These three board units are Snapon MT2700 high voltage test meters for measuring spark plug high volts using neon bubs with variable resistor. The pots were tested OK. There is small power circuit and led using input 9v battery. None of the 3 same boards registers high voltage.

 

OK, we see three circuit board assemblies that we have no hint of the theory of how they work, no way to check voltages, and no hint as to how they are used. And we only get to take a look at the component side of one of them.

How much assistance can we get from the TS as to measuring voltages?? And checking stuff??

 

OK, we see three circuit board assemblies that we have no hint of the theory of how they work, no way to check voltages, and no hint as to how they are used. And we only get to take a look at the component side of one of them.

How much assistance can we get from the TS as to measuring voltages?? And checking stuff??

I purchased 3 used units as for measuring high voltage on spark plugs. None work. The variable pot sets the range for led to come on at level. There is a visible "NEON" bulb on all units. The input high volts has to go through it. The 2 leds are ok and the pot. Should I assume the neons are all bad? This is a capacitance clip pick up of high volts from the plug cable,- not direct connection. This type of meter is what was used in auto garages before switching to large oscilloscope or the hand held small scopes with probe voltage divider protection.
On another note, I had fixed several people's timing lights as they had put power clips on wrong bat terminals and charged up the main capacitor backwards. No flashing with wrong polarity. Some consumer products have diodes on input for the stupid people.

 

Consider that MOST IC failures do not result in anything visible, such as discoloration or signs of overheating. Likewise, a capacitor that has short circuited will not show visible damage unless there is enough power available to allow heating.
Besides that, If a resistor has overheated and burned, it was some other component that caused excess current. So visual inspections are mostly useful for spotting failed solder connections, or corrosion problems. If we can see the circuit, some folks are abe to see which components may have been over stressed and should be tested.
Is tghere any way we can see the circuit???