Trouble finding bad component *SOLVED*

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DHH
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Trouble finding bad component *SOLVED*

Post by DHH »

I was confident I wasn't going to have problems with the assembly of my MS3x, but the baseball bat of reality hit....and here I am.

I'm assembling the MS3 V3.0 and seem to have a faulty component in my injector or power circuit that I just can not find.
I'm hoping someone can help point me in a the right direction, as I keep replacing components without a solution.

I apologize for the long explanation:

When I powered up the board for the first test as per section 13.5 "Testing Stage", I had a bit smoke come from around the U4/D18 area. Couldn't tell exactly where. Powered it down and I'm embarrassed to say, that I found the board was sitting on a couple strands of bare wire.

I removed the wire and powered it back up to see if the fried component had any smoke left in it; in order to pinpoint which item blew. No smoke and everything felt cool to the touch, so I proceeded with the voltage test and had 4.99v on U1 Pin 1,20,31 and 11.4v on pin 16. (Power supply voltage is 12.18v).
I then noticed that Q11 was very hot to the touch, so I powered down.

I tested every component on the board and couldn't find anything obvious.
So this is where I am at right now:
Every resistor is ok. (I did find that I was supplied a 47k for R13, instead of 4.7k but that would not have any influence on my issue)
Initially I was convinced it was the injector (2) circuit that was the problem, so I have replaced - Q11,12,13,15 and D7,18,20
After replacing all these components (and with U4 removed), I powered it up and C14 smoked.
I removed C14, and without the cap in place, I powered it back up and the +ve hole for C14 gets hot. It melted some solder paste that was on it. Nothing else connected on that trace is showing signs of heat.

I found a post by James suggesting to test the following points to help pinpoint a possible short.
It said to look for 12v at: S12, S12C, center leg of Q9 and Q12, D3 anode, left leg of U5, D9 cathode
and 5v at: S5, the two +5v proto holes, D9 anode, right leg of U5, D19 cathode, CPU pins 1,20,31.

I had the following voltages:
S12 - 12.05v, S12C - 11.42v, Q9 & Q12(center) - 12.14v, D3 anode - 12.09v, U5(left) - 11.37v, D9 cathode - 11.37v.
S5, Proto 5v, D9 anode, U5(right), D19 cathode, CPU 1,20,31: All were 4.99v
So everything tested ok there.

I also tested the voltages at each pin of U4 (U4 is removed) and got the following:
1 - 1.35v, 2 - 5.03v, 3 - 0v, 4 - 5.96v, 5 - 0.06v, 6 - 11.58v, 7 - 0.04v, 8 - 0.6v
Can't figure out how pin 2 and especially pin 4 could have a higher voltage than the 4.99v output of the regulator circuit. Also don't know why anything shows on pin 1 & 8, as the schematics show these are not connected to anything.

Any help would be greatly appreciated as I have 3 full days into searching and troubleshooting and don't seem to be getting anywhere. Attached pdf shows replaced components, currently removed components, and U4 pin voltages
Thanks in advance for any help.

EDIT: The smart thing for me to do would be delete this post to avoid the embarrassment of what the problem was.......but if I was smart, I wouldn't have had to make this thread in the first place.
So......I am leaving this thread up in case it helps another newb in the future. The entire problem seems to be from the type of flux I was using. I have both a plumbers flux and electronics flux (both are lead free), but I never really paid attention to which one I was using.

The voltages I was getting on pins 1,2,4 and 8 made zero sense to me. They were the equivalent of jumping out a window and falling up. Not possible, unless I had stumbled upon the secret of creating energy. The only way I could figure that those voltages could be true is if the pcb was shorting internally (not likely) or on the surface. So I scrubbed the board down with alcohol and let it dry over night. Plugged it in this morning, and voila, problem solved. I still get a minor trace voltage on pin 8, but all the other voltages are what they should be, and cap 14 is no longer heating up.
I'll give it another scrub to try and completely eliminate the pin 8 voltage and I need to reinstall C14 and Q9,12 for a full test, but looks as if problem is solved.
6.2L LS3, Procharged, MS3X V3.0
22' Donzi Classic
Not yet running...
http://www.donzi.net/forums/showthread. ... 502-to-LS3 (Disclaimer: Contains naive info :D )
billr
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Location: Walnut Creek, Calif. USA

