R8311 eLink DCC Controller Q1 Dual mosfet failure

[Flying Barry]

 

 

Hi all, I was looking through the post last week and I was reading the post on the “e-link fault developed” that lead me to look at what Rob had to say on this topic with the link that directed me to this web site http://www.halton96th.org.uk/page14.html

 

That made me then think about the elink that failed on me some years ago that was showing up on the computer screen with DCC short even when it was not connected to my layout but the computer recognised the com port, led light was on and would except firmware updates.

 

That then lead me to look at what was causing the track output internal short on the elink that could only possibly be the R86 3W resistor and the Dual mosfets Q1 to Q4 due to they all create heat when in operation. Checked the R86 resistor, no problem found. Removed the heatsinks from the Q1 to Q4 Dual mosfets that looked ok from visual inspection. Checked the Q1 to Q4 Dual mosfet with my ohm meter and found Dual mosfet Q1 running directly to ground (PCB/drain) with no resistance (0.00 on ohm meter) on the gate and source terminals. I then de-soldered the Q1 Dual mosfet gate and source terminals from the PCB. With railmaster running on the computer with a second elink I then removed the second elink then connected the USB and power supply to the faulty elink, no DCC short on the computer screen. I then disconnected the power from the faulty elink, connected the track output terminals to my track reconnect the power to the faulty elink and the led lights on the layout lit up so that then confirmed the only fault with this elink was the Q1 Dual mosfet.

 

I then went about locating the Q1 Dual mosfet P/N NTD5867NLT4G on the web and I found them on the web site (Google is your friend here using NTD5867NLT4G for the search) but the minimum ordered on the web site that I found was five, so I ordered them that I received last Friday. Then I went about the challenge to remove Q1 Dual mosfet drain base plate from the PCB that was completely soldered down to the PCB. The only way I could remove the Q1 Dual mosfet drain base plate was to use a dremel with a small grinding stone to remove the drain base plate from the PCB then I completely cleaned the PCB with circuit board cleaner. The next thing to do was to solder the Q1 Dual mosfet to the PCB then cleaned area with circuit board cleaner again.

 

The next thing to do was to test the repaired elink, with railmaster running on the computer and the second elink connected. I then disconnected the second elink then connected the repaired elink to the track supply, USB and power supply. No DCC shorts on the computer screen, layout led lights on so then next thing to do is to place a loco on the track. Turned lights on, lights turned on, forward movement, loco responded with forward movement and the same result in reverse. I then decided it was time to add some load to the elink that was being powered with the 4 Amp power supply. Put two Athearn PA1 A and B power units on the track and set them off that ran around for about two hours with no issues from the elink.

 

I have added some relevant pictures for the location of the R86 3W resistor and the Dual mosfets Q1 to Q4 and information for the Dual mosfet P/N NTD5867NLT4G.

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I hope this will be helpful for some that has a similar issue with their elink

 

Any questions please ask…

 

Regards

 

Barry