MS3X help. No 12V at U5
 

I'm at the step of checking voltages of my MS3 build. I have 12V into Pin 28 and GND to Pin 1.

I do not have 12V at pin 40 of U1 and I do not have 5V at the proper places at U1.

When I traced the 12V line I was able to follow it and I do have 12V at IAC1B, JS1 and pin 37 of U1.

I do not have 12V at U5. I've checked the diodes and they all look to be in the proper orientation. I do not have 12V at any of diodes D10-D13 which has me confused....


Any ideas of whats going on or what to try next?


https://www.miataturbo.net/attachmen...ine=1466129761

https://www.miataturbo.net/attachmen...ine=1466129761

https://www.miataturbo.net/attachmen...ine=1466129761

https://www.miataturbo.net/attachmen...ine=1466129761

https://www.miataturbo.net/attachmen...ine=1466129761

I meant to put this in the Megasquirt Sub-thread. If a mod could please move it I'd appreciate it. :likecat:

what writeup are you using to build your MS? You've added a ton of parts you don't need and didn't mod it for miata inputs yet.


if you dont have 12v at U5, then the problem is a trace on the PCB, 12 goes directly into PIN 1 of U5 from the DB37 connector. Look at the bottom of the board and look at the thick trace for it -- it also hits the middle pin of both the Q9 and Q12 FETs you didnt need to install.

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've been using the official MS3X v3.0 manual. Could you please link the recommended miata specific write up to follow. This is going on a 99 miata. Alot of threads end in you did it wrong because you didn't follow the official megasquirt manual so that's what I've been trying to use.

I tried following the trace as far as I could but there's to many components on the board. I'll remove those two FETs off the board tonight..

Thanks Matt, I will check this tonight when I'm home and report back.

looking again, it's a bit outdated and needs updates on the flyback and Alternator.

i dont like the way he does the harness.

http://westfieldmx5.sgrkempen.be/ms3/99-05-ms3/

Thanks for the link.
Should I remove the components that are not shown on this diagram?

https://www.miataturbo.net/attachmen...ine=1466183431

WOW, I made a dumb mistake. I thought I triple checked but I had 12V going into pin27 instead of pin 28 #facpalm

All voltages check out now. Thank you Matt!

Do you recommend removing the not needed components for the miata? or just leave them on the board?

Do you recommend removing the not needed components for the miata? or just leave them on the board?

no leave them. no point on removing.

id just remove r13 and install a 1k between the left pin of r13 and right of r45 just below it. that will provide the 1K pull up for the crank input.

do the jumpers in that writeup.

then do the expander board flyback mod. s19 to d1 on the expander.

and then set the pots, and youre pretty much ready to rock and roll.

I seem to have exceeded the max turns of the r56 pot. does any one know the equivalent resistance of that pot at Frank's recomended setting of

I've never checked voltages. never really had an issue (only on early units where we weren't adjusting enough).

Problem is I must have broke the pot adjustment mechanism so I have no way to know what 10.5 turns clockwise is. I already pulled the pot off the board and was hoping that if someone had a MS3 board accessible on their bench if they could measure the resistance across pins 1 and 3 so I can just pop an equivalent resistor in it's place. If not I can just source a replacement part from digikey but the resistor way would be cheaper and faster.

how does one do this? :P

JK I just ordered some more pot instead.

What needs updating on the flybacks?

Just need one wire from s19 to expander. See install docs.

Sorry, where can I find S19? I found S12 from Frank's write up but I don't see S19. And D1 is the same D1 as this pic right?

https://www.miataturbo.net/attachmen...ine=1467419995

He means S12. Looks like you found the right page in the manual

https://www.miataturbo.net/attachmen...ine=1467423201

I'm finishing up the wiring harness and had a couple of questions.

for SPR input on the MS3 board I have
SPR1 = CANH
SPR2 = CANL
SPR3 = KNK (from knock module)
SPR4 = empty

On Frank's wiring diagram it has SPR4 going to the Alternator. I think he uses his stand alone alternator board. If I'm using the MS3X for alternator control what jumper should I have connected to SPR4?

Also this is probably a dumb question but... OEM narrowband goes into MS23. I should wire my Wideband analog signal to EGO2 on MS3X22 right and just select that channel in the config? I can just leave my narrowband sensor plugged in and ignore the signal.

https://www.miataturbo.net/ecus-tuni...o-79347/page2/

From this thread it looks like I should have the Alternator pin (1O) go to Nitrous control 1 (24) and configure that as a PWM output.
And It looks like Alternator sense (1T) does not need to be connected?