P&H board v1.1b INJ4 constantly switched on

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P&H board v1.1b INJ4 constantly switched on

Postby jsdevel » Fri Dec 02, 2016 7:07 pm

After assembling my board and wiring it up to my MS2 card, INJ4 was constantly on. I verified that the jumper wires each had 12 Volts. Any help would be appreciated. Cranking my cam/tach input lit up the LEDS on INJ1-3.
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Re: P&H board v1.1b INJ4 constantly switched on

Postby jbelanger » Fri Dec 02, 2016 7:27 pm

Check the resistance between the metal tab on Q5 and ground. It should be very high or even infinite. If not, your problem is likely related to either a badly installed isolator or mounting hardware or you need to clean up the mounting hole to make sure there is no metal swarf.

If that checks out, check the voltage on pin 1 of Q5.

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Re: P&H board v1.1b INJ4 constantly switched on

Postby jsdevel » Fri Dec 02, 2016 7:50 pm

OK. Mounting tab of Q5 to 5v ground showed an OHM value of ~ 186 on my multimeter. The rest all showed greater than 2.5 K OHM. I'll re-mount Q5 to the case and ensure there are no burs touching the screw.
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Re: P&H board v1.1b INJ4 constantly switched on

Postby jsdevel » Fri Dec 02, 2016 8:48 pm

OK. Remounted Q5 and now I show around 200 mV from 5v to INJ4. Is that normal? Could that be stored capacitance or did I fry the MOSFET?
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Re: P&H board v1.1b INJ4 constantly switched on

Postby jbelanger » Fri Dec 02, 2016 9:16 pm

You should have a lot more than 2.5k Ohm. Are you sure all the diodes are the correct way in? And where are you measuring the 200mV?

It is possible to get a failure from the TIP122. To check that it's still not a mounting/isolation issue, you can remove the mounting hardware and lift the metal tab away from the heat sink and check if it behaves as it should. Don't drive the injector that way or do it for a very short time because you will get significant heat quite fast.

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Re: P&H board v1.1b INJ4 constantly switched on

Postby jsdevel » Thu Sep 21, 2017 9:52 pm

Turns out I did have a few heat sinks touching the case. Isolating them properly cleaned this up!
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