MS2 V3.0 lost tacho signal. Help needed urgently

Ask questions about DIY board assembly issues, fault finding and testing. (Covers all Megasquirt versions and board.)

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brad91
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Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by brad91 »

heres a couple pics of the u7 chip from top and bottom. Havnt touched it in a few days as ive been struggling trying to get 2 cars ready for a track day! But after this weekend I want to get this car running so hopefully someone can give me a magical cure to fix this :(
IMG_0621.jpg
IMG_8905.jpg
brad91
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Posts: 29
Joined: Mon Jul 21, 2014 6:31 pm

Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by brad91 »

anyone?
brad91
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Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by brad91 »

Not sure if it would make any difference but the engine has low impedence injectors?
Matt Cramer
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Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by Matt Cramer »

Matt Cramer -1966 Dodge Dart slant six running on MS3X
brad91
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Joined: Mon Jul 21, 2014 6:31 pm

Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by brad91 »

Hadnt seen that page before!! thanks. Ive seen that schematic and followed it with my scope but hadnt seen the info thats on that page.
Will give that a quick try tonight. Ive already replaced U7.

Couple questions however:

So, to test this one, apply ground and 5V power to the input (pin 24 of the DB37 connector, VRIN for a V3.0 , or pin 1 of JP1 for a V3.57), and check the voltage at pin 2 of U7. You should see about 5V at this pin with 5V applied to the input, within about 0.5 volts. When you ground the input, pin 2 of the U7 should have from zero to 0.7 volts. If the voltage is significantly higher, Q22 is the most likely part to fail.

Do I need to hook 5v direct to the VRin or is hooking up my stim fine? When grounding the input, Do you jumper VRin to the earth on the stim? (guessing that would be the most accurate earth)


Once you have adjusted R56, apply 5 volts to the input.Assuming apply to VRin? or to the input of R56? You should see between 4.5 and 5 volts at pin 2 of U7, and between 3.5 and 5 volts at pin 1 of U7. The MC34072 should be closer to 5 volts; older kits that used the LM2904 may be closer to 3.5.

Next, ground the input pin.Once again assuming ground VRin? This should give you from 0 to 1 volts at pin 1 of the U7. If you see the correct input voltages on pins 2 and 3 of U7, but the output voltage does not change as it should, you need to replace U7.

Just thought I should check about the grounding and applying 5v to the correct components as im not sure if you would apply it straight to part way along a circuit to test an individual component.


Also, with the stim hooked up im going to get varying voltages (as the wave comes through) so should I be getting a 5v DC adaptor (or some resistors for my 12v) and hooking that straight to the correct pin so I have a steady voltage to test?
brad91
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Posts: 29
Joined: Mon Jul 21, 2014 6:31 pm

Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by brad91 »

ok so did some tests:

The circuit from VRIN to pin 2 of U7 is essentially a filter. It tracks the input voltage to the circuit, but absorbs noise. In steady state testing, it will produce a few changes to the signal, but what you see on the input (VRIN) will be very similar to what you see on the output (Pin 2 of U7).

So, to test this one, apply ground and 5V power to the input (pin 24 of the DB37 connector, VRIN for a V3.0, or pin 1 of JP1 for a V3.57), and check the voltage at pin 2 of U7. You should see about 5V at this pin with 5V applied to the input, within about 0.5 volts. When you ground the input, pin 2 of the U7 should have from zero to 0.7 volts. If the voltage is significantly higher, Q22 is the most likely part to fail.

VRIN = 4.3V
Pin 2 = 4.6V
Grounded input - pin 2 = .95V


The U7 chip compares the voltage at pin 2 to the voltage at pin 3. Adjust R56 to get between 1 and 2 volts at this pin. The output (pin 1) of U7 is high when you have more volts on pin 3 than pin 2, and low when you have more volts on pin 2 than pin 3.

Once you have adjusted R56, apply 5 volts to the input. You should see between 4.5 and 5 volts at pin 2 of U7, and between 3.5 and 5 volts at pin 1 of U7. The MC34072 should be closer to 5 volts; older kits that used the LM2904 may be closer to 3.5.

pin 2 = 4.6v
pin 3 = 1.75v
pin 1 = 62v!!!no idea how I get that??


