Solar Shed Update

 

As I explained in the previous post on the Solar Shed, I redesigned the PCB, since the HPC Curiosity Board was consuming too much power.  My plan is to build this in phases (which was a good idea as explained later).  These phases will be and probably in this order:

• DC-DC converter
• 3.3 VDC LDO
• PIC processor, buttons and LEDs
  
• LT1085 LDO
• Relays and FET drivers
• ADC Input
• Misc

Once the first three are done, I will work on getting the PIC firmware running.  May have to fake the ADC inputs, but that is OK.  Really all I will be trying to do is ensure the PIC runs and the buttons?LEDs work.  Once that is done, then the rest should go very quickly.

No Power

Following the list above I built the DC-DC converter section.  I literally took the design from the train LED controller, which works, and placed that design on this PCB.  Well there was no 5VDC.   My first thought was that the resistor divider network was in backwards, ie somehow the reference designators had not been placed correctly during PCB layout.  I measured the resistance in circuit, which is always iffy, since there is no way to see what the equivalent circuit really is.  The 20K measured 16K and the 120K, measured 55K.  So I pulled the 120K and replaced it with a 110K, that was in the original design.  Still no 5VDC.

Nothing was getting hot, the converter just wasn't starting.  I poked around with a DVOM looking at the voltages everywhere, other than no output voltage nothing seemed wrong.  Touched up most of the small solder joints, just to make sure they were connected, even though the DVOM showed connections.  Then did continuity checks where I could, still nothing.

 

Then I carefully looked at the inductor.  These can be hard to get the solder to flow onto the connections.  The picture shows what should be sufficient solder, but these are Lead Free, thus that is silver solder and will need more heat to flow properly.  Plus I didn't help the issue by using the very small tip on the Metcal Soldering Station.  I changed to the bigger tip (see picture below) and reflowed both connections on the inductor.  And that solved the problem😊.  Note to self, don't take short cuts, especially with the inductors and any parts that have silver solder on them already.

 

Installed the 3.3VDC LDO and the 3.3VDC came right up.  So I am ready to move on and install the PIC processor and related items.

This is why I try to build these in phases.  I have lots of experience building these types of boards by hand, but things happen.