I had to replace the led with longer leads (I think I had to replace the led).  Either way I didn't have to replace any resistors and the brightness of the headlight was dramatically increased.

Good luck,
Rod in PA

[richg]

Another very good solution. For many, it would be quite a challenge. There is no simple solution, though.
Sounds like you left the PC board in place and the new decoder would have the same effect as the stock Bachmann decoder. The resistor is still in the circuit.
I can see how this happened as there are probably no model railroaders looking at the finished product to see what the headlight looks like before releasing to the production department. Engineers design and send the requirements to a company in China.
Just look at the differences in the DCC tenders.

Rich

[tmiller]

Thanks Rich and Rod for that good advice. This leaves me with a couple of options. I guess I am questioning if simply changing the resistor will do the job? That would be the easy way out. However with the design of the light tunnel, does that need to be modified as well? I would wonder what Bachmann would advise?

I am using a Soundtraxx decoder plugged into the original DCC On Board PCB.

Rod, how hard was it to remove the boiler shell? I have worked on a lot of locomotives, but never on the front end of a steamer. There are always those hidden screws, or secrets to the removal.

Ted

[richg]

Here is what the 4-6-0 looks like. The 4-6-2 might be the same.





Take some photos as you do this. A picture is worth a thousand words and can eliminate a lot of useless chatter that sometimes can be confusing. I have seen this a lot. Yes I know, some just like to chat and that is ok also.
Knowing how all the pipes fit can be a challenge so take some clear pictures to put the loco back together.

Rich

[tmiller]

Thanks Rich. That looks easy enough. Will let you know what happens.

Ted

[tmiller]

Rich,

Looking at the engine, and your pictures, there is a big difference between the two. I did find a screw under the rear truck that appears to hold on the shell, but after unloosening it, I see no movement from the body. Also I do not see any screws in the front that indicate it would hold the front part on. Looking at the exploded view doesn't lend me any help. I wonder if it is possible that the boiler shell simply snaps off?

So Rod, if you are reading this post, can you tell me how to remove the boiler shell?

Thanks so much.

Ted

[Rod in PA]

Happy Easter to all.

Hi Ted,

I'll try to explain how I removed the K4 shell, but first I'd like to say that some time after the light pipe modification, I installed a tsunami sound decoder which did not have any affect on the headlight brightness mod.

Now to remove the K4 shell.  It's been a while since I've done this but I'll give it a try.  First, look at the K4 parts diagram; it's on this web site if you don't have one on hand.  Notice the screw just in front and centered on the female portion of the engine/tender connector.  I believe this screw and friction are all that holds the boiler shell in place.

You can leave the engine and tender connected but be very careful, the connector wires can easily be pulled from their socket (that's another story).  Besides, removing the tender is a lot more complicated that removing the shell.  I use a thick, folded up bath towel to work on; you can roll the engine from side to side or upside down without having to pick it up.

Now back to the screw behind the connector.  There should be just enough room to back out that screw without having to remove the female connector, if not you'll have to remove the connector (just two screws).  Once the screw is removed, roll the engine back up right, lift up on the cab portion to about a 30 degree angle, gently push the entire shell forward (the bottom of the smoke box hooks onto the weight), the shell should now be free.

I hope this helps, let me know how you make out.
Rod

[richg]

I strongly suggest disconnecting the loco and tender when you have to work on them. Very easy to do. Below is what I do. I gently pry the plug up a little with a small jewelers screwdriver.



The Bach-Man and some others use a tool from Micro Mark. Search the General and HO forum back about three weeks. Someone here already asked how the connectors can be removed without damage.
In a hurry or impatient usually results in a damaged plug/wire.

I use a foam cradle from Bowser trains for working on locos, tenders and rolling stock.

Again, a different decoder will not result in a brighter LED because the resistor in on the PC board.
My locos had as many as three resistors on the PC board for one headlight. Bachmann does like variety.

Rich

[tmiller]

Hey Rod,

Got the shell off. Easy when you know how. I did remove the two screws for that hold the connectors in place, in order to remove the screw holding the shell.

The LED is a small one mounted to a circuit board, so it appears that there is no way to bend it upward like you mentioned. I am assuming that the LED fits close against the plastic light tunnel? I did power up the unit and the LED seems to be very bright, but by the time the light makes it's way up the tunnel, then the 90 degree turn, much of the brilliance is lost. So, I am thinking of a couple of options. One would be to leave well enough alone, and live with what I have. The other option would be to replace the current LED,  and cut the light tunnel away inside the shell as you said. However, I would want to see if a different LED would be any brighter. If it isn't brighter, would removing part of the light tunnel, pointing the LED upward to the tunnel,  make that much difference?

Stuff to ponder. Happy Easter.

Ted

[tmiller]

Rich,

Yes it best to disconnect the tender. Yours, as I see in the picture, has the standard drawbar, the K4 has the wishbone type drawbar. I would prefer your type.

I do use the foam cradle as you suggested. To many disconnects could lead to a damaged wire. "Carefully" is the word when plugging and unplugging.

Ted