FT-991A Enhanced COM port problems

Discussion in 'Radio Circuits, Repair & Performance' started by KN4ZXN, Apr 24, 2020.

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  1. KN4ZXN

    KN4ZXN XML Subscriber QRZ Page

    Hello Everybody,
    I've been tinkering with my 991A to perform PY2RAF's panadapter mod and in so doing, I think I accidentally messed up the Enhanced COM port. Other than this particular issue, everything else in the mod works amazingly.
    Symptoms:
    I am able to send CAT commands through a terminal to the Enhanced COM port and the radio responds accordingly (i.e. changing frequency), but when sending a command to read back any information (i.e. reading current frequency), the radio doesn't respond. These commands work both ways when using the RS232 port, but unfortunately not all CAT commands work on that port. The big downside to not being able to receive back on the enhanced COM port is that my RTSystems programming software doesn't recognize the radio. I also cannot reprogram my firmware as that also requires some sort of response from the radio. Before the mod, the Enhanced COM port was working just fine. I've tried replacing Q1008 CP2105 USB-to-Serial converter, but the issue is still there with the exact same behavior. I have another one just in case I need to replace it again, but I'm really hoping it doesn't come to that.
    I think my next step is to probe the ferrite beads at the ribbon cable that leads to the control unit and see if anything comes back on the RX line. If not, then it seems the issue is upstream, either in the ribbon cable or the control unit or there is a short on the RX line to ground, but if I do see a response, then I will have to trace it back and see where the discontinuity lies. Is this my only recourse, or is there an easier check that I can do before that?
     
  2. KN4ZXN

    KN4ZXN XML Subscriber QRZ Page

    I haven't opened up the radio again yet, but after spending some time thinking about the problem, it occurred to me that the only part in the path of the RX line that was continually messed with during this modification was the repeated removal and insertion of the ribbon cable. It is possible that the cable could have been compromised. Again, this is something I'll have to check.
     

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