Model Railroading > Lights blow adding DCC/Sound to ATH Genesis Yellow Box

Hi Everybody-

I recently added a TSU-PNP8 Decoder to an early DC only Athearn Genesis Yellow box SD70M.

After getting the shell off I removed the stock DC board. After popping in the new board, I connected +/- for the motor then the front/rear pickups.

After reading the card that came with the TSU decoder, I went to their website and found the proper wiring diagram for connecting 1.5v bulbs. 

I connected it exactly like the diagram and all 6 lights, 2ditch/2 head 2rear,  got really bright then burned out when in forward or backward running direction.

The diagram only shows a resistor when using LED but none for the 1.5v. 

I'm thinking I might need a resistor along with 6 new 1.5v microbulbs. If this is the solution what size resistor should I use?  

Thanks for looking- Rob

 

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If you did connect the front and rear lights so that one side of each light went solely to the positive common on the side of the board, then it should have worked. But use a multi-meter to measure the voltage from the negative connections on the ends to the positive on the side to see if it reads 1.5v

Ted Curphey
Ontario, OR

Athearn has available the LED's made to fit into the headlight openings.    Convert to them.

Richard.

Update-

I brought my Fluke 86V home from work and got these readings.

Voltage across V1 (1.5v) and No.3 (Headlight) I get 0v.
Voltage across V1 (1.5v) and No.6 (Backup) I get 3.65v

I'm thinking this decoder has something wrong with it, but to make sure,  I'll remove the wires for the bulbs when I have some time tomorrow and see if the readings change.

Thanks for the reply Ted and Richard I'll look into the LEDs as I already have a few 1k resistors for that change if I go that direction.

Rob in Fremont
 

I'm wondering if your actually have the board that's in the duagram. Measuring from V1 to either pin 3 or 6 should get you 1.5 volts. 3.6 is more of an LED voltage. Pulling the dead bulb wiring and cleaning up the contact pads is a good next step. It will be interesting to see what you find.

Update 2-

I removed the 1.5v micro bulb wiring and got these readings with track pickup and motor leads still connected:
V1 (1.5v) to pin 3 (Headlight) with direction in Forward = 2.07v
V1 (1.5v) to pin 3 (Headlight) with direction in Reverse = 2.94v        **This should be 0v**

V1 (1.5v) to pin 6 (Backup light) with direction in Reverse = 3.20v
V1 (1.5v) to pin 6 (Backup light) with direction in Forward = 1.83v     **This should be 0v**

When I double checked the decoder, to make sure the type matched the diagram, I got TSU-PNP8F on the reverse side of the decoder. The schematic is TSU-PNP8 with NO F. The Soundtraxx website doesnot have a diagram with the "F" on it so I assume the diagram is correct? 

At this point I think I'm out $90 bucks for this decoder and will pick up another this weekend. The sound and throttle all work as expected though.

Anyone have any other Ideas?

Thanks,
Rob in NorCal

Rob, contact Soundtraxx. They are helpful. If your decoder is defective and isn't still under warranty, you can get it repaired for $45.00.