Re: Trouble finding bad component *SOLVED*

Post by billr »

Yes, those voltage readings didn't make sense to me either. I could only guess that a short on/in the PCB had been created during your smoke episode. I was waiting for somebody else, who might know better, to jump in before asking you to post pictures of the board so we could try doing a visual inspection. I was holding off on that (pix) because not much would show with a short internal to the PCB, and that was what I was afraid was the problem.
DaveEFI
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Re: Trouble finding bad component *SOLVED*

Post by DaveEFI »

My rule of thumb is to avoid lead free solder for home construction. And use a 60/40 leaded multi-core solder than contains the flux. You may not find that in a corner store, but will at a proper electronics supplier.
Rover SD1 3.5 EFI
MS2 V3
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billr
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Joined: Sun May 15, 2011 11:41 am
Location: Walnut Creek, Calif. USA

Re: Trouble finding bad component *SOLVED*

Post by billr »

Indeed, common lead-free solders usually have a considerably higher melting temperature from 60/40; you don't want to apply any more heat than necessary to the PCB or components to be installed. And, can you even find the small-diameter (.015"-.031") solder needed for electronics work anywhere other than an electronics supplier?
DHH
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Re: Trouble finding bad component *SOLVED*

Post by DHH »

billr wrote:Yes, those voltage readings didn't make sense to me either. I could only guess that a short on/in the PCB had been created during your smoke episode. I was waiting for somebody else, who might know better, to jump in before asking you to post pictures of the board so we could try doing a visual inspection. I was holding off on that (pix) because not much would show with a short internal to the PCB, and that was what I was afraid was the problem.
A short in the PCB was my fear, but I also knew that was extremely unlikely. I actually don't think the bare wire the board was sitting on caused any component to smoke. In fact, no component appeared to have any damage and they all tested ok. The smoke I saw was the flux burning off (around C14). Even C14 survived, despite it's +ve hole getting hot enough to burn the flux (although I replaced it anyways).

It looks as if I'm ok to move ahead now, as I had it powered up for close to 30min yesterday and nothing warmed even the slightest and all voltages where as they should be. Wasted three full days chasing the "fault". At least I learnt something I won't forget. :D
6.2L LS3, Procharged, MS3X V3.0
22' Donzi Classic
Not yet running...
http://www.donzi.net/forums/showthread. ... 502-to-LS3 (Disclaimer: Contains naive info :D )
DaveEFI
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Posts: 4175
Joined: Sun Apr 15, 2012 12:55 am
Location: SW London, UK

Re: Trouble finding bad component *SOLVED*

Post by DaveEFI »

I've never know proper electronic flux to be conductive - except perhaps in a very high impedance/high frequency circuit not found anywhere on MS. But flux residue can hold bits of solder or some other form of conductive particles could stick to it. Something a magnifying glass and powerful light will show.
Rover SD1 3.5 EFI
MS2 V3
EDIS
Tech Edge O2
London UK.
billr
Super MS/Extra'er
Posts: 6828
Joined: Sun May 15, 2011 11:41 am
Location: Walnut Creek, Calif. USA

Re: Trouble finding bad component *SOLVED*

Post by billr »

OP said some "plumbers flux" may have been involved. That stuff is often water-based and aggressively corrosive, lots of chances for getting conduction through it.
DaveEFI
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Posts: 4175
Joined: Sun Apr 15, 2012 12:55 am
Location: SW London, UK

Re: Trouble finding bad component *SOLVED*

Post by DaveEFI »

Perhaps we need a new word for electronics soldering to differentiate it from other types. :D
Rover SD1 3.5 EFI
MS2 V3
EDIS
Tech Edge O2
London UK.
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