Testing MS & all lights go dim / out

nebraska_e28 · Post by **nebraska_e28** » Wed Jun 16, 2010 10:54 am

MS II v3(code 2.86)

I just finished finally assembly of MS. When I power it up via Jstim, both injector lights on the stim alternate & D14 flashes with them. Adjusting the CLT pot makes D15 go on & out. After maybe 15 seconds everything goes out & I can see the power light on the stim go dim. All tests prior to this final one checked out ok.

First thing I checked for were solder bridges & didnt see anything. Does this sound like a short or something that I'm missing?

Thanks for the help!

nebraska_e28

Matt Cramer · Post by **Matt Cramer** » Wed Jun 16, 2010 11:25 am

Sounds like a short, all right. To check for a short in the Megasquirt PCB, power up the Megasquirt on a Stimulator or on the car and check the following points for voltage with a multimeter.

You should find the same voltage as the battery voltage on the following points: S12, S12C, the center legs of Q9 and Q12, the left (non-banded) end of D3, the left leg of U5, and the left (banded) end of D9.

You should have 5 volts at the following points: S5, the two +5V holes in the proto area, the right (non-banded) end of D9, the right leg of U5, the left (banded) end of D19, and pins 1, 20, and 31 of the CPU.

Let me know where you find the correct voltages, and where you find the wrong ones.

nebraska_e28 · Post by **nebraska_e28** » Thu Jun 17, 2010 9:07 pm

Just to clarify, are S12 & S12C the pins on the db37 and & S5 is the pin on db9?

Also, I didnt install Q9 & Q12 since they didnt seem to be needed. I'll be using fidle to control a separate board for the iacv.

Matt Cramer · Post by **Matt Cramer** » Fri Jun 18, 2010 4:16 am

nebraska_e28 wrote:Just to clarify, are S12 & S12C the pins on the db37 and & S5 is the pin on db9?

These are points on the board. They're not on any D-Subs.

Also, I didnt install Q9 & Q12 since they didnt seem to be needed. I'll be using fidle to control a separate board for the iacv.

You should still find the volts at the holes where Q12 and Q9 would have been.

nebraska_e28 · Post by **nebraska_e28** » Fri Jun 18, 2010 3:16 pm

Ok, found them. It was late & must've been tired.

Here are the voltages & additional info. Something must be way off. Keeping in mind that I did pass the test at step 55 & that did work. referenced here: viewtopic.php?f=30&t=38107

Pins jumpered on stim:
left 2 pins of the Primary Tach
WBO2

All stim dip switches are off.

Power supply voltage = 14.7
S12, S12C, = .90
the center legs of Q9 and Q12, = .58
the left (non-banded) end of D3, the left leg of U5, and the left (banded) end of D9. = .01
the left leg of U5, and the left (banded) end of D9 = .01

S5, & the two +5V holes in the proto area, = .01
S5, & the right (non-banded) end of D9, = .01
S5, & the right leg of U5, = .01
S5, & the left (banded) end of D19, = .01
S5, & pins 1, 20, and 31 of the CPU. = = .01

pic of board here:
http://e28-535i.com/upload/MSboard.jpg

nebraska_e28 · Post by **nebraska_e28** » Fri Jun 18, 2010 10:33 pm

Just did some more testing & adding this if its of any significance.

Across the middle leg & the leg closest the heat sink of Q19 & Q20 I get continuity. The same thing happens across Q15 & Q14 between the middle leg and the leg closest to DB37. Though I used very little heat, could I have shorted these out when soldering?

nebraska_e28 · Post by **nebraska_e28** » Sat Jun 19, 2010 9:28 pm

6/20 0024hrs update

I pulled Q19 & it tested fine with no short condition. While it was removed I tested the solder points that it mounts to & the same condition exists as noted above. I think it's safe to say that there must be a short somewhere on the circuit that includes Q19. Please advise.

Thanks again! While awaiting a response, I'll take a peak at the schematic to see if I get further.

Matt Cramer · Post by **Matt Cramer** » Mon Jun 21, 2010 4:34 am

Several of the transistors you mentioned have a 1 ohm, or even a 0.05 ohm, resistor across two of their legs. These probably aren't shorted out. It sounds as if the problem is on the 12 volt plane somewhere after the D10 diode. Is U5 getting hot?

nebraska_e28 · Post by **nebraska_e28** » Mon Jun 21, 2010 1:58 pm

Just checked & U5 doesn't get hot. Left it on for about 30 seconds. I also checked D10 & D9. They both still work oneway.

I did just realize, when I scrubbed the bottom of the board with alcohol it was 70% & not 90% as recommended.

Matt Cramer · Post by **Matt Cramer** » Tue Jun 22, 2010 3:36 am

Try desoldering the D10 diode and repeat the voltage check - what results do you get?

nebraska_e28 · Post by **nebraska_e28** » Tue Jun 22, 2010 10:10 am

Removed D10 & all tests done with cpu in board except for the last one.

Between S12, S12C, = jumps to 4.47v & then slowly decreases
the center legs of Q9 and Q12, = 0
the left (non-banded) end of D3, the left leg of U5, = .25 with stim voltage off & when 4.7 when powered up
the left leg of U5, and the left (banded) end of D9 = .34 with stim voltage off & same when powered on

S5, & the two +5V holes in the proto area, = 0
S5, & the right (non-banded) end of D9, = 0
S5, & the right leg of U5, = 0
S5, & the left (banded) end of D19, = 0
S5, & pins 1, 20, and 31 of the CPU. = 0

Matt Cramer · Post by **Matt Cramer** » Wed Jun 23, 2010 5:16 am

Check the mica insulators under Q9 and Q12; it sounds like they may be shorted to ground. Also make sure the trace that supplies them power isn't burned (it's on the bottom layer and readily visible).

nebraska_e28 · Post by **nebraska_e28** » Wed Jun 23, 2010 5:54 am

Removed the metal screws from both Q9/Q12 & lifted both of them slightly so they weren't in contact with the metal cooling strip. Applied power to the board, & am still seeing the light on the stim go dim after maybe 1/2 second. The trace on bottom wasn't burned either. I checked for continuity between the middle leg & DB37, we're good there. Man, I'm starting to feel like the little slow kid in math class.

All your help is appreciated Matt! What's next?

There's gotta be something simple I'm missing.

nebraska_e28 · Post by **nebraska_e28** » Thu Jun 24, 2010 6:13 am

Been searching the board for anything else out there that might point me in the right direction, but haven't found anything.

nebraska_e28 · Post by **nebraska_e28** » Fri Jun 25, 2010 5:31 am

6/25 update

With a little advice from Peter Florance, I was able to determine that D19 was bad. I hadn't noticed this before, but it was getting extremely hot even though installed correctly. I'll be buzzing DIY an email with this info.

LJ

nebraska_e28 · Post by **nebraska_e28** » Sun Jun 27, 2010 7:29 pm

The problem was C14 installed backwards! A little deductive reasoning, alot of patience, & attention to detail is what it took. I worked backwards though the instructions from the end back to the point where it was testing ok verifying EVERYTHING. Found the + symbol on C14 on the wrong side. Lesson well learned, lesson well taught.

All lights are working well now. I have yet to hook it back up to the computer, but am very optimistic about that.

Thanks for all your help Matt & Jerry!

Hopefully once I'm knowledgeable enough I can give back & help out the new guys troubleshooting their MS builds!

LJ

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Testing MS & all lights go dim / out

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