MS2 V3 blowing fuse on car

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MS2 V3 blowing fuse on car

Postby metalinvalidmatt » Thu Dec 14, 2017 7:57 am

back again - finally got a reason to put my MS2 in something, initially had an issue with the 5v reg in it (blown from ??? some time ago - diode had failed by fusing itself together.. anyway)

here's my issue, I have a megastim and a shitty PSU powering it when I was initially setting up the MS for a sorta base tune/something to start with.
worked fine, had a 5a fuse on it anyway but also worked fine on a 3a fuse. multimeter tells me it draws about 0.8amps just doing "nothing" (it's setup for an FC style ignition, went by aaroncake's info, zeal board and boost mod added)
now that seems a bit high, but either way it appears to be working fine

upon wiring it into my FC, key on and the fuse pops.. check some other things, disconnect a couple things.. fuses popping left right and center, 3a fuse to be precise. (the one powering the MS2)
after legit cutting ties with everything apart from POWER AND GROUND, the bastard still only wants to pop fuses all day long. yet, works on the bench.

something has GOT to be wrong here, but I would like some sort of pointer of where to begin looking, the fact it runs on the bench but not on the car, well really the car battery should I say.. which is a hair under 12v, other thing I guess I could mention is the PSU I've used to get it working on the bench is again, kinda craptacular and has variable output, 0-15v or so, seems to max out around 8ish with the megasquirt, so must not have much power behind it if you know what I mean

anywho, any help would be helpful.
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Re: MS2 V3 blowing fuse on car

Postby DaveEFI » Thu Dec 14, 2017 8:13 am

You have your answer. You bench power supply can't do enough current to pop the fuse - so it's dropping its voltage instead.

You have a short etc somewhere inside MS. Start by disconnecting all the bits you've added, and note the voltage on your PS after each. Pretty well any is big enough to drive just an MS and Stim.
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Re: MS2 V3 blowing fuse on car

Postby metalinvalidmatt » Thu Dec 14, 2017 8:28 am

thanks, I guess I'll keep going through the diodes and what not - it was significantly more noticeable with the diode I replaced before, that was basically bottoming out the PSU (and it had blown some tracks when it first went)

the MS2 would also disconnect (soft-powerdown?) after a few minutes when bench testing which also points to something drawing too much power/grounding out mildly I suppose, might have to try to see what warms up to get an idea whereabouts it may be.. urgh this thing is a headache especially when I don't know why/how it went to begin with
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Re: MS2 V3 blowing fuse on car

Postby DaveEFI » Thu Dec 14, 2017 11:10 am

Did you build this unit yourself - or was it ready made?
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Re: MS2 V3 blowing fuse on car

Postby metalinvalidmatt » Mon Jan 01, 2018 1:29 am

back again, thought i'd have another look at this thing.

board was DIY.

did a little more probing and it *seems* like Q5 and probably Q1 seem to be heating up a bit more than the rest of the FETs, I double checked all the diode directions and they're fine

I read that Q12 and Q9 should have around 60K of resistance to ground on the tab - however mine only have 2.5K (though not 0 so damaged component, not accidentally grounded?)
beyond that I also notice with the stim plugged in that referencing the ground on the stim as ground, then probing voltage on the heatsink results in a 200mv measurement.. but I'm guessing that's probably related to the last line..

any ideas/things to check? I'm assuming I should replace Q12/Q9 but maybe others too? this is rather frustrating :(
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Re: MS2 V3 blowing fuse on car

Postby metalinvalidmatt » Thu Jan 04, 2018 7:14 am

little update, seems Q9/12 have the 60K of resistance when the board is disconnected (from a stim) but 2.5K when connected (to a stim) is that right?

yet another update - lucky I didn't post ^ that just yet, I just de-soldered the middle pin from Q9 and removed Q12 (due to a bend in the leg I couldn't get it to just sit in the through-hole gap without being connected) and I see now the system isn't drooping voltage like it was, so there must be faulty parts/traces/etc going on here.. hopefully I'll get to the bottom of it soon as I really want this to work :( (then I've got to get my engine rebuilt.. then get the raspberry connected/mounted.. urgh so many things so little time :P )
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Re: MS2 V3 blowing fuse on car

Postby DaveEFI » Fri Jan 05, 2018 2:45 am

You can't really measure resistance on a component which is powered up. As the DVM supplies its own power to measure resistance.

