Monday, December 28, 2009

On the rocks

A disappointing day in the G4ILO shack. I did some more work on the SoftRock 6.2 Lite kit which I was hoping to make into a panadapter for my K3. But the project has hit the rocks as the local oscillator doesn't work and I don't know what to do about it.

I started off by adding the components for the regulated power supply. That checked out fine - not much to go wrong there, really.

Next I built the crystal oscillator part of the circuit. That also worked fine - I could hear a strong signal just below 32.768MHz on my FT-817 receiver.

The stage after that was the divider circuit, which is supposed to divide the oscillator frequency by 4 to give the 8.192MHz local oscillator required by the K3 version of the SoftRock. I didn't need to add any components for that, as I'd already soldered in all the SMT components and this stage just involved adding the divider ICs. So I tuned down to 8.192MHz and heard nothing.

The current consumption of the SoftRock was correct for this stage, but some of the voltages on pins of U2 were not correct. There was zero volts on pin 2 where there should have been a reading. I checked the board carefully but I could not see any solder bridges or anything else I have done wrong. I don't have an oscilloscope so I can't see what is happening.

I don't know what is wrong, and I don't know what to do. Perhaps it was a mistake to solder all the SMT parts first, but I really would not have liked to do it after the through-hole components were added, making access difficult. Perhaps my anti-static precautions weren't good enough. I did use an anti-static mat and wrist band, but I'm getting pretty absent minded these days and there were times I forgot to connect the ground strap to the wrist band before handling the board.

I don't have any replacement divider ICs to try, and to be honest I find the board too small to work on. I doubt that I could remove a chip without lifting the PCB pads at the same time. I don't know why the SoftRock couldn't have been designed using all through-hole parts with socketed ICs, on a larger board. It doesn't appear to use any components that aren't available in leaded versions, and it would have made the project easier to build and easier to troubleshoot for most people.

The SoftRock has gone into the box of projects that didn't work, along with my short-lived enthusiasm for SMT construction.
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