Building presoldered peaberry

General discussion and support for the Peaberry SDR V1.

Building presoldered peaberry

Postby bfahle » Wed Dec 19, 2012 6:51 pm

I am building from the kit with the two smt chips presoldered to the board. I have gotten to step 13. Up to this point, everything has been correct, but now there is 5 volts at the collector of Q3 rather than 2.0-2.5 specified. Is this due to having the presoldered chips? I have run diagnostics which showed that pin 31 of the PSoC is connected to 5v, and that pin 32 is connected to the base of Q3 through the 100k resistor (with no power there is about 1k or 2k of resistance between pin 31 and pin 32). Is this normal for this kit, or do I have a solder bridge?
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Re: Building presoldered peaberry

Postby AE9RB » Wed Dec 19, 2012 8:12 pm

Sounds like you ruled out a short between U11 pins 31-32. The 1k resistance you measured was R15. I'm guessing Q3 isn't fully connected. Check everything in the mic pre-amp for proper values and solid connections and don't forget J3.
73 David AE9RB
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Re: Building presoldered peaberry

Postby bfahle » Thu Dec 20, 2012 4:28 am

It seems there is a short between R15 and R16. There is a normal-looking trace going straight from R16 to R15, connecting the nearest pads. However, in the schematic, there is no such connection, just lines that cross without a dot. This is P76038 V1 Rev. A. There is no other trace leading out of R15 on that side. Two traces come out of R16 pad, the one going to R15 and the one going to U11. There is no hole going through to the other side between R15 and R16 either, so it isn't an overflow of solder, it's simply a design flaw. In fact. the trace runs from R15 to R16 to Q3 collector to pin 31 of U11, so all four are connected, unlike the schematic. See the picture, especially the second one: http://imgur.com/a/Qajnq
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Re: Building presoldered peaberry

Postby AE9RB » Thu Dec 20, 2012 9:36 am

The dot is simply missing from the schematic. I'll put one there when I print it next.
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Re: Building presoldered peaberry

Postby bfahle » Thu Dec 20, 2012 1:24 pm

Ok now the voltage values make sense. It turns out if I pressed down hard on Q3 with the voltage probe, it read the correct 2ish volts, but with a lighter press it was 5 volts. Clearly Q3 was soldered improperly, so I touched up all three prongs and bingo, 2.2 volts. Thanks for your help.
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