Stim or MS 2.2 voltage problem

magflip · Post by **magflip** » Mon Oct 20, 2014 1:21 pm

Hi guys!
Sometime ago I bought a unassembled kit of v2.2. I assembled it but never tested, because I have stopped my project.
Now, I resumed the project and started to test the MS. I built the stim like the attachment and plugged on MS.
Unfortunately, the stim (or MS, or both) seems not work. The leds IDL and FP1 light, but INJ1 and INJ2 not light (even flashes).
I tested pins of dip-40 like the maual says (combination of pins 1, 20, 31 with 2, 19 and 31) and all tests marks 0.66~0.68v.
I already replaced the 555 of stim, checked solder of db37 and the another components. Every seems ok.
I don't know what I do now...
Pics of MS1v2.2 and stim here => https://www.dropbox.com/sh/543nc03zt49c ... SD4Qa?dl=0.
Somebody can help me?

Matt Cramer · Post by **Matt Cramer** » Tue Oct 21, 2014 5:52 am

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: the small hole to the right of the larger three holes marked X11, X12, and X13, the top (non-banded) end of D20, the left leg of U5, and the left (banded) end of D12.

You should have 5 volts at the following points: the right (non-banded) end of D12, the right leg of U5, 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

trakkies · Post by **trakkies** » Tue Oct 21, 2014 8:30 am

The injector lights won't flash until you have a tach signal seen by MS. Does Tuner Studio show that tach signal? Have you loaded in the code or checked if has been done?

magflip · Post by **magflip** » Tue Oct 21, 2014 3:19 pm

Matt Cramer wrote: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: the small hole to the right of the larger three holes marked X11, X12, and X13, the top (non-banded) end of D20, the left leg of U5, and the left (banded) end of D12.

You should have 5 volts at the following points: the right (non-banded) end of D12, the right leg of U5, 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

Matt, here's the results:

the small hole to the right of the larger three holes marked X11, X12, and X13 = 9.38v
the top (non-banded) end of D20 = 9.38v
the left leg of U5 = 0.15v
the left (banded) end of D12 = 0.16v

the right (non-banded) end of D12 = 0.67v
the right leg of U5 = 0.67v
and pins 1, 20, and 31 of the CPU = 0.67v

The problem is on U5?

magflip · Post by **magflip** » Tue Oct 21, 2014 3:28 pm

trakkies wrote:The injector lights won't flash until you have a tach signal seen by MS. Does Tuner Studio show that tach signal? Have you loaded in the code or checked if has been done?

trakkies, TunerStudio even connect to the MS. I don't loaded the tach signal in the code and I don't know how check it. How can I do?

trakkies · Post by **trakkies** » Wed Oct 22, 2014 12:29 am

The Stim generates the tach signal (rpm). However, it looks like the lack of 5 volts is the first thing to sort.

First check D13 is fitted the correct way round. And the voltage to ground either side of it. It should be approx battery volts on both sides. If it is, next check continuity between the banded end on D13 to pin 1 of U5.

magflip · Post by **magflip** » Wed Oct 22, 2014 12:49 pm

trakkies wrote:The Stim generates the tach signal (rpm). However, it looks like the lack of 5 volts is the first thing to sort.

First check D13 is fitted the correct way round. And the voltage to ground either side of it. It should be approx battery volts on both sides. If it is, next check continuity between the banded end on D13 to pin 1 of U5.

Results of D13:
non-banded side to pin 19 of dip40 = 9v
banded side to pin 19 of dip40 = 0.16v
banded side and left leg of U5 = 0v
banded side and right leg of U5 = 0.46v

trakkies · Post by **trakkies** » Thu Oct 23, 2014 12:23 am

Are you using a PP3 battery as the power supply? If so, and there's 9v on one side of D13 but not the other, D13 must have failed open circuit.
Have you got a DVM with a diode test function? Will normally be marked with the diode symbol. If so, you can test the diode in circuit. Black lead to band end.
DVM should lead 0.5-0.6v or OK. Reverse the leads. Should read approx 3v or perhaps overload depending on make of DVM

If you're using higher current supply than a PP3, and there's a short on the output side of D13, it would get hot.

It is the same sort of diode as D12 and D14?

magflip · Post by **magflip** » Thu Oct 23, 2014 3:16 am

trakkies wrote:Are you using a PP3 battery as the power supply? If so, and there's 9v on one side of D13 but not the other, D13 must have failed open circuit.
Have you got a DVM with a diode test function? Will normally be marked with the diode symbol. If so, you can test the diode in circuit. Black lead to band end.
DVM should lead 0.5-0.6v or OK. Reverse the leads. Should read approx 3v or perhaps overload depending on make of DVM

If you're using higher current supply than a PP3, and there's a short on the output side of D13, it would get hot.

It is the same sort of diode as D12 and D14?

trakkies, I use a "cellphone charger" as power supply. I measure it before plug in stim and provides approx 12.3v.
My DVM has diode test but I haven't tested diodes before solder. Can I test now with diodes soldered on MS? To test this diode, the power supply has be connected?
The diodes D12 and D14 seems the same.

