- I have a CRT tester and on the heater voltage setting the meter was reading way off. It was way high on the high ranges. 13v on the meter was really 12.4v at the plug. I tested a bunch of capacitors in parallel with the meter hoping to solve that. No go. But I found a 1n4001 diode in parallel with the meter made it super accurate. But that messed with my emissions reading. It was reading 180ua instead of 480ua before. I removed the diode's anode off the back of the meter and attached a wire to run over to the wiper of the 20kohm pot so it was switched out when I'm in the emission position of the mode select switch. The emissions reading went back to normal.
What I want to know is what effect does the diode have that's stabilizing the meter? Why is it working there? And what effect does the diode cause when I'm in the emissions position? Will it screw with the tester harming anything? I'll include a schematic. The diode's cathode is attached onto the back of the meter on the negative terminal. The anode has a wire running to the the wiper of the 20kohm calibration pot. That way the diode is in essence switched out of circuit when I'm in the emissions position. The meter is near the mid left on the schematic.