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MCU damaged by incorrect jumper setting

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  • dondorgram
    About a month ago I was playing around with the HT jumper on one of my OT2m s and inadvertently put it on wrong end of the jumper header. I had shorted the
    Message 1 of 1 , Sep 14, 2009
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      About a month ago I was playing around with the HT jumper on one of my OT2m's and inadvertently put it on wrong end of the jumper header. I had shorted the 12V pin to the unmarked pin below it and my OT2m went dead. On tracing the circuit the unmarked pin seems to be connected to pin 25 of the MCU (PTA5/ADC5), so I must have applied 12V to that port! The main consequence was that the MCU started to get hot.

      After an e-mail exchange with Scott, I sent the unit to him. I got it back in under 3 weeks (to Canada no less). Very fast turn around and it works once again. Scott really provided fantastic support. He also changed the EQ capacitor C2.

      Scott had mentioned that he had pulled that unmarked pin from his units to prevent that happening. I was going to drill out one of the via's, but then decided to use small diameter heatshrink tubing over the unmarked pin. Seems to work fine.

      By the way I did the same with the other unmarked pin on the lower right (under the one marked G). Don't know what it does (connected to pin 26?), but why tempt fate!

      The tubing can be removed if there might be need to access these pins at some point.

      I did not see anything posted, so thought it was worthwhile mentioning so others don't make the same mistake.

      Graham VE6GW
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