Phase 1: Power regulator, bypass capacitors etc

Phase 1 according to K7QO's build document is the power regulator and the surrounding parts. He has also included a couple of bypass capacitors that sit on the 8v line.

  • J1 – power connection
  • S1 – power switch
  • C43 – 47nF cap
  • C42 – 10μF electrolytic cap
  • U5 – 78L08 voltage regulator
  • C54 – 47nF cap
  • C8 – 47nF cap
  • C41 – 100μF electrolytic cap
  • D7 – 1N5817 or 1N4004

Once these are soldered, I used a 9V battery and powered it up and can get around 7.7v on the output of 78L08. The voltage is a bit less because the 9v has a 0.7v drop and so the input itself is pretty low. I guess once I give ~12v input, I should get a neat 8v output.

parts soldered

Now for some interesting debugging..

The power berg pins has a leg that connects to the ground and the ground copper is at the top. When I connected the battery, power wasn't coming at all. This was because the jumper was covering the top pad and I could not solder them in. I had to melt some plastic to access the pads and solder it to the pad.

melted power socket to access the ground pad

The voltages at U1's pin 8, U2's pin 8 and U3's pin 6 should also be on the same 8v rail. When I checked, U3's pin 6 was fine, the rest were not. Also, one of the legs of C54 and of C8 is on 8v line too. But they were not. After some head scratching, I figured out that it is because of the lack of vias on my PCB. I seem to have an early version of the PCB and the vias are not connected. After a bit of tracing, I figured out that on the bottom right part below R3 and to the right of C50 is a via.

the unpopulated via on the bottom right

I quickly soldered a resistor leg into that and soldered the top and bottom. (not shown in the photo)

Once that is done, the trace that leads up to Q8 gets the 8v. Once Q8 is populated, and the via soldered on top and bottom, the other leg of C54 would get 8v as well and also the U1 and U2 pin 8. Problem solved...