Hello all,
Thank you for the kind words. ?I truly do enjoy problem solving. ?Every rig is like a Sherlock Holmes mystery. ?It¡¯s fun finding the culprit(s).
As I have mentioned before, I find almost all problems under my stereo microscope. ?The first thing I do with any rig that cones in is clean and scrub with 99% isopropyl alcohol. ?Then I inspect under 10x stereo microscope with bright lights. ?I find most often (in this order) cold solder joints (especially on GND pads, and enameled wire joints). ?This is followed by solder splashes, misc conductive debris and solder balls. ?Cleaning these up often solves many problems. ?Next is damage caused by accidents with scope or meter probes such as bridging 5v and 12v. ? I?rarely find a bad component (that wasn¡¯t destroyed by an accident).
Sometimes though I get temporarily stumped and have to approach a problem in different ways. ?I was fixing a QMX recently that had very low output on 10 meters. ?It was about 1 watt. ? I inspected that low pass filter under a microscope. ?The toroids looked right and had continuity, the capacitors were all in their proper places. ?The diodes were good, the 47uH inductors seemed ok. ?The lpf was selected to GND by the mosfet. ?On input to the filter, I had 5 watts in. ?On output from the filter I had 1 watt out. ?Finally after lots of staring at my scope and schematics, I pulled the entire lpf circuit for 10m out and measured each component. ?There was a bad capacitor - completely open circuit. ?I think it was destroyed in a high swr event that placed a high voltage on the cap (and a few other things as well). ?Replacing that fixed it.
The bottom line for me is patience and careful logical debugging. ?Sometimes a rig takes only 2 or 3 hours to go through. ?Sometimes it takes a dozen or more hours over a few days.
i hope this helps.
73
Jeff
W1NC
