board voltage wrong

[cukali]

Had made a MS3 with MS3x last fall. Installed almost all the options...knock, blue tooth, clock. Everything worked fine. Used the stim board and all systems proved good.


I finally got around to making a harness for an engine I had on a stand and when I hooked up the MS3 to the harness I noticed a draw on the battery supply. Could here it on the charger. So, I immediately disconnect and plugged it into the stim board....all worked fine. Grabbed an extra harness I had and hooked only the pos and neg to the charger...same thing. Tried the stim card again and worked fine. check blue tooth and all was good. Loaded a tune and was good. Got another V3 board and hooked it to the harness. Worked fine. (have 3 ms3s here). Anyway, when I hook it to a charger or 12v car battery it flashes all three light and they blink constant. when to the stim board with 12v adapter it works fine. Well I hooked it back to the engine harness and tried to connect with my blue tooth....nothing. opened the case and no burning smell, no visual burns, all looked good. Went back to hook to stim and nothing. Took the MS3 daughter board and hooked it to another board and it worked fine.

Now I checked voltage and on U5 right pin I get 11 volts to ground. I get 11 volts to ground on 40 pin socket also so I know something with the board is bad..... When I compaired ohms from a good board to this one between the u5 right pin to heat sink I get 700 ohms. On the new board I get only 0.7 ohms. I removed ALL power supply components and still read the same. Changed out the regulator and still the same. I have inspected all solderings and cannot find anything shorting. Changed out all the caps near U5 and still nothing. Wont work with stim or anything.....when all curcuits are hooked up I get 11 volts where I am suppose to get 5v.


Anything else I can check?

thnx.

[elaw]

Sounds like possibly a ground connection problem?

Using an ohmmeter, check resistance between pin 2 on U5 to the ground pins (1, 2, 7-19) on the main (not MS3X) board DB37. Resistance should be very low - under 1 ohm. If it's higher, there's a problem on the board.

If that test passes, plug the harness in and measure between pin 2 on U5 and where the MS is grounded (hopefully the engine block or head). Again resistance should be very low - under 1.0 ohm. If higher, there's a problem in the harness grounds.

[cukali]

Its someplace on the power circuit.

I am getting 10v on the right pin not 5v. It also has very little resistance between the right pin and ground (about 1 0hm.)


I just cannot find the short. I removed every component in the power circuit and ts still there.


Now I moved to another board and hit another wall. Un-believable. Cannot get the VR circuit to work...wont go above 1000 rpms. POTs adjusted every wich way and no joy. So I decide to use the opto circuit and set the stim to LS1 and LS1 in software and I get an error about fuel switching. Change the settings to 12-1 and error goes away but I cannot test my tune with that setting. Sounds like a glitch.

[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.

[elaw]

Also when you do tests, tell us where you've connected the negative (-) lead of the meter... that can have an impact on measurements.

[cukali]

Ok, got the voltages. Just to explain the events, the ECU worked fine on stim. All systems were good. Hooked to the engine using a battery charger and measuring amps....it drew 2 amps when I turned it on (nothing hooked up to injectors, coils, CAS, ect...) unplugged right away. hooked to stim, worked fine. Using a different MS3 harness I hooked only 12v and ground up and still drew 2 amps. Hooked back to stim, all worked fine. Connected to phones BT and worked. Connected back to charger and tried to connect to phone....wouldnt connect. Tried stim....worked. Tried charger again and didnt work. Went back to stim and tried and it DIDNT work. Opened up and inspected...looked fine. Measured voltages at U5 right side and got 10v same as middle. Measured resistance from right of u5 to ground and got 1 ohm!!.

Now after removing ALL power components and re-assemling its reads different voltages than last night but still way off from whats required....

S12C - 8.8v
Pin 20 - 0.58V
Pin 1 - 0.58v
Pin 31 - 0.58v
Right U5 - 1.58v
5v - 0.58v
Q9 center - 9.6v
Q12 center - 9.6v
Left U5 - 8.8v
S5 - 5.8v
D9 left - 8.8v
D19 left - 0.58v
D9 right - 0.58v

Definately a pattern. This time the U5 got hot and I had to use the battery charger not the stim. too much drain on stim it shuts off. THE DAUGHTER BOARD NOT CONNECTED and works fine in another board. I removed it when I first connected to engine.

Thing I checked....all components are lifted off the heat sink, checked both sides for solder bridges for about 2 hours with flashlight and mag glass, removed all power circuit components ans still found a short between U5 right side and ground, all diodes are correct, caps 16-17-23-F1 and others in powers supply circuit I replaced.



thanks for help all.

[cukali]

Removed the U5 chip and the stim doesnt overload. I measure ohms between pin 20 and ground and it shows 1 ohm, from right pin of U5 I get the same thing. There appears to be a short from the 5v circuit to ground someplace.

[DaveEFI]

Removed the U5 chip and the stim doesnt overload. I measure ohms between pin 20 and ground and it shows 1 ohm, from right pin of U5 I get the same thing. There appears to be a short from the 5v circuit to ground someplace.

Have you removed F1? If so, check both sides of that to ground on the board.

