High voltage on NB1 alt output, new megasquirt install
 

Car in question is a 99 manual with 93,000mi on the clock. Bone stock except for some wheels and an unidentified header.

From the forum I bought a used DIYPNP Ms2 for NB1 miatas with the voltage regulator circuit installed (according to the seller) and finally installed it in car yesterday.
I installed latest firmware (MsExtra 3.4.2) before putting the ECU in the car.
Downloaded a basemap from DIYAutotune.

Got the car idling and warming up but with some hiccups and bumps. Also noticed a pronounced clicking sound coming from behind the passenger compartment; fuel pump?
I took a log this morning on startup and noticed that my battery voltage was showing almost 18v! Jumped out and checked at alternator with a multi-meter, and it was putting out the same.
I immediately shut the car off for fear or frying my dear-to-me Megasquirt.

I have checked resistance from the battery neg terminal to fender ground and it is very low.

I'm not sure how to identify if I actually have the correct circuit installed on my megasquirt or if there is a setting in Tunerstudio that controls voltage output that I am missing. I am very much a noob with megasquirt.

Thoughts?

open the case and see of the circuit is in there

Prior to putting the unit in the car, I had cracked it open and seen what looked like the circuit attached to the board.

Got in contact with the seller who says that there is a small adjustable dial on the circuit itself that can be turned to dial in the regulation. Not sure if it responsible for the 18v output, but will try to open it tomorrow and see.

Westfieldmx5, I guess you'd recognize this:

https://cimg8.ibsrv.net/gimg/www.mia...5df734a11f.jpg

So I dialed the potentiometer fully counter-clockwise until it made a slight clicking noise (25 turns max if my interwebs searching was correct).
Started the car and still got 18v in tuner studio. Scrambled to the front of the car and verified the same voltage coming from the alternator before I shut everything down.
Am I doing something incorrectly? Anybody have any ideas as to what's going on?

Get yourself a cheap LED panel volt meter and you will know the alt status without logging or laptop. Best $5 I've invested.

I've burned an ABS unit with too high voltage and countless MTX-L's.

Also, be prepared to capitulate to an internally regulated alt.

one of those transistors looked installed backwards...

PN2907A?
I'm ignorant enough of small electronic components to have never noticed that myself. Thank you very much for casting your gaze upon it.
I guess the next step is to try switching it around myself. Any chance the incorrect orientation has somehow fried or otherwise damaged the transistor?

Both PN's are reversed, but it's probably correct. The PN2907A is a typical US component and not easy available in Europe. I now build the boards with the Euro equivalent (BC327). It's identical but with a reversed footprint.
Did the guy you bought it from assemble the alternator board himself or did he buy it assembled from me?
The blue pot is indeed to set the voltage. Turning left lowers voltage. If you've turned it to the left all the way, the voltage should be at its minimum, about 13V.

Look at how the board is assembled- no way that's your handiwork. Whoever did this needs to get slapped on the wrist with a hot radiator soldering iron.

LOL, so true :)

When I PMed and asked if the circuit actually ever worked for the previous owner, I got no reply. Then I managed to find posts from late last year where he could never get it working, and had apparently done the work himself :sad2:
It was sold as a Megasquirt with Voltage circuit installed, but I guess I should have asked some more questions.

Was able to remove the backwards transistor (before I saw your post Westfieldmx5), but also managed to turn it into 3 pieces in the process. Can you tell soldering is not my forte?

My plan was to order this transistor and see if it doesn't fix the problem, but you're saying that both PN's are backwards; is this assuming that it was your board with the euro-spec transistors? I'm thoroughly confused.
My son was just born Tues and is in NICU until next week, so this is obviously low priority at the moment, but if you guys come up with any additional info or suggestions, please throw them at me.

Yes I was assuming the board has the euro spec BC327 transistors. It doubt the previous owner would have installed both PN2907A transistors backwards by accident.
It shouldn't be confusing at all. The part number of the transistor is printed on it. It's very easy to see if you have PN2907's or BC327's. If your board has BC327's (as I suspect), they need to be installed backwards. If your board has PN2907's, they need to be installed the correct way round, like the silk screen suggests.
Your link is correct, as they are PN2907's make sure to install them the correct way round.

It's difficult to say what went wrong with the board, so you might want to replace the TL431 as well. They're very cheap and since you're ordering anyway ;).

it only looks like one is installed backwards, and Q1 is installed correctly.

doesnt make sense that a person would install two different PN transistors there...


https://cimg0.ibsrv.net/gimg/www.mia...feb35c7854.png

The pot looks like it could be upside down as well. If it is a common wiper configuration, that would reverse the direction of adjustment.

OMG, must learn to look closer :greddy2:. You're both correct. Only one transistor is backwards and the pot is upside down ....

i noticed the pot too, but pot upside down shouldn't matter, right?

It will most likely reverse the direction of the voltage control.https://cimg6.ibsrv.net/gimg/www.mia...f5d44780c5.jpg

Sheesh, what a cluster.
Transistors are ordered, and will be put on the board when they arrive, hopefully by mid-week. Then I'll baseline the pot in the fully clockwise direction and work my way back from there in adjustment.. Thanks again everyone for having a look, I'll let you know how things work out.

Mission Success!

I replaced the offending transistor (ordered a desoldering pump, what a difference!) and installed the new transistor in the correct orientation. While I was at it, I decided to actually mount the alternator circuit instead of leaving it flopping around.


https://cimg8.ibsrv.net/gimg/www.mia...2d9625843b.jpg

I also drilled a small hole through the cover of the MS through which I could adjust the alternator circuit, with a small rubber bung closing the hole when I'm not working on it. I HATE taking the MS in and out. I'm 6'1", and laying up-side-down under the dash or kneeling on gravel doesn't work for me anymore. I had originally mounted the MS with zip ties, but am in the process of changing over to velcro straps.

https://cimg4.ibsrv.net/gimg/www.mia...ff17285842.jpg


Started the car and after warm up I began adjusting the potentiometer until I reached 14v. Interestingly, turning clockwise still caused an increase in voltage even though the potentiometer seems to be installed backwards.
Now that the alternator is working correctly again, I can continue idle tuning and then get some road time. Thanks for your help guys.

Pot is probably not in a common wiper configuration. No big deal, glad to hear it is working!