I had difficulty with the Unified Microsystems BCD-14, i.e. the CMOS inverter IC was overheating.
I eventually received the following advice from AB3CV, which I found to work. -John AC6SL From: Jim Miller <j...@jtmiller.com> Date: Sat, Dec 26, 2015 at 7:06 PM Subject: Re: [Elecraft] K3 and Band Data To: John Nogatch <jnoga...@gmail.com> My BCD14 purchased this summer was unreliable as well. If you look at the K3 (or K3s...the same) the Band Data outputs are open collector pulled up by 2.2K in series with 200ohms. I knew this could be a problem with anything which wasn't properly buffered so I looked at the BCD14 schematic. I found the BCD-14 online schematic differed from the unit I had after inspection with a ohm meter and magnifying glass. I probed my unit and found the optoisolators on my board had a current transfer ratio insufficient to drive the decode chip input to a proper logic low level when used with its supplied collector resistor and driven by the K3s' modest pull up. After some discussion with the supplier I changed the collector resistors to 33K and it works perfectly now. The dark current on the optoisolator and the input bias current on the decoder are insignificant making this resistor change possible. The improper logic levels on the board could easily result in operating in the linear zone and oscillate as a result. Good luck jim ab3cv ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
