Temperature controller: Testing, known bugs and fixes

• The values of R16 and R17 printed on the PCB are the wrong way around: R17 should be 90k9 and R16 should be 10k. Looking on the schematic these resistors set the voltage across the resistance bridge network: Without this fix the voltage across the bridge is 1V, not the 9V it's meant to be.  We are also replacing R16 and R17 with precision (10ppm) resistors to add stability to the resistance bridge.

• The July 2000 version of the board has a short between the -15V power supply track and ground. At the power supply connector, J5, the pad for the -15V is in contact with the GND track on the bottom layer. Additionally, the negative pad of C2, which connects to -15V on the top layer, is touching against the GND track on the bottom layer. Correcting for these errors removes the short.

• Also in the July 2000 version, the track from the top pin of R4 to pad 3 of J6 contacts against pads 1 and 2 of J6 on the bottom layer, shorting across the set point variable resistor. To correct this, either cut the track between pads 2 and 3, and between pad 1 and the resistor pin, then rewire from the resistor to pad 3, or cut away the top sections of pads 1 and 2 on J6 on the bottom layer to isolate them from the track. Pads 1 and 2 need to remain shorted, but isolated from pad 3 and the resistor.