Q9 and Q12 must be insulated from the heatsink. You won't get an infinity reading on an assembled board, but a short will read only a few ohms
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Re: MS2 V3 blowing fuse on car

Postby metalinvalidmatt » Sat Jan 06, 2018 8:40 pm

DaveEFI wrote:You can't really measure resistance on a component which is powered up. As the DVM supplies its own power to measure resistance.

Q9 and Q12 must be insulated from the heatsink. You won't get an infinity reading on an assembled board, but a short will read only a few ohms

I understand that - I meant the stim was connected, not powered.. I probably should have mentioned that.

Is it a dumb Idea to remove Q9/Q12 and attempt some tests (see if I can get the thing to start up/idle) or no? it mentions they're part of the overcurrent protection or some such, so I assume I just wouldn't have the protection, correct?
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Re: MS2 V3 blowing fuse on car

Postby DaveEFI » Sun Jan 07, 2018 2:59 am

Personally, I'd fix all faults on your MS on the bench before ever putting it near the car.
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Re: MS2 V3 blowing fuse on car

Postby metalinvalidmatt » Sat Jan 13, 2018 7:23 pm

I ordered and replaced all the transistors in the injector protection circuits to no avail, problem is still there, diodes and resistors look to be fine, possibly some internal wiring issue?

so I figured I would remove the secondary pwm protection (eg the part that uses Q12/Q9) to see if that would help the current issue. it kind of does, however Q11 gets super hot within 30seconds + of being plugged into a car, something is still stuffed..
probing through the circuit I really can't see how or why this thing will not work as it should
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Re: MS2 V3 blowing fuse on car

Postby DaveEFI » Sun Jan 14, 2018 2:26 am

Inj 1&2 use identical circuits. Measure voltages etc on the good one to see where the fault is on the bad one.
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Re: MS2 V3 blowing fuse on car

Postby metalinvalidmatt » Sun Jan 14, 2018 5:26 am

DaveEFI wrote:Inj 1&2 use identical circuits. Measure voltages etc on the good one to see where the fault is on the bad one.

not too long after my last post I had done this and noticed a slight difference in working voltage between the two sides, very little but I figured it was a sign - looking at the circuit I really couldn't see how bad it could be unless there was some unknown semi-short somewhere, what I ended up trying was taking D20 and R33 off the board, then lifted leg 1 of Q11 and soldering the components DIRECTLY onto Q11 as they should be connected as per the circuit.. somehow the thing stopped heating up like it was, and I actually managed to get the car to half-start, just having a few pops and splutters surprised me after I got the components under control, then it managed to 'start' (haha if you could call it that) on 1 rotor (13b turbo S4) while the otherside was flooded to hell, I think for the most part that's a tuning issue, and that's probably the side with the apex seal semi-failure, so it had trouble starting on the previous EMS anyway. (am just trying to confirm the MS2 works on my setup before taking the engine out and getting it re-done, I didn't want to be playing these games on a brand new motor..)
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Re: MS2 V3 blowing fuse on car

Postby DaveEFI » Sun Jan 14, 2018 6:08 am

If you have a fault on an injector driver, it might be switching those injectors on at all times. Hence not even attempting to fit MS to the car until you are certain it is working perfectly.

If you're having problems fixing it, might be worth ending it to someone more used to fault finding them?
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Re: MS2 V3 blowing fuse on car

Postby hybrid » Tue Jan 16, 2018 10:09 pm

Do you have a Stim?
You should be able to see what the injector drivers are doing (in a simple way) via the LEDs on a stim.
Do not load someone elses tune and expect it to work for you!
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