R2701 HST dummy lighting problem

[NorthPolePete]

Hi - I have an R2701 HST set that I've put the DCC tts chip into - the power car works fine, but the dummy car runs but the rear lights weren't illuminating. I took the dummy car to bits and found the terminals on the board that ran to the lighting board. I could make the white LED light up by connecting straight to the mother board, but the red light just flickered when connected. I purchased the X9872 dummy car replacement lighting board, but couldn't get any lights to stay on when manually connecting them to the main board. The voltage coming out of the board for the active light was 20V DC and around 7V DC for the inactive light. When the unit is reversed the 20V slowly drops down to 7V and the previously 7V connection goes up to 20V. Would anyone know whether this is the correct voltage for the lighting boards, or suggest anything else I can do to pinpoint the problem? Thanks in advance. 

[96RAF]

The main pcb has onboard resistors that protect the leds so if you by-pass the board the leds will likely be zapped.

 

A decoder is not going to put out any more than 12v DC on the blue wire, the white, yellow, green and purple (if exists) are switched negative returns. Your readings do not compute.

 

I can’t see why you thought changing the main pcb was going to sort the problem as these are fairly reliable.

 

Is your dummy car motorised or just a trailer. You say it ‘runs’. The likely problem was the trailer car decoder just needed its directionsl logic reversing or the decoder may have been fitted 180 degrees out Which prevents the lights working at all.

 

I’m afraid your repairs may have made things worse.