Tuesday, September 14, 2010

Lots of resistors and the thermistor board

I've completed installation of lots of resistors and a few resistor networks on the front half of the RF board. The last several steps of this were devoted to construction and installation of a small daughter board, first introduced in 2003 (as far as I can tell), which replaces RP3 and provides temperature compensation to the PLL, thus greatly reducing warm-up drift.

Here's the daughter board. It's quite small, occupying a space only slightly larger than an 8-pin resistor network. It in fact is installed on the motherboard in the same space as the original RP3. It was a bit tedious installing the 8 leads; I ended up doing the 90° bend first, then taping the lead down on the component side, and then soldering it in place.
Here's the thermistor board installed in the front left quadrant of the RF board.

It looks like getting C87 and RFC14 installed without shorting out to the back of the thermistor board will be difficult. Postings to the K2 forum all say "don't worry, it will all fit", but I think it may be necessary to put some electrical tape on the back of the thermistor board. It also looks like spacing for Q19 will be very tight. The instructions talk about checking to make sure that the thermistor board isn't shorting out to other components; this is not helpful at this point because the components haven't been installed yet!

For those keeping track ... just completed page 50.