Senario:
A functioning toy locomotive powered by 3(AA) batteries producing 4.5VDC to this IC board.

Topic:
Can anyone explain to me how I'm receiving a short indicator from my multimeter between the bottom of the 164 resistor coming off the base of Q3 and the bottom of the 104 resistor? (Upper left hand corner of photo.)

I took a photo of my multimeter and the two resistos with back lighting. One photo of the IC board is from the SMD side, and the other is from the THT side.

On either side, I see no leads running between the two resistors. But when I check with my multimeter it indicates a short, but when I run a voltage check, I get 2.3VDC at the bottom of 164 leading to Q3, and 4VDC at the bottom of 104.

How can one have a short between two different components and two different voltage levels as well?

I know the answer is simple, but I can't explain my reading and my observations.

Thank you.

 

Just a bit of quick terminology -

If the SMT resistor has three numbers, it's going to correspond to the traditional thru-hole resistor coding, so 164 = 160K and 104 = 100K. The side of the board with the thru-hole parts is the 'component side' and the bottom side would of course be the 'solder side'. Just to make it easier when others eventually step in to help you.

Looks like the board picture is cropped tight to or off at the bottom? What are the numbers on Q3?

 

Did you remember to remove the batteries when you took the resistance measurement?

 

Just a bit of quick terminology -

If the SMT resistor has three numbers, it's going to correspond to the traditional thru-hole resistor coding, so 164 = 160K and 104 = 100K. The side of the board with the thru-hole parts is the 'component side' and the bottom side would of course be the 'solder side'. Just to make it easier when others eventually step in to help you.

Looks like the board picture is cropped tight to or off at the bottom? What are the numbers on Q3?

Thanks for that information, the Q3 is a 8950S.

 

Did you remember to remove the batteries when you took the resistance measurement?

With the batteries removed, there's still a short between the 16K and 10K resistors.

I thought to measure the resistance of a component on a IC board, you must first remove the component from the board to measure its resistance or the multimeter might just read a lesser resistance of a component in parallel somewhere esle on the board.

How can a person read a short between these two seemily unconnected resistors and yet have two different voltage drops.

 

If you follow the traces on the side with Q3 showing, you will see that one lead of Q3 goes down to one cable.
The lead from the positive terminal of the upper capacitor goes down to another terminal.
You need to follow to where those wires lead.

 

If you follow the traces on the side with Q3 showing, you will see that one lead of Q3 goes down to one cable.
The lead from the positive terminal of the upper capacitor goes down to another terminal.
You need to follow to where those wires lead.

That's it MrChips!!!! Great job. The base of Q3 traces back to the terminal of the GREEN wire at bottom of the IC board, and the positive lead of C7 traces back to the terminal of the BLACK wire at the bottom of IC board. Both BLACK and GREEN wires connect to the DC motor (short found). See photo with C4 standing up.

Thanks for the help, but could you explain to me the differance in the voltage, when the DC motor is turned on (2.3VDC at the bottom of 16K resistor and 4VDC at the bottom of 10K resistor).

Does the operating DC motor provide some type of electrial barrier so that the two voltage can develope?