AMX NI-3000/3100 Bad Serial Ports

19. August 2012 Hardware 7
AMX NI-3000/3100 Bad Serial Ports

If you have worked with a lot AMX master controllers in the past, you have undoubtedly come across a unit here or there in which the serial ports have failed to function. It may surprise you to know that the fix for this is rather easy and does not require sending the unit back to AMX for repair. Below is a slightly modified document that I sent out internally at work. Please note that your mileage may vary and I accept no responsibility for any fried NI units or dead cats that may occur if you attempt the repair yourself!

Devices Affected:

Typically any AMX X000 master controller such as the NI-2000,3000,4000. However, the 1st generation NI-X100’s that are around 3 years old may also have this problem.

Why it Happens:

Similar to many devices of that age, bad capacitors were used during production. There was an era (late 90’s and early 2000’s) where bad capacitors were being produced and counterfeited in China. For more information, read about the Capacitor Plague on Wikipedia. There is a particular capacitor used on the AMX Netlinx controllers that exhibits these same issues. This capacitor is used in circuit to drive the RS-232 chips of the controller. When it prematurely fails (after 2-3 years), the voltage to the RS-232 port will decrease and not be able to deliver the specified +-10V swing. Some devices may still respond to a lower voltage which is why it may appear that not all ports are bad. Also, if there is not a lot of activity across all ports, you may not see the symptoms at all because the capacitor still has SOME storage but not enough for proper operation of all ports.

What to Do (Through AMX):

Up until recently, AMX was repairing these units even if they were out of warranty. Now however, you will be required to pay the minimum (usually flat rate) repair fee.

What to Do (DIY):

Cap Before
Original capacitor prior to removal.

The capacitor in question is component designated C155 in an X000 master and number C206 in an X100 master. They look identical and are in slightly different locations. They are the smallest cap in the cluster and I have attached pictures (before and after in an NI-3100) for further clarification. The cap used on the board is a surface mount model. However, it can easily be replace with a through-hole by simply bending the leads. The value of the capacitor used in either model is 10uF 35V for a direct replacement but a higher rated voltage should work as well. It is a very simple procedure, takes about 30 minutes from disassembly to reassembly, and costs about 50 cents for the new cap. Just make sure to pay attention to the polarity and try not to ruin the trace under the surface mount cap when removing it. It’s probably best to just snip them off and not try to desolder.


Completed repair with new capacitor.
Completed repair with new capacitor.

I believe this is a MUCH quicker and less expensive solution to get your customers back up and running in the event of a failure. It’s something that can be done in the shop rather quickly by most service technicians. I have to say that when we receive a bad master, 80-90% of the time it is related to the serial ports. I expect that we will be seeing more of this as the components continue to age so I believe this to be valuable information.




My Repair Service:

If you are uncomfortable doing this procedure yourself, and would like to send it to me for a flat rate fee, use the contact form here.


Jack is a certified AMX and Crestron control systems programmer and systems engineer. He holds InfoComm CTS, CTS-I and CTS-D certifications and has had a career in the A/V industry for over 15 years. He lives in Columbus, Ohio with his family where he works for a systems integrator serving various commercial markets.

  • Mark S

    Our controller is not powering up. Is this the result of this issue or another issue? If another issue, any recommendations what the cause may be. BTW, we had the serial port issue in the past and it was repaired around 5 years ago.

    • Not powering up would be another issue. Have you tried just changing out the power supply?

  • Prem Kumar

    Hi. can we use this capacitor which has value of around 10uF 50V kindly confirm

    • You can use a higher voltage yes. Just keep the capacity the same. You’ll have to deal with the larger size obviously.

      • Prem Kumar

        this is a capacitor, if you don’t mind, please guide me how to do this step about the capacitor soldering. meanwhile i would like to know to about the controller NI-3100 and above whether one RS232 goes defect and all other ports also go wrong is it ?

        • That’s a surface mount. It may be difficult to solder and I’m not sure of the dimensions. If it physically fits and you can solder the leads, then yeah, there is no reason it wouldn’t work. When the capacitor goes bad, you will have problems with all ports. Some devices may work with a lower voltage swing so it would likely be erratic if that is your problem. I’m not sure I can really go through the steps if you haven’t soldered before. You basically have to cut/heat the existing leads and make sure not to remove the trace. Then solder the new one in place. Tin the board leads first, set the new capacitor in place and heat up the leads again (should flow quickly). I’d pre-tin the cap as well depending on what type of cap you use.

          Good luck.

          • Prem Kumar

            HI, Thanks for your quick response. i will be back with answer once i do the test.