camman

So i am trying to use output pt6 (iac 1) to run my fan relay and i'm having some issues. No matter if the output is on or off it turns on the relay. i can manually ground and open the relay and it turns on and off. I can see the resistance go from 700 ohms to over 2 mega ohms. even at 2 M ohms the relay turns on. Is the transistor junk or do I just need to add a resistor? If it is junk what transistor is it so I can replace it?

Aaron Cake

iTrader: (1)

Are you just using the typical single 2N3904 transistor circuit? Are you absolutely sure you've connected it correctly?

Or are you using the IAC drive transistor on the Megasquirt? It's an open collector output. One side of relay coil needs to be IGN switched 12V, other side needs to connect to the IAC output.

camman

the second, the relay has power and i'm switching the ground side

Aaron Cake

iTrader: (1)

Try a different output? Perhaps that one is damaged.

Oh, you did connect the jumpers from the CPU to the IAC pins, right?

camman

Yes my problem is I can see it switching on and off with my ohm meter but even on the "off" at over 2 mega ohms it still turns on the relay.

Aaron Cake

iTrader: (1)

Your meter won't really provide an accurate measurement for this.

It sounds as though the transistor has failed.

camman

does anyone know which transistor it is that IAC1/pt6 controls?

Aaron Cake

iTrader: (1)

Here are the MS2 schematics:

MegaSquirt-II Hardware

camman

Thanks. I found the transistor I added for the fan was bad. I replaced it and it works great now.