NN1G Mk III PCB Error

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From: Allen Jones (ajones@niia.net)
Date: Sat Aug 12 1995 - 17:49:40 EDT


Has anyone on the reflector actually built the NN1G Mk III described in
chapter 17 of the '95 ARRL Handbook?

I finally received my backordered components and finished populating the
boards Wednesday evening. Today I decided to take the RX board and mount it
to a piece of copper clad board on four standoffs so that I could check it
out and align it before pairing it up with the TX board.

When I applied power I was releaved that no smoke appeared and no hot
components were evident. The circuit was drawing about 30 mA.
Unfortunately, aside from a little hum when I touched the hi end of the
volume control, there was very little audio. I checked the LO with the
counter and it was working. I removed two turns from the toroid so that it
would tune 30M properly. I dug out my dad's old general purpose sig
generator and pumped some 10 MHz RF into the input of the RX and was able to
hear it, but it was necessary to run the level on the generator quite high.
I was able to peak all the coils and roughly adjust the BFO. Hooked up the
antenna and could now hear just a few signals very weakly.

When I first received the boards from FAR circuits I had made a few
comparisons with the ones that came with my 20M NN1G MkII from Dan's Small
Parts. The circuit had been updated and several changes were evident. One
thing I noticed was that the silkscreened outline of the FETaudio switch was
turned 180 degrees from the way it was on the earlier boards. I figured
this was just one of the many changes made to the updated board. WRONG!
After checking out the schematic and the Motorola data book it was evident
that the MPF102 was in backwards.

Out came the solder wick. Removed the FET and installed a new one the
correct way. Reconnect everything, turn on the power and, Voila! A band
full of signals and plenty of audio.

BTW, not only is the part silkscreened backward, it's also backward on the
component overlay that ARRL sends out on request. The flat on the MPF102
should face the 4.7M resistor and not T4. I'm going to call ARRL Monday so
that it can be added to the errata sheet that comes with the overlay. The
board with the error is labled "NN1G RX - 11/94" from FAR Circuits.

I can't believe this problem hasn't been discovered before. If it has,
please excuse the bandwidth.

72 . . . Allen, K9DZE


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