Injector output fault.

[trakkies]

Have an MS1 V3 which is presenting a (near) dead short to the supply. Lifting the +12v to one TIP 125 removes the short.
Is there an order of the most likely component(s) to fail I should follow?

[Matt Cramer]

It sounds like the TIP125 isn't properly insulated from the heat sink.

[trakkies]

It sounds like the TIP125 isn't properly insulated from the heat sink.

No - that's fine. It was working ok at one point. Something in one injector driver makes it effectively a short circuit when powered up - the other is fine. I was just hoping to cut down on checking time by asking if there was a likely component failure.

[trakkies]

Turned out to be the FET. Robbed a new kit I'm building of one.

Which brings me on to another question. The manual says it is a IRFIZ34N. The one in the recent kit a FDPF3860T. Are they direct equivalents as the latter isn't easy to source in the UK. And postage from Digikey is horrendous. But if it is an improvement, I'll pay the extra.

[Matt Cramer]

Not sure where you got your setup, but several of the kit makers will substitute equivalent parts from time to time.

[trakkies]

Not sure where you got your setup, but several of the kit makers will substitute equivalent parts from time to time.

The one I robbed came from DIYAutoTune. I realise there may be substitutions - but in the case of the ignition driver the later one is said to be better then the one given in the original circuit? If the injector output transistors are just an alternative, I'll source the originals from the UK and not pay the silly postage rates from DigiKey.What p***es me off is DigiKey have a UK website - but insist on using high price carriers even for low value items.

If the US is serious about trying to regain its former position as an exporter of goods, it needs to do something about its postal/carriage services. I can get goods from China for far less cost. And in the UK I can just pop such things in the letter post and be certain it will get to its destination.

Rant over.

[Matt Cramer]

Yes, the injector drive transistors were just a straight up substitute.

[trakkies]

Yes, the injector drive transistors were just a straight up substitute.

Thanks, Matt.