MS2 Power Up and Smoke

[Nicholas H]

Well I finished up my MS2 and triple checked everything looked good to go. This is my first megasquirt but I was rather confident in my solders as this is not the first PCB I have put together. I did not place the microprocessor on the board but rather wanted to check the board voltage after 12v was supplied. Checking the 0v, 5v, and 12v pins going to the daughter board. I do not have a stimulator...yet though I can imagine I am going to need one now. long story short I placed a 5amp fuse off of the battery connected pin 19 ground and the pin for 12v, heard the current draw looked over and a small puff of smoke arose from the board and I removed the contact immediately. The location I believe to be around the R52 POT. Using my nose it somewhat smells like it but it is not very strong so I may be wrong. I applied voltage again to try to pinpoint the culprit but there was nothing else. Nothing got hot, made noise, or expelled more smoke. While connected to power the second time I tested the pins going to the daughterboard all checked as they should. 5V on pins 1, 20, and 31 with 12v on pin 16. I have measure the POTs using a fluke 77 and R52 appears to be operational yet with 98 K ohms max and decreases with adjusting the top screw. The lower R56 does not appear functional and is stuck at 551 ohms. I fear this may be the problem, and any circuit it may have effected. possibly U7 that is in the same area as R52 smoked?

This is a MS2 running VR trigger input, stepper idle control, logic spark outputs

Attached are pictures of the setup. Bottom picture was from yesterday but remains the same except I removed the jumper from js10 to ign.
Any advice on things to test with a DMM would be appreciated. This has made me sick to my stomach a little.

rsz_p1010405.jpg

rsz_p1010406.jpg

As always your help is appreciated.
-Nicholas H

[Hey_Allen]

I am not an expert on what all may cause issues on the MS3 PCB, but just looking at the pictures gave me a few questions.

The reverse side of the board looks like there may be some solder bridging between pins, or nearly bridging, up on a couple of the high power transistor solder pads, such as Q5.

Looking at the front side in the same area, I can't tell if the mica or silicone insulators are under the heat sink mounted devices that require them, which would cause issues if they are shorting to ground through the heat sink.

[Nicholas H]

Thank you for the concern with the bridging. I have checked several times for bridging of the joints on the small 3 pin joints but have made sure to solder suck all joints when making and checking resistance between the solders such as on Q22, Q23, Q13, Q14, Q15, ect. I will try to get a better picture with better lighting tomorrow so any possible mistakes that were made. Concerning the mica insulators, only Q9 an Q12 called for mica insulators which were not used in my application. Q3 and Q11 I did wonder if I should use the supplied thermal tape but a search of placing these directly on the heat-sink using thermal grease returned this: http://www.msextra.com/forums/viewtopic ... 32&t=43422 so I only used thermal paste on these. Q3 and Q11 do have metal tabs so maybe the forum thread was incorrect in suggesting mica was not needed. One question I wondered was does this thermal grease carry electrical current if it were to bridge any contacts? It is the grease labeled NTE303 that is included in the MS2 kits. Curiosity more than anything. Again I will try to get better pictures tomorrow.

thank for your time,
Nicholas H

[Nicholas H]

The component in spot Q9 is for boost control and is the IRLZ44ZPBF-ND with mica insulator below. All other components have been places on the heat-sink using the thermal paste.

To clarify jumper wires:
Stepper idle control circuit is wired as manual suggests. JS0-3 jumped to IAC1A, IAC1B, IAC2A, IAC2B
VR sensor circuit is used so TACHSELECT to VRIN
MapDaddy upgrade so upper left most point on MAP sensor board is jumpered to JS5
S12C jumpered to JS9(+12C)
TSEL jumpered to VROUT
Logic level ignition is to be used to power coil on plug wasted spark for a 4 cylinder using the manuals suggested wiring with the TC4427AEPA and 15 OHM resistors. Spark A goes to SPR1 and Spark B goes to SPR2

I can attach power to this board without any further damage occurring if there are a few tests and voltages that can help diagnose where my damage component lies. Even sending the board in for testing would not be out of the question at this point.

Let me know any of your ideas that may help diagnose where the problem and damaged components lie. It happened so fast but I believed to have seen the smoke come from the R52 area near the U7.

Thank you,
Nicholas H

[slow_hemi6]

Whats all over the crystal?

[dontz125]

Looking at the V3.0 schematic, the only way I can see blowing R56 is to have something across pins 2 & 3 (middle and lower) while the pot is wound all the way out; this would give a dead short from 1 (Vcc) through 2 (wiper) to 3 (ground). Last night I had to carefully brush out a tiny bit of wire strand that had gotten between two pins of an IC. Fortunately, I discovered it using an ohmmeter ("Why are these pins shorted?!") and not by heating various components to incandescence (I've used that method too, on occasion ).

There is nothing obvious in the pic, but the solder on those two pins does look a little odd. If this is what's happened, then whatever caused the short may have burned up or simply fallen away when you picked the board up to investigate.

[Nicholas H]

Good morning everyone,
The crystal is laying in some RTV for vibration suppression. I didn't think of a piece of wire falling under the R56 and shorting the terminals. I will have to take a closer look and see if there is evidence that something may have burned away under either R52 or R56. Your reply instills hope that I may have not totally fried something. If there was something wrong with the VR circuit would there be any way to test other than a stim board? Is there somewhere to send MS2 to have someone look over everything before I plug the daughterboard in? With how many megasquirts are out there I'm surprised there isn't almost a stim board rental.

Thank you so much for taking a look,
Nicholas H

[elutionsdesign]

I do repair work, you can PM me for a shipping address.

[slow_hemi6]

Good morning everyone,
The crystal is laying in some RTV for vibration suppression. I didn't think of a piece of wire falling under the R56 and shorting the terminals. I will have to take a closer look and see if there is evidence that something may have burned away under either R52 or R56. Your reply instills hope that I may have not totally fried something. If there was something wrong with the VR circuit would there be any way to test other than a stim board? Is there somewhere to send MS2 to have someone look over everything before I plug the daughterboard in? With how many megasquirts are out there I'm surprised there isn't almost a stim board rental.

Thank you so much for taking a look,
Nicholas H

RTV silicone is acetic cure. That makes it conductive.

[Nicholas H]

Most interesting. I will definitely remove it and see if maybe if the crystal has burned up. That would have been in about the same area as where I saw the smoke. Are there any definitive signs that would indicate a burned crystal? And also if it had shorted at the crystal terminals, what sort of damage may have been caused later in the circuit?

Thanks,
Nicholas H

[Hey_Allen]

Once you have traced down and fixed any damage, look for electronics safe Silicone RTV. Different cure chemistry that does not turn acidic or conductive, though it does go from opaque white to a faintly yellow color over time.

[Nicholas H]

I sure will. I plan to use a small amount of 100% silicone. I am planning on sending this MS2 out for diagnosis and repair in the next couple days if there are no break throughs by then. I figure it might be a good idea to have someone with a stim board to double check everything is ready to go. I am still looking for testing methods to check the crystal and its relating circuit if anyone has ideas I would be all ears.

thanks,
Nicholas H

[racingmini_mtl]

The crystal and its relating circuit are not used with MS2. You can simply ignore it. But it would be a good idea to remove the RTV silicone and clean the board.

Jean

[Nicholas H]

Could the crystal have been shorted due to RTV and caused the smoke I saw or is it a rather long shot. I was just curious if I should continue to think about sending the board out for diagnosis and repair or if I should risk it and plug the CPU in and power it up. I would hate to send it out only to find that nothing was wrong but at the same time I would hate for there to be something still shorted and fry my CPU costing more money.

Thanks,
Nicholas H