D12_D14.jpg

trakkies · Post by **trakkies** » Thu Oct 23, 2014 7:03 am

You can often test a diode in place. Don't power up the MS while doing so - the DVM supplies the volts to test the diode. D14 is the same and should give the same results with your DVM.

FWIW, it's best to use a decent power supply designed for the job. I've had problems loading code with one which sort of worked otherwise. Something like a 1 amp 13.8v one would be ideal.

magflip · Post by **magflip** » Thu Oct 23, 2014 11:48 am

trakkies wrote:You can often test a diode in place. Don't power up the MS while doing so - the DVM supplies the volts to test the diode. D14 is the same and should give the same results with your DVM.

FWIW, it's best to use a decent power supply designed for the job. I've had problems loading code with one which sort of worked otherwise. Something like a 1 amp 13.8v one would be ideal.

I measured the D12, D13 and D14 diodes. All results are 630 on DVM (black lead on banded side). Reversed leads showed none in DVM.
What I've to check now?

trakkies · Post by **trakkies** » Fri Oct 24, 2014 12:30 am

Right. I'm just not sure how you can have 9v on one side of D13 but near zero on the other without it blowing or getting hot.
However, it looks like you have a short on the 5v rail. There should be 12v on pin1 of U5 and 5v on pin 3.
Have you checked these with the processor removed?

Is C16 a tantalum cap? Sort of beige blob? If so, they can fail short circuit.

Sadly, there are several reasons why there could be a short on the 5 volt rail.

magflip · Post by **magflip** » Fri Oct 24, 2014 1:50 am

trakkies wrote:right. I'm just not sure how you can have 9v on one side of D13 but near zero on the other without it blowing or getting hot.
However, it looks like you have a short on the 5v rail. There should be 12v on pin1 of U5 and 5v on pin 3.
Have you checked these with the processor removed?

Is C16 a tantalum cap? Sort of beige blob? If so, they can fail short circuit.

Sadly, there are several reasons why there could be a short on the 5 volt rail.

I tested U5 too and there no 12v and 5v. All tests I've done was without processor.
C16 is beige, like shown in attachment.
What you propose to I do now?

trakkies · Post by **trakkies** » Fri Oct 24, 2014 5:17 am

What do you get if the measure the resistance of C15 with MS not powered up? Then swap the DVM leads round and measure again?

I'm wary about saying to remove any components as it's possible to damage the PCB.

magflip · Post by **magflip** » Sat Oct 25, 2014 4:31 am

trakkies wrote:What do you get if the measure the resistance of C15 with MS not powered up? Then swap the DVM leads round and measure again?

I'm wary about saying to remove any components as it's possible to damage the PCB.

I'm travelling today. Tomorrow night I'll post results of C15.
When I powered stim with 12v first time, I inverted polarity and Q3 was fried but I already replaced it.
What kind of damage can be done in PCB by replacing components?

trakkies · Post by **trakkies** » Sat Oct 25, 2014 6:04 am

It's the removal which can do the damage. I've seen tracks pulled off the board by this being done carelessly.

The snag with giving advice on here is not knowing the skills of everyone.

FWIW, I've repaired several MS (although V3 boards) where this cap has shorted. So it would be the first thing I'd look at. But of course that's no guarantee it's the fault here.

magflip · Post by **magflip** » Sat Oct 25, 2014 6:18 am

I really appreciate your help. Backing home I'll replace C15 immediately.
Originally manual indicates tantalum capacitors for C15 and C16. This is really necessary? My knowledge of eletronics is basic...

trakkies · Post by **trakkies** » Sat Oct 25, 2014 7:53 am

When you remove it, do check it for a short circuit. And check for a short between Pin3 of U5 and ground before replacing. With fault finding it's often just a case of elimination. Tantalum have a very good performance and are small in size. But ordinary aluminium electrolytic have improved too. I'd say it's not a demanding application so a good quality low ESR electrolytic would be ok here.

magflip · Post by **magflip** » Mon Oct 27, 2014 3:42 am

I measured the C15 and C16 capacitors. C15 seems ok but C16 looks shorted, apparently isn't charging.
Anyway, I'll replace both and then I'll test MS+stim again.

magflip · Post by **magflip** » Mon Oct 27, 2014 4:56 pm

So, I've tested C15, C16 and U5 after replacing these components and are the same results.
- I measured resistance of C15, (normal leads and reversed leads) and DVM flashed a number then showed "1." (20k scale of DVM)
- I measured resistance of C16, (normal leads and reversed leads) and DVM showed "0.95" (20k scale of DVM);
- I measured pin3 of U5 and ground and DVM showed 0.65v;
- I measured pin1 of U5 and ground and DVM showed 0.40v;

All tests I've done was without processor.

Apparently problem wasn't in C15, C16 or U5. I don't know what I do now. I'm almost giving up.
Any suggestions to me?

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