Next, ground the input pin. This should give you from 0 to 1 volts at pin 1 of the U7. If you see the correct input voltages on pins 2 and 3 of U7, but the output voltage does not change as it should, you need to replace U7.

grounded pin 2 - .95v
grounded pin 3 - 2v
grounded pin 1 - 3.75v


so am i right in my assumption that it is possibly q22?
Matt Cramer
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Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by Matt Cramer »

The "input pin" is VRIN in all cases.

First we need to figure out what that "62V" measure is. Any chance it's an auto-ranging meter and that's 62 mV (0.062 V) instead?
Matt Cramer -1966 Dodge Dart slant six running on MS3X
brad91
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Posts: 29
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Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by brad91 »

ah yes it is auto ranging. I didnt look at that all I saw was the decimal point move way down haha. Will check that tonight! I dare say it will be 62mV as its a high end automotive meter and does AC/DC automatically so would assume it will def be auto ranging. Its the SP Tools Automotive multimeter.

I did this test with my stim hooked up and the RPM pot turned all the way down to give the highest voltage (closest to 5v) I could get. Will that be accurate enough or do I need to go buy a 5v power source and connect to VRin directly?

Also when I was grounding the input I had my meter with the earth wire of the stim connected to it and clipped that onto the jumper underneath VRin (something to clip to so I had free hands to do other things). This way I had an accurate earth
brad91
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Joined: Mon Jul 21, 2014 6:31 pm

Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by brad91 »

guys?
Matt Cramer
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Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by Matt Cramer »

It looks as if the circuit itself is working OK, then.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
brad91
MS/Extra Newbie
Posts: 29
Joined: Mon Jul 21, 2014 6:31 pm

Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by brad91 »

So looking like a need a new daughterboard?
Matt Cramer
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Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by Matt Cramer »

I would try reflashing firmware and starting with a fresh tune. The tune is easier to damage than the hardware.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
Rick Finsta
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Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by Rick Finsta »

The joints on U4 do not look like they were all completed in your picture (not saying the injector circuit is causing this problem, just that it indicates you might have other soldering issues throughout your board); I would go over your whole board and reflow every joint, adding solder where necessary, and clean up the overflow where necessary with desoldering braid. Then, clean the board with 90% IPA (rubbing alcohol) and a soft toothbrush, let it dry, and try again. I think you might have a lot of cold or intermittent joints there.

Reflowing and cleaning up my original solder work cleared up a few issues I was having early in my build process. In fact, after spending days trying to figure out why I couldn't get comms, it was because my RS232 chip wasn't fully soldered in! :oops:
brad91
MS/Extra Newbie
Posts: 29
Joined: Mon Jul 21, 2014 6:31 pm

Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by brad91 »

i replaced U4 myself. That was after the problem.

I have tried reloading firmware but it wont stay connected long enough to do so. It just drops out continually.

Whats the best way to reflow the joints? new to soldering boards. I have done a lot of soldering with wires and can get that all neat as hell but my setup appears to suck for the board haha.

What size solder do you guys use? Some super thin stuff or is thicker stuff ok? I bought some 1/1.2mm lead free solder. Should I be using a very sharp point on the iron? (will need to go buy one if thats the case)
Matt Cramer
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Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by Matt Cramer »

Lead free solder isn't nearly as easy to work with as the old fashioned leaded stuff, nor is it as reliable. There's a reason the automotive industry is exempt from RoHS. But the main thing with reflow is to heat it with the iron until both the leads and PCB tin are hot, and make sure there's enough solder on there that you don't have a dry joint.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
Rick Finsta
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Re: MS2 V3.0 lost tacho signal. Help needed urgently

Post by Rick Finsta »

My opinions:

Use flux core solder with lead. I use the thin stuff on the wall at RadioShack.
Use at least a 25W iron, keep the tip clean and tinned. One of the little tip cleaning/tinning canisters is helpful, as is the little stand with a sponge. Sharp point is easier to work with on the confines of these boards.
Use BRIGHT lighting. Use a magnifying glass if necessary to really see the board.

Just touch the tip of the iron to the pad on the board and the leg of the component at the same time, and when you see it flow then dab a bit more solder in there if you don't see a slight bump of solder on both sides of the board. Not a ton of solder, but I don't like to see them convex and I like to see it look even on both sides.
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