MS3 board Vcc short

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MS3 board Vcc short

Postby Kzcleve » Tue May 29, 2012 11:25 am

I have a question about MS3 board (Daughter card) repair. I have an MS3 with a V3.0 main board and the MS3X expansion that I purchased in February. It went together well and I got the car up and running fairly easily. I was very impressed with the products. However, about a week ago I ran into a problem. I had driven the car to work and it ran perfectly. When I started the car after work, it idled pretty rough so I connected my laptop to to use tuner studio to see what was happening. I saw that there was some sync loss and some of the sensor reference voltages were incorrect (no data log). I immediately started to look through my wiring harness for any shorts or problems. I found none and I had to get the car home so I drove about one mile and decided that I needed to pull off of the road and make a better inspection of the wiring. I turned the car off and inspected the wires again (both visually and with a digital volt meter). I did not find any problem with the wiring harness so got back in the car and tried to take another look in tuner studio but the MS3 would no longer communicate with tuner studio or power on. When I installed the MS3, I left my factory wiring and ECM in the car for just such an event, so I was able to switch back over to the factory ECM and drive home with the MS3 disconnected.

Since then I have inspected the V3.0 main board, the MS3 daughter board and the MS3X board. I found that polyfuse 1 F1 was tripping and that the 5 volt regulator was damaged, so I replaced both but the polyfuse continued to trip. upon inspection of the MS3 Daughter board I found that the VCC circuit on the MS3 daughter board has a short somewhere. There is only 1.2 ohms resistance at any point between Vcc and ground on the MS3 daughter card with the daughter card removed from the main board. And with the daughter card removed from the main board, the main board ohms correctly everywhere. However, if i return the daughter board to the main board, all vcc points on the daughter card and the main board have only 1.2 ohms resistance between Vcc and ground. And if 5 volts is applied directly to the vcc pin on the 40 pin connector for even a second (whether in or removed from the main board), the processor starts to heat. I am worried that the processor itself has the short. I inspected all pins of the processor using a 100x-300x microscope to see if there was any solder bridge or similar short but I was unable to find any problem and no components are visually damaged. I am certain that the short is on the MS3 daughter board but without a correct schematic for the board it is more than difficult to make an accurate diagnosis of the specific component that has shorted to ground. I do have experience soldering and testing SMD components but I would still be limited to testing only the capacitors, resistors, and diodes.

My setup at the time of the problem was MS3 with MS3X card and v3.0 main board running Beta 19 firmware. Full sequential fuel on a V8. Fuel only at the time of the problem however it was set up for COP with GM optispark being used for crank/cam signal. I am not using the IAC output but the main board is wired for a 4 wire IAC. I have been running the car on the MS3 for about 2 months and I had not made any hardware changes in more than 6 weeks before the problem. Sorry this was a long post. I have contacted DIYAutoTune.com and let them know. I am waiting to hear back from them. What I am looking for here is possible causes, any ideas on the specific component of the MS3 daughter board that might be the culprit, and hopefully any help I get can help others. There is no MSQ and datalog because I am fairly certain that they won't do much to help. Thanks
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Re: MS3 board Vcc short

Postby racingmini_mtl » Tue May 29, 2012 11:34 am

If the processor heats up when you apply voltage, it is almost certain that it has failed and needs replacing. There are a few people here who can replace them.

Jean
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Re: MS3 board Vcc short

Postby Kzcleve » Tue May 29, 2012 12:08 pm

Thank you for the post. That was my suspicion and I will work out just what to do about repairing the processor. I am still curious as to the cause for the processor failing. I am having a hard time diagnosing what could have caused the processor to short. I know that if 12v hits the 5v plane that will cook the processor but I really don't see how that would have happened in my case. I just don't see what else could have caused that issue. Any other short should have been dealt with using the main fuse or one of the polyfuses or at a last resort the on chip voltage regulator. I am reluctant to put a new processor in a system that could just damage it again.
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Re: MS3 board Vcc short

Postby Peter Florance » Tue May 29, 2012 5:06 pm

racingmini_mtl wrote:If the processor heats up when you apply voltage, it is almost certain that it has failed and needs replacing. There are a few people here who can replace them.

