Wednesday, May 21, 2014

Minima - VFO Troubleshooting - Cont'd 3

After four days of extreme frustration, while troubleshooting my Minima VFO Module (see previous posts), there is success!

My friend Jeff - KO7M came by today with known working tools (BusPirate) and parts (Si570). We had been troubleshooting my VFO problem via e-mail and over the phone, but we were not getting anywhere.
Jeff at the Microscope
The problem came down to, two (2) simultaneous failures, one in my BusPirate (BP) and one in my VFO Module that I was testing.

1. My BusPirate fails to generate I2C SCL (clock) signals, even though many other functions seamed to work. Without an SCL signal data can not be received by a Device Under Test (DUT), even though the BP can receive Data using the same SCL wire from the DUT.

2. The failure of my VFO was the Si570 itself, it would not accept I2C data or commands, even though it produced RF on the output. It is DEAD.

Before Today

Before today, I had created an Si570 BreakOut Board (see previous post), with just the Si570 and Header pins. My intent was to verify that the BP was working as expected, but because there are also wires, clips and connectors that could have failed results were inconclusive.
Si570 Breakout Board
Si570 Breadout Board
At this point I still could not determine if the failure was in the BP or had I damaged another Si570. So, I built a second Si570 Breakout Board. But alas, still nothing seemed to work.

Today - Jeff to the Rescue !

With Jeff's known working BP we quickly determined my VFO Module (i.e. Si570) was bad. Other I2C devices; the two Si570 Breakout Boards and a Real Time Clock Module (RTC) all work as expected.

Because yesterday I had used my last Si570 on the second Si570 Breakout Board, I could not repair the VFO Module. but we could build an Si570 Breadout Board Adapter  that connects between the Breakout Board to the Minima CPU Module. I had previously designed and did a layout for the Adapter with DipTrace, for just such an occasion. We spent the rest of the afternoon building and testing the Adapter Board.

The Adapter Board tested correctly with Jeff's BP as we hoped. It also tested and worked with the Minima CPU Module.
Adapter Board Connected to the Minima CPU
and a Coax Cable, the Si570 Breakout Board in the Foreground
Stacked and Ready for Testing
Now all Minima Modules worked as expected, we checked for a varying frequency while tuning, we estimated on the oscilloscope 20MHz at the low end, and 50MHz and the high end while Tuning across the (0-30MHz) HF band (for a 20MHz IF).
34.2MHz  (14.2+20) As Shown
with 10X Expanded Sweep Scale
Minima CPU Module and
Temporary VFO Module 
I am a happy camper - Thanks Jeff, for the help !

I can now continue my experiment Minima Transceiver Project.

I need to order a few more Si570's, and a new BusPirate (or troubleshoot and fix it).



  1. Happy to help anytime. Let me take a crack at the bus pirate debugging if you like.