Fuel Pump Always On?

[woznaldo]

Ok, i'm still not sure where in the driver circuit the fault lies, but here's what I've got.

Using a DVM with ground on the neg terminal of the Stim power supply terminal block, I measured voltage in several places around the circuit. The Q3 transistor was fitted and the processor was removed.

- between D7 and Q3 collector: 4.1V
- between D7 and D14: 12V
- between R13 and Q3 base: 1.08V
- at Q3 emitter: 8.1mV
- at pin33 on U1 socket: 1.08V

Also took some resistance/continuity measurements.

- across R13: 1Kohm
- across D7 (pos on Q3 side): 2.4 Mohm
- across D7 (pos on D14 side): O/L

Then I cut the base leg of Q3. I connected MS to the car and powered up. The fuel pump came on.

I than cut the collector and emitter legs, but left the remains in the board and again connected to the car and powered up. The fuel pump did NOT come on.

I have checked for continuity between the severed legs of the Q3 transistor going through the board and they were all O/L?

[woznaldo]

I was told that the pins on a TO92 can only be in one of two configurations. This is obviously not correct! The emitter and collector are in opposite locations to that show in the assembly manual!

Problem sorted, but now worried that Q5 may be in backwards?

[billr]

let's see if this works:

http://www.learnabout-electronics.org/S ... ations.jpg

Not only does the TO92 not have any specified pin-out, but there are other packages that look quite similar.

[woznaldo]

let's see if this works:

http://www.learnabout-electronics.org/S ... ations.jpg

Not only does the TO92 not have any specified pin-out, but there are other packages that look quite similar.

I think the version I have must be the Motorola type as it ties up with a safety data sheet I found on Jaycar's website? It doesn't tie up with any in the above document?

[DaveEFI]

That's why I asked if the new was identical to the old. Does your DVM include a transistor tester? They show transistor gain, and won't if connected wrongly.
You can also buy ones cheaply these days that not only show gain etc, but also show on the display which pin is which for an unknown one.

[woznaldo]

That's why I asked if the new was identical to the old. Does your DVM include a transistor tester? They show transistor gain, and won't if connected wrongly.
You can also buy ones cheaply these days that not only show gain etc, but also show on the display which pin is which for an unknown one.

Dave, I think I must have missed the question or thought I'd already answered. Apologies.

I think one of those testers sounds like the way to go. Would have saved a lot of heartache!

Thanks to all that have helped me resolve this issue, especially Dave who has been very patient!