MS II troubleshooting

[zegarsm]

hello this will be long so bear with me. So I got my megasquirt 2 last summer for my 92 eagle talon turbo awd. I assembled the board and got it got work with the stim fine, rpm and all the knobs on the stim worked as they should on tunerstudio. I had the board set up to work with the stock cam angle sensor with the dual inputs. When I got to wiring it up the my car is when everything went wrong. I think I shorted the cars 5v sensor signal to the ms through either the tps or one of the cam angle sensor inputs I really cant remember because it happened so long ago but I know for sure something go shorted. I suspect that I fried the processor but I am really not sure. Now none of the lights on the ms come on when I power it up. I've been at college the for the last 9 months and had no time to peter around with it and see whats wrong and now that I'm on summer break I wanna final get this this running. Is there any easy way to see if the ms II processor is functional or not, I cannot get the ms to connect to tunerstudio anymore so I am guessing the processor is fried. I know this is a pretty vague post but any advise would be helpful. If you need any more information about my setup please ask.

Thanks,
Mike

[Matt Cramer]

Is the problem with not connecting to TunerStudio something that only happens on the car, or can you duplicate it on the Stim?

If it happens on the Stim, what happens if you try to load firmware?

[trakkies]

Before guessing the worst, go through the Serial Communications Construction & Testing section in the assembly guide. Comms - especially using a USB to serial converter - seem to account for lots of problems.

[zegarsm]

Ok, I guess it would be a good idea if I went thought all the troubleshooting on the assemble guide so Ill go though all of that and post back. Also the ms is completely non responsive even when hooked to the stim when you power it up no lights flash. I checked the stim and turns out the processor on the stim is in fact dead, the voltage regulator get really hot when the processor is plugged in and is fine with the processor out. Even with processor out of the stim shouldn't it still be able to at least power up the ms?

[zegarsm]

I went through the power supply troubleshooting from the megamanual and I checked all the proper pins on the processor socket for 5V and none of them were satisfactory. I also checked the voltage regulator and from ground to the left pin it had around 6 volts and I have a 12 volt power supply currently hooked to the MS so that is a problem. From ground to the right pin of the voltage regulator I get around 0.1 V and it should be 5V. Where should I go from here?

Thanks

[trakkies]

My first check would be C17 - the main smoothing cap for the 5 volt supply. These tantalum caps can go short circuit. But is your 12v supply still giving 12v if you're only seeing 6 volts at the reg input?

[zegarsm]

Ok so I checked the voltage of the powersupply while the MS is powered up and it was 7 V (the power supply is 12V) and it kept dropping the longer it is plugged into the MS. I checked the resistance of C 17 and it was only 1.6 ohms.

[zegarsm]

What should the resistance between pins 15 and 16 on U6 be? I'm getting 1600 ohms and since those are the pins for VCC and ground shouldn't it be much higher?

[zegarsm]

Scratch that, that was with U6 still in the board. With it out pins 15 and 16 on the chip read 6 Megaohms but the pins on the board still read 1600 ohms.

[Matt Cramer]

1600 ohms from 5 volts to ground isn't all that surprising.

[zegarsm]

Yea after looking over the schematics that looks about right because there is 2 1000K resistors that go from VCC to ground in the VR section of the board. This may be a dumb question but what exactly is VCC, from looking at the schematics it looks like its just a 5V supply for all the components of the board. C 17 was the first one I removed and the pins on the board read only 1.6 ohms, after removing more components the resistance kept going up untill it reached 1930 ohms then it just stays there which seems correct because of the 2 1000K resistors in the VR section. I probably should have been keeping track of exactly what component had the greatest effect on the resistance from VCC to ground but I think I think I got rid of the short. Should I replace all the removed components with new ones and proceed from there.

[Matt Cramer]

Right, VCC is the main 5 volt supply connection.

[trakkies]

Ok so I checked the voltage of the powersupply while the MS is powered up and it was 7 V (the power supply is 12V) and it kept dropping the longer it is plugged into the MS. I checked the resistance of C 17 and it was only 1.6 ohms.

How are you measuring C17? With a DVM set to resistance, it should give a varying value as it charges, ending up at a high reading. If it is staying at 1.6 ohms it is toast so replace it. It is shorting out the 5 volt rail.
If you are measuring with an ESR meter, 1.6 ohms would be ok. But you are looking for something which is shorting out or heavily loading the 5 volts rail.

[zegarsm]

I should rephrase that, C17 was removed and the pads of C17 gave 1.6ish ohms. The capacitor itself had 5 megaohms and just creeped up. Yes, I am using a regular volt meter set to resistance.

[Bernard Fife]

z,

Personally, if this is a V3 board I would check D19 first. It shunts excessive voltage on the 5V side to ground, so is likely to burn up if exposed to 12V. There is more on this here: http://www.megamanual.com/ms2/V3trouble.htm especially step 14. You can pull up one end of D19 and check again. If that doesn't help, there are more hints in the link.

Lance.