Jean

Recently I've seen a couple that get the regulator hot but don't heat themselves. Not sure how that failure mode is different other than they don't have the little hole in them either.
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Re: MS3 board Vcc short

Postby racingmini_mtl » Tue May 29, 2012 6:32 pm

Peter Florance wrote:
racingmini_mtl wrote:If the processor heats up when you apply voltage, it is almost certain that it has failed and needs replacing. There are a few people here who can replace them.

Jean

Recently I've seen a couple that get the regulator hot but don't heat themselves. Not sure how that failure mode is different other than they don't have the little hole in them either.

You mean they draw a lot of current but they don't get hot? That's interesting.

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Re: MS3 board Vcc short

Postby Peter Florance » Tue May 29, 2012 6:46 pm

racingmini_mtl wrote:
Peter Florance wrote:
racingmini_mtl wrote:If the processor heats up when you apply voltage, it is almost certain that it has failed and needs replacing. There are a few people here who can replace them.

Jean

Recently I've seen a couple that get the regulator hot but don't heat themselves. Not sure how that failure mode is different other than they don't have the little hole in them either.

You mean they draw a lot of current but they don't get hot? That's interesting.

Jean


Yes because the voltage drop is in mv

The regulator is where the drop happens.
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Re: MS3 board Vcc short

Postby racingmini_mtl » Tue May 29, 2012 6:55 pm

Peter Florance wrote:Yes because the voltage drop is in mv

The regulator is where the drop happens.

I understand that. But that means they fail as a quite solid short because even a small resistance would mean a significant power would be dissipated with the ~1A+ that the voltage regulator will supply.

As you said, a different failure mode.

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Re: MS3 board Vcc short

Postby Peter Florance » Tue May 29, 2012 6:58 pm

racingmini_mtl wrote:
Peter Florance wrote:Yes because the voltage drop is in mv

The regulator is where the drop happens.

I understand that. But that means they fail as a quite solid short because even a small resistance would mean a significant power would be dissipated with the ~1A+ that the voltage regulator will supply.

As you said, a different failure mode.

Jean


I think the part # of the regulators have changed from the LM2937 and they may limit differently. I don't think I'm seeing 1 amp or even close to that.
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Re: MS3 board Vcc short

Postby Kzcleve » Wed May 30, 2012 11:42 am

Thank you for the insight. I do have another question though. Have any of you seen capacitors on the MS3 card short to ground?
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Re: MS3 board Vcc short

Postby Peter Florance » Wed May 30, 2012 11:50 am

Kzcleve wrote:Thank you for the insight. I do have another question though. Have any of you seen capacitors on the MS3 card short to ground?

No, but it can look shorted if the CPU is shorted.
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Re: MS3 board Vcc short

Postby Kzcleve » Wed May 30, 2012 2:37 pm

Perfect, then I will just focus on the CPU replacement and double checking wiring and soldering as causes for the failure. Thank you for all of your help. I will add updates if I find anything worth sharing.
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Re: MS3 board Vcc short

Postby jsmcortina » Wed May 30, 2012 2:51 pm

Do remember that a replaced CPU needs the "monitor" code reloading. That can only be done by a few Megasquirt agents.

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Re: MS3 board Vcc short

Postby Kzcleve » Tue Jun 19, 2012 8:28 am

Just as an update for anyone looking for something similar, it looks like the wideband was the cause. It looks like it might have been possible for the 12v wire at the wideband gauge to contact the 5v (the wire that goes to the MS3) at the gauge. I am fairly certain that 12v ended up on the 5v and pop goes the CPU. Thanks for the help and advice.
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