[cukali]

Yes I removed F1 and it still had the short....but I didnt measure from its pins.....will try it.


Ordered another board and components to get this job completed. Still need this board fixed though.

It acts like a solder bridge but d*** if I can find it. Using a magnifying glass and flashlight I searched every solder joint and nothing.

Could it be in the board itself? Seams like it was fine on stim but with a powerful power supply it might have made the short worse.

[kjones6039]

Seams like it was fine on stim but with a powerful power supply it might have made the short worse.

Almost 60 years of electronics tells me-- if it's shorted, it's shorted, irrespective of the power supply!

Just my amateur opinion of course..........

Ken

[cukali]

Yes, what I mean is that a short with resistance can become a short without if amps cause an arc to "weld" it.

[DaveEFI]

Yes I removed F1 and it still had the short....but I didnt measure from its pins.....will try it.


Ordered another board and components to get this job completed. Still need this board fixed though.

It acts like a solder bridge but d*** if I can find it. Using a magnifying glass and flashlight I searched every solder joint and nothing.

Could it be in the board itself? Seams like it was fine on stim but with a powerful power supply it might have made the short worse.

Measuring either side of F1 to ground will (should ) tell you which side of it the short is. And since it's still there must be the input side. Do the same with either side of U5 since you've removed it. My guess is one of the tantalum caps has failed short circuit and damaged the PCB - did you have a fuse in the supply, and what value? Most likely is C16 as that is before the 5 volt reg. A short after the reg should have caused it to shut down - rather than damage the PCB. However, if a track has burnt out it should be visible.

Sadly all this is just guessing based on faults I've seen. I don't claim to have seen every one.

[kjones6039]

Yes, what I mean is that a short with resistance can become a short without if amps cause an arc to "weld" it.

By definition, an "arc" implies a gap which also implies an open circuit as opposed to a short circuit.

Ken

[cukali]

Yes I removed F1 and it still had the short....but I didnt measure from its pins.....will try it.


Ordered another board and components to get this job completed. Still need this board fixed though.

It acts like a solder bridge but d*** if I can find it. Using a magnifying glass and flashlight I searched every solder joint and nothing.

Could it be in the board itself? Seams like it was fine on stim but with a powerful power supply it might have made the short worse.

Measuring either side of F1 to ground will (should ) tell you which side of it the short is. And since it's still there must be the input side. Do the same with either side of U5 since you've removed it. My guess is one of the tantalum caps has failed short circuit and damaged the PCB - did you have a fuse in the supply, and what value? Most likely is C16 as that is before the 5 volt reg. A short after the reg should have caused it to shut down - rather than damage the PCB. However, if a track has burnt out it should be visible.

Sadly all this is just guessing based on faults I've seen. I don't claim to have seen every one.

Its only right pin of U5.

I replaced all the power supply components. I am guessing your right about the board. I am going to dis-assemble the board completely in hopes its a hidden solder bridge.

[cukali]

Yes, what I mean is that a short with resistance can become a short without if amps cause an arc to "weld" it.

By definition, an "arc" implies a gap which also implies an open circuit as opposed to a short circuit.

Ken

Anything at all helpful you can add or is it just the troll in you?

http://en.wikipedia.org/wiki/Short_circuit

Fifth paragraph down in examples...... I am having enough problems solving my issues...I cant solve yours.

Thanks for your help.

[kjones6039]

or is it just the troll in you?

I'm not sure what that means.... Perhaps you can send me another wiki link?

I think you missed my point. IMHO, a short is a short, an open is an open, and ne'er the twain shall meet. I should have made it clear that I was passing along an opinion and offer my most humble apologies! I shall refrain from further comment.

Ken

[DaveEFI]

Its only right pin of U5.

I replaced all the power supply components. I am guessing your right about the board. I am going to dis-assemble the board completely in hopes its a hidden solder bridge.

I'd caution against removing comps on spec.

If by the right pin on U5, you mean Pin 1 the 12v input to it, there are very few components between that and ground which could cause the short. But you've said you've removed these? If so, and the short is still there, try removing D3 and report the result. And if there's anything connected to S12 or S12c, disconnect those. But do things one at a time and measure.

[aidandj]

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.

I am running into the same problem. And when I test voltages everything is good except for the left end of D19 only has .25 volts instead of 5 volts. Any ideas?

[Matt Cramer]

I am running into the same problem. And when I test voltages everything is good except for the left end of D19 only has .25 volts instead of 5 volts. Any ideas?

If it's the same problem as the original poster, replacing the same component he changed would fix it.

If it's a similar problem, check if D19 is getting hot when powered up, and if so, replace it.

[billr]

I'm late to this party, but want to add that I would avoid using a battery-charger for a power supply unless there was also a battery connected. Automotive battery-chargers often have a lot of AC ripple and the peak voltages may well exceed what some of the MS components can easily handle. Also, Ken, I have run into a phenolic fuse-holder that got a "carbon track" on it. It read fine with a (20M max) ohmmeter, but when 480VAC was applied it would turn into a hard short. Not the same as what we are talking about here, of course, but FYI.