Bad MS3x Board Voltage

[KYWalker]

Driving down the road, had a voltage spike (due to battery cable jumping off...stupid). No MS after that.

Summary of my testing so far:

From Matt Cramer:
"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."


In Diode Test mode on multi-meter, D19/D9/D17 show .165 in both directions...d12 shows 0 in both directions.

Removed one leg of D19:
12v at s12
1mv at S12c
12v at center legs of Q9/Q12
12v at Left end of D3
1.3mv at left left of U5
1.3mv at left 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."

I get .66v everywhere above.


I reinstalled D19 (D10 is removed) and have 12v at S12, center Q9/Q12, left D3.

I have 1.3mv at S12C, left U5, and left D9.

Notice that D10 is removed...otherwise, I get the short and no voltage anywhere.

Removed D11 & D12, now get:
.8V at S12C, left U5, and left D9.

Also found more bared traces...although they seem to be intact....between left D10 and left d12.

Greatly appreciate any help!

[billr]

Post pictures of both sides of the PCB, focusing on the area with bared traces.

[KYWalker]

Pics of bare traces

[billr]

I'm not seeing them, which side of the PCB (solder-side or component-side)? Which components do they connect?

[KYWalker]

Yeah, those were horrid, these are better.
Between IAC1A and IAC1A and between D10 and D12.

Sent from my XT1575 using Tapatalk

[billr]

Those don't look too worrisome to me. I'm going to wait a while and see If Jean advises on how to trouble-shoot, otherwise I will study the schematic and board layout to do so myself.

[KYWalker]

Update: I reinstalled D10 and D11.

I get 11.5v at S12, center Q9/Q12.
I get 10.75v at left U5, S12C, left D9.

I get 5v at S5, right U5, 5v Proto.

With D12 installed, I get a full on short....JimStim power led goes out.

[billr]

OK. Post again once D12 has been replaced.

[KYWalker]

It'll be a few days, unfortunately. I don't have those parts. I ordered extras though just in case... Thx

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[KYWalker]

D12 and D13 replaced and board shows good voltage now.... Until I plug in the MS3 processor board. Crud.

[KYWalker]

Pin 19 and Pin 20 on the MS3 processor card appear to be shorted (have continuity)...that seems wrong. Nothing looks visually bad/wrong/burnt.

I removed the MS3 card, hooked ground to pin 2, and then jumped pin 20 to the pin 20 socket....JimStim power led starts blinking....remove the jumper to pin 20, power led steady. Did the same test but used pin 19 for ground, with same results.

Sounds like I need a new MS3 card to me. Anyone else have other ideas/workarounds/fixes? It looks like pin 20 goes to Pin 26 of the DB37 and is used for TPS and Crank Signal...so I can't just 'do without it'.

I really wish I would quit breaking stuff....

[DaveEFI]

Pins 19 and 20 (on the daughter PCB) are supply and ground. Have you measured the resistance between them? Continuity devices can vary a bit.

If there is a fault on the daughter card, it can usually be repaired for a lot less cost than a new board.

[KYWalker]

1.2 Ohms

[DaveEFI]

1.2 Ohms

I'd guess you have a fault. Best to find out who can repair